Shuffle persist event data store functions. (#7440)

The aim here is to get to a stage where we have a `PersistEventStore` that holds all the write methods used during event persistence, so that we can take that class out of the `DataStore` mixin and instansiate it separately. This will allow us to instansiate it on processes other than master, while also ensuring it is only available on processes that are configured to write to events stream.

This is a bit of an architectural change, where we end up with multiple classes per data store (rather than one per data store we have now). We end up having:

1. Storage classes that provide high level APIs that can talk to multiple data stores.
2. Data store modules that consist of classes that must point at the same database instance.
3. Classes in a data store that can be instantiated on processes depending on config.

19 files changed, 1376 insertions, 1235 deletions

diff --git a/changelog.d/7440.misc b/changelog.d/7440.misc
new file mode 100644
index 0000000000..2505cdc66f
--- /dev/null
+++ b/changelog.d/7440.misc
@@ -0,0 +1 @@
+Refactor event persistence database functions in preparation for allowing them to be run on non-master processes.
diff --git a/synapse/storage/data_stores/__init__.py b/synapse/storage/data_stores/__init__.py
index e1d03429ca..7c14ba91c2 100644
--- a/synapse/storage/data_stores/__init__.py
+++ b/synapse/storage/data_stores/__init__.py
@@ -15,6 +15,7 @@
 
 import logging
 
+from synapse.storage.data_stores.main.events import PersistEventsStore
 from synapse.storage.data_stores.state import StateGroupDataStore
 from synapse.storage.database import Database, make_conn
 from synapse.storage.engines import create_engine
@@ -39,6 +40,7 @@ class DataStores(object):
         self.databases = []
         self.main = None
         self.state = None
+        self.persist_events = None
 
         for database_config in hs.config.database.databases:
             db_name = database_config.name
@@ -64,6 +66,13 @@ class DataStores(object):
 
                     self.main = main_store_class(database, db_conn, hs)
 
+                    # If we're on a process that can persist events (currently
+                    # master), also instansiate a `PersistEventsStore`
+                    if hs.config.worker.worker_app is None:
+                        self.persist_events = PersistEventsStore(
+                            hs, database, self.main
+                        )
+
                 if "state" in database_config.data_stores:
                     logger.info("Starting 'state' data store")
 
diff --git a/synapse/storage/data_stores/main/__init__.py b/synapse/storage/data_stores/main/__init__.py
index cd2a1f0461..5df9dce79d 100644
--- a/synapse/storage/data_stores/main/__init__.py
+++ b/synapse/storage/data_stores/main/__init__.py
@@ -34,6 +34,7 @@ from synapse.util.caches.stream_change_cache import StreamChangeCache
 from .account_data import AccountDataStore
 from .appservice import ApplicationServiceStore, ApplicationServiceTransactionStore
 from .cache import CacheInvalidationWorkerStore
+from .censor_events import CensorEventsStore
 from .client_ips import ClientIpStore
 from .deviceinbox import DeviceInboxStore
 from .devices import DeviceStore
@@ -42,16 +43,17 @@ from .e2e_room_keys import EndToEndRoomKeyStore
 from .end_to_end_keys import EndToEndKeyStore
 from .event_federation import EventFederationStore
 from .event_push_actions import EventPushActionsStore
-from .events import EventsStore
 from .events_bg_updates import EventsBackgroundUpdatesStore
 from .filtering import FilteringStore
 from .group_server import GroupServerStore
 from .keys import KeyStore
 from .media_repository import MediaRepositoryStore
+from .metrics import ServerMetricsStore
 from .monthly_active_users import MonthlyActiveUsersStore
 from .openid import OpenIdStore
 from .presence import PresenceStore, UserPresenceState
 from .profile import ProfileStore
+from .purge_events import PurgeEventsStore
 from .push_rule import PushRuleStore
 from .pusher import PusherStore
 from .receipts import ReceiptsStore
@@ -88,7 +90,7 @@ class DataStore(
     StateStore,
     SignatureStore,
     ApplicationServiceStore,
-    EventsStore,
+    PurgeEventsStore,
     EventFederationStore,
     MediaRepositoryStore,
     RejectionsStore,
@@ -113,8 +115,10 @@ class DataStore(
     MonthlyActiveUsersStore,
     StatsStore,
     RelationsStore,
+    CensorEventsStore,
     UIAuthStore,
     CacheInvalidationWorkerStore,
+    ServerMetricsStore,
 ):
     def __init__(self, database: Database, db_conn, hs):
         self.hs = hs
diff --git a/synapse/storage/data_stores/main/censor_events.py b/synapse/storage/data_stores/main/censor_events.py
new file mode 100644
index 0000000000..49683b4d5a
--- /dev/null
+++ b/synapse/storage/data_stores/main/censor_events.py
@@ -0,0 +1,213 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+from typing import TYPE_CHECKING
+
+from twisted.internet import defer
+
+from synapse.events.utils import prune_event_dict
+from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.storage._base import SQLBaseStore
+from synapse.storage.data_stores.main.cache import CacheInvalidationWorkerStore
+from synapse.storage.data_stores.main.events import encode_json
+from synapse.storage.data_stores.main.events_worker import EventsWorkerStore
+from synapse.storage.database import Database
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+
+logger = logging.getLogger(__name__)
+
+
+class CensorEventsStore(CacheInvalidationWorkerStore, EventsWorkerStore, SQLBaseStore):
+    def __init__(self, database: Database, db_conn, hs: "HomeServer"):
+        super().__init__(database, db_conn, hs)
+
+        # This should only exist on master for now
+        assert (
+            hs.config.worker.worker_app is None
+        ), "Can only instantiate CensorEventsStore on master"
+
+        def _censor_redactions():
+            return run_as_background_process(
+                "_censor_redactions", self._censor_redactions
+            )
+
+        if self.hs.config.redaction_retention_period is not None:
+            hs.get_clock().looping_call(_censor_redactions, 5 * 60 * 1000)
+
+    async def _censor_redactions(self):
+        """Censors all redactions older than the configured period that haven't
+        been censored yet.
+
+        By censor we mean update the event_json table with the redacted event.
+        """
+
+        if self.hs.config.redaction_retention_period is None:
+            return
+
+        if not (
+            await self.db.updates.has_completed_background_update(
+                "redactions_have_censored_ts_idx"
+            )
+        ):
+            # We don't want to run this until the appropriate index has been
+            # created.
+            return
+
+        before_ts = self._clock.time_msec() - self.hs.config.redaction_retention_period
+
+        # We fetch all redactions that:
+        #   1. point to an event we have,
+        #   2. has a received_ts from before the cut off, and
+        #   3. we haven't yet censored.
+        #
+        # This is limited to 100 events to ensure that we don't try and do too
+        # much at once. We'll get called again so this should eventually catch
+        # up.
+        sql = """
+            SELECT redactions.event_id, redacts FROM redactions
+            LEFT JOIN events AS original_event ON (
+                redacts = original_event.event_id
+            )
+            WHERE NOT have_censored
+            AND redactions.received_ts <= ?
+            ORDER BY redactions.received_ts ASC
+            LIMIT ?
+        """
+
+        rows = await self.db.execute(
+            "_censor_redactions_fetch", None, sql, before_ts, 100
+        )
+
+        updates = []
+
+        for redaction_id, event_id in rows:
+            redaction_event = await self.get_event(redaction_id, allow_none=True)
+            original_event = await self.get_event(
+                event_id, allow_rejected=True, allow_none=True
+            )
+
+            # The SQL above ensures that we have both the redaction and
+            # original event, so if the `get_event` calls return None it
+            # means that the redaction wasn't allowed. Either way we know that
+            # the result won't change so we mark the fact that we've checked.
+            if (
+                redaction_event
+                and original_event
+                and original_event.internal_metadata.is_redacted()
+            ):
+                # Redaction was allowed
+                pruned_json = encode_json(
+                    prune_event_dict(
+                        original_event.room_version, original_event.get_dict()
+                    )
+                )
+            else:
+                # Redaction wasn't allowed
+                pruned_json = None
+
+            updates.append((redaction_id, event_id, pruned_json))
+
+        def _update_censor_txn(txn):
+            for redaction_id, event_id, pruned_json in updates:
+                if pruned_json:
+                    self._censor_event_txn(txn, event_id, pruned_json)
+
+                self.db.simple_update_one_txn(
+                    txn,
+                    table="redactions",
+                    keyvalues={"event_id": redaction_id},
+                    updatevalues={"have_censored": True},
+                )
+
+        await self.db.runInteraction("_update_censor_txn", _update_censor_txn)
+
+    def _censor_event_txn(self, txn, event_id, pruned_json):
+        """Censor an event by replacing its JSON in the event_json table with the
+        provided pruned JSON.
+
+        Args:
+            txn (LoggingTransaction): The database transaction.
+            event_id (str): The ID of the event to censor.
+            pruned_json (str): The pruned JSON
+        """
+        self.db.simple_update_one_txn(
+            txn,
+            table="event_json",
+            keyvalues={"event_id": event_id},
+            updatevalues={"json": pruned_json},
+        )
+
+    @defer.inlineCallbacks
+    def expire_event(self, event_id):
+        """Retrieve and expire an event that has expired, and delete its associated
+        expiry timestamp. If the event can't be retrieved, delete its associated
+        timestamp so we don't try to expire it again in the future.
+
+        Args:
+             event_id (str): The ID of the event to delete.
+        """
+        # Try to retrieve the event's content from the database or the event cache.
+        event = yield self.get_event(event_id)
+
+        def delete_expired_event_txn(txn):
+            # Delete the expiry timestamp associated with this event from the database.
+            self._delete_event_expiry_txn(txn, event_id)
+
+            if not event:
+                # If we can't find the event, log a warning and delete the expiry date
+                # from the database so that we don't try to expire it again in the
+                # future.
+                logger.warning(
+                    "Can't expire event %s because we don't have it.", event_id
+                )
+                return
+
+            # Prune the event's dict then convert it to JSON.
+            pruned_json = encode_json(
+                prune_event_dict(event.room_version, event.get_dict())
+            )
+
+            # Update the event_json table to replace the event's JSON with the pruned
+            # JSON.
+            self._censor_event_txn(txn, event.event_id, pruned_json)
+
+            # We need to invalidate the event cache entry for this event because we
+            # changed its content in the database. We can't call
+            # self._invalidate_cache_and_stream because self.get_event_cache isn't of the
+            # right type.
+            txn.call_after(self._get_event_cache.invalidate, (event.event_id,))
+            # Send that invalidation to replication so that other workers also invalidate
+            # the event cache.
+            self._send_invalidation_to_replication(
+                txn, "_get_event_cache", (event.event_id,)
+            )
+
+        yield self.db.runInteraction("delete_expired_event", delete_expired_event_txn)
+
+    def _delete_event_expiry_txn(self, txn, event_id):
+        """Delete the expiry timestamp associated with an event ID without deleting the
+        actual event.
+
+        Args:
+            txn (LoggingTransaction): The transaction to use to perform the deletion.
+            event_id (str): The event ID to delete the associated expiry timestamp of.
+        """
+        return self.db.simple_delete_txn(
+            txn=txn, table="event_expiry", keyvalues={"event_id": event_id}
+        )
diff --git a/synapse/storage/data_stores/main/event_federation.py b/synapse/storage/data_stores/main/event_federation.py
index b99439cc37..24ce8c4330 100644
--- a/synapse/storage/data_stores/main/event_federation.py
+++ b/synapse/storage/data_stores/main/event_federation.py
@@ -640,89 +640,6 @@ class EventFederationStore(EventFederationWorkerStore):
             self._delete_old_forward_extrem_cache, 60 * 60 * 1000
         )
 
-    def _update_min_depth_for_room_txn(self, txn, room_id, depth):
-        min_depth = self._get_min_depth_interaction(txn, room_id)
-
-        if min_depth is not None and depth >= min_depth:
-            return
-
-        self.db.simple_upsert_txn(
-            txn,
-            table="room_depth",
-            keyvalues={"room_id": room_id},
-            values={"min_depth": depth},
-        )
-
-    def _handle_mult_prev_events(self, txn, events):
-        """
-        For the given event, update the event edges table and forward and
-        backward extremities tables.
-        """
-        self.db.simple_insert_many_txn(
-            txn,
-            table="event_edges",
-            values=[
-                {
-                    "event_id": ev.event_id,
-                    "prev_event_id": e_id,
-                    "room_id": ev.room_id,
-                    "is_state": False,
-                }
-                for ev in events
-                for e_id in ev.prev_event_ids()
-            ],
-        )
-
-        self._update_backward_extremeties(txn, events)
-
-    def _update_backward_extremeties(self, txn, events):
-        """Updates the event_backward_extremities tables based on the new/updated
-        events being persisted.
-
-        This is called for new events *and* for events that were outliers, but
-        are now being persisted as non-outliers.
-
-        Forward extremities are handled when we first start persisting the events.
-        """
-        events_by_room = {}
-        for ev in events:
-            events_by_room.setdefault(ev.room_id, []).append(ev)
-
-        query = (
-            "INSERT INTO event_backward_extremities (event_id, room_id)"
-            " SELECT ?, ? WHERE NOT EXISTS ("
-            " SELECT 1 FROM event_backward_extremities"
-            " WHERE event_id = ? AND room_id = ?"
-            " )"
-            " AND NOT EXISTS ("
-            " SELECT 1 FROM events WHERE event_id = ? AND room_id = ? "
-            " AND outlier = ?"
-            " )"
-        )
-
-        txn.executemany(
-            query,
-            [
-                (e_id, ev.room_id, e_id, ev.room_id, e_id, ev.room_id, False)
-                for ev in events
-                for e_id in ev.prev_event_ids()
-                if not ev.internal_metadata.is_outlier()
-            ],
-        )
-
-        query = (
-            "DELETE FROM event_backward_extremities"
-            " WHERE event_id = ? AND room_id = ?"
-        )
-        txn.executemany(
-            query,
-            [
-                (ev.event_id, ev.room_id)
-                for ev in events
-                if not ev.internal_metadata.is_outlier()
-            ],
-        )
-
     def _delete_old_forward_extrem_cache(self):
         def _delete_old_forward_extrem_cache_txn(txn):
             # Delete entries older than a month, while making sure we don't delete
diff --git a/synapse/storage/data_stores/main/event_push_actions.py b/synapse/storage/data_stores/main/event_push_actions.py
index 8eed590929..0321274de2 100644
--- a/synapse/storage/data_stores/main/event_push_actions.py
+++ b/synapse/storage/data_stores/main/event_push_actions.py
@@ -652,69 +652,6 @@ class EventPushActionsStore(EventPushActionsWorkerStore):
             self._start_rotate_notifs, 30 * 60 * 1000
         )
 
-    def _set_push_actions_for_event_and_users_txn(
-        self, txn, events_and_contexts, all_events_and_contexts
-    ):
-        """Handles moving push actions from staging table to main
-        event_push_actions table for all events in `events_and_contexts`.
-
-        Also ensures that all events in `all_events_and_contexts` are removed
-        from the push action staging area.
-
-        Args:
-            events_and_contexts (list[(EventBase, EventContext)]): events
-                we are persisting
-            all_events_and_contexts (list[(EventBase, EventContext)]): all
-                events that we were going to persist. This includes events
-                we've already persisted, etc, that wouldn't appear in
-                events_and_context.
-        """
-
-        sql = """
-            INSERT INTO event_push_actions (
-                room_id, event_id, user_id, actions, stream_ordering,
-                topological_ordering, notif, highlight
-            )
-            SELECT ?, event_id, user_id, actions, ?, ?, notif, highlight
-            FROM event_push_actions_staging
-            WHERE event_id = ?
-        """
-
-        if events_and_contexts:
-            txn.executemany(
-                sql,
-                (
-                    (
-                        event.room_id,
-                        event.internal_metadata.stream_ordering,
-                        event.depth,
-                        event.event_id,
-                    )
-                    for event, _ in events_and_contexts
-                ),
-            )
-
-        for event, _ in events_and_contexts:
-            user_ids = self.db.simple_select_onecol_txn(
-                txn,
-                table="event_push_actions_staging",
-                keyvalues={"event_id": event.event_id},
-                retcol="user_id",
-            )
-
-            for uid in user_ids:
-                txn.call_after(
-                    self.get_unread_event_push_actions_by_room_for_user.invalidate_many,
-                    (event.room_id, uid),
-                )
-
-        # Now we delete the staging area for *all* events that were being
-        # persisted.
-        txn.executemany(
-            "DELETE FROM event_push_actions_staging WHERE event_id = ?",
-            ((event.event_id,) for event, _ in all_events_and_contexts),
-        )
-
     @defer.inlineCallbacks
     def get_push_actions_for_user(
         self, user_id, before=None, limit=50, only_highlight=False
@@ -763,17 +700,6 @@ class EventPushActionsStore(EventPushActionsWorkerStore):
         )
         return result[0] or 0
 
-    def _remove_push_actions_for_event_id_txn(self, txn, room_id, event_id):
-        # Sad that we have to blow away the cache for the whole room here
-        txn.call_after(
-            self.get_unread_event_push_actions_by_room_for_user.invalidate_many,
-            (room_id,),
-        )
-        txn.execute(
-            "DELETE FROM event_push_actions WHERE room_id = ? AND event_id = ?",
-            (room_id, event_id),
-        )
-
     def _remove_old_push_actions_before_txn(
         self, txn, room_id, user_id, stream_ordering
     ):
diff --git a/synapse/storage/data_stores/main/events.py b/synapse/storage/data_stores/main/events.py
index e71c23541d..092739962b 100644
--- a/synapse/storage/data_stores/main/events.py
+++ b/synapse/storage/data_stores/main/events.py
@@ -17,39 +17,44 @@
 
 import itertools
 import logging
-from collections import Counter as c_counter, OrderedDict, namedtuple
+from collections import OrderedDict, namedtuple
 from functools import wraps
-from typing import Dict, List, Tuple
+from typing import TYPE_CHECKING, Dict, Iterable, List, Tuple
 
-from six import iteritems, text_type
+from six import integer_types, iteritems, text_type
 from six.moves import range
 
+import attr
 from canonicaljson import json
 from prometheus_client import Counter
 
 from twisted.internet import defer
 
 import synapse.metrics
-from synapse.api.constants import EventContentFields, EventTypes
-from synapse.api.errors import SynapseError
+from synapse.api.constants import (
+    EventContentFields,
+    EventTypes,
+    Membership,
+    RelationTypes,
+)
 from synapse.api.room_versions import RoomVersions
+from synapse.crypto.event_signing import compute_event_reference_hash
 from synapse.events import EventBase  # noqa: F401
 from synapse.events.snapshot import EventContext  # noqa: F401
-from synapse.events.utils import prune_event_dict
 from synapse.logging.utils import log_function
-from synapse.metrics import BucketCollector
-from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage._base import make_in_list_sql_clause
-from synapse.storage.data_stores.main.event_federation import EventFederationStore
-from synapse.storage.data_stores.main.events_worker import EventsWorkerStore
-from synapse.storage.data_stores.main.state import StateGroupWorkerStore
+from synapse.storage.data_stores.main.search import SearchEntry
 from synapse.storage.database import Database, LoggingTransaction
-from synapse.storage.persist_events import DeltaState
-from synapse.types import RoomStreamToken, StateMap, get_domain_from_id
-from synapse.util.caches.descriptors import cached, cachedInlineCallbacks
+from synapse.storage.util.id_generators import StreamIdGenerator
+from synapse.types import StateMap, get_domain_from_id
 from synapse.util.frozenutils import frozendict_json_encoder
 from synapse.util.iterutils import batch_iter
 
+if TYPE_CHECKING:
+    from synapse.storage.data_stores.main import DataStore
+    from synapse.server import HomeServer
+
+
 logger = logging.getLogger(__name__)
 
 persist_event_counter = Counter("synapse_storage_events_persisted_events", "")
@@ -94,58 +99,49 @@ def _retry_on_integrity_error(func):
     return f
 
 
-# inherits from EventFederationStore so that we can call _update_backward_extremities
-# and _handle_mult_prev_events (though arguably those could both be moved in here)
-class EventsStore(
-    StateGroupWorkerStore, EventFederationStore, EventsWorkerStore,
-):
-    def __init__(self, database: Database, db_conn, hs):
-        super(EventsStore, self).__init__(database, db_conn, hs)
+@attr.s(slots=True)
+class DeltaState:
+    """Deltas to use to update the `current_state_events` table.
 
-        # Collect metrics on the number of forward extremities that exist.
-        # Counter of number of extremities to count
-        self._current_forward_extremities_amount = c_counter()
+    Attributes:
+        to_delete: List of type/state_keys to delete from current state
+        to_insert: Map of state to upsert into current state
+        no_longer_in_room: The server is not longer in the room, so the room
+            should e.g. be removed from `current_state_events` table.
+    """
 
-        BucketCollector(
-            "synapse_forward_extremities",
-            lambda: self._current_forward_extremities_amount,
-            buckets=[1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"],
-        )
+    to_delete = attr.ib(type=List[Tuple[str, str]])
+    to_insert = attr.ib(type=StateMap[str])
+    no_longer_in_room = attr.ib(type=bool, default=False)
 
-        # Read the extrems every 60 minutes
-        def read_forward_extremities():
-            # run as a background process to make sure that the database transactions
-            # have a logcontext to report to
-            return run_as_background_process(
-                "read_forward_extremities", self._read_forward_extremities
-            )
 
-        hs.get_clock().looping_call(read_forward_extremities, 60 * 60 * 1000)
+class PersistEventsStore:
+    """Contains all the functions for writing events to the database.
 
-        def _censor_redactions():
-            return run_as_background_process(
-                "_censor_redactions", self._censor_redactions
-            )
+    Should only be instansiated on one process (when using a worker mode setup).
+
+    Note: This is not part of the `DataStore` mixin.
+    """
 
-        if self.hs.config.redaction_retention_period is not None:
-            hs.get_clock().looping_call(_censor_redactions, 5 * 60 * 1000)
+    def __init__(self, hs: "HomeServer", db: Database, main_data_store: "DataStore"):
+        self.hs = hs
+        self.db = db
+        self.store = main_data_store
+        self.database_engine = db.engine
+        self._clock = hs.get_clock()
 
         self._ephemeral_messages_enabled = hs.config.enable_ephemeral_messages
         self.is_mine_id = hs.is_mine_id
 
-    @defer.inlineCallbacks
-    def _read_forward_extremities(self):
-        def fetch(txn):
-            txn.execute(
-                """
-                select count(*) c from event_forward_extremities
-                group by room_id
-                """
-            )
-            return txn.fetchall()
+        # Ideally we'd move these ID gens here, unfortunately some other ID
+        # generators are chained off them so doing so is a bit of a PITA.
+        self._backfill_id_gen = self.store._backfill_id_gen  # type: StreamIdGenerator
+        self._stream_id_gen = self.store._stream_id_gen  # type: StreamIdGenerator
 
-        res = yield self.db.runInteraction("read_forward_extremities", fetch)
-        self._current_forward_extremities_amount = c_counter([x[0] for x in res])
+        # This should only exist on master for now
+        assert (
+            hs.config.worker.worker_app is None
+        ), "Can only instantiate PersistEventsStore on master"
 
     @_retry_on_integrity_error
     @defer.inlineCallbacks
@@ -237,10 +233,10 @@ class EventsStore(
                 event_counter.labels(event.type, origin_type, origin_entity).inc()
 
             for room_id, new_state in iteritems(current_state_for_room):
-                self.get_current_state_ids.prefill((room_id,), new_state)
+                self.store.get_current_state_ids.prefill((room_id,), new_state)
 
             for room_id, latest_event_ids in iteritems(new_forward_extremeties):
-                self.get_latest_event_ids_in_room.prefill(
+                self.store.get_latest_event_ids_in_room.prefill(
                     (room_id,), list(latest_event_ids)
                 )
 
@@ -586,7 +582,7 @@ class EventsStore(
                 )
 
             txn.call_after(
-                self._curr_state_delta_stream_cache.entity_has_changed,
+                self.store._curr_state_delta_stream_cache.entity_has_changed,
                 room_id,
                 stream_id,
             )
@@ -606,10 +602,13 @@ class EventsStore(
 
             for member in members_changed:
                 txn.call_after(
-                    self.get_rooms_for_user_with_stream_ordering.invalidate, (member,)
+                    self.store.get_rooms_for_user_with_stream_ordering.invalidate,
+                    (member,),
                 )
 
-            self._invalidate_state_caches_and_stream(txn, room_id, members_changed)
+            self.store._invalidate_state_caches_and_stream(
+                txn, room_id, members_changed
+            )
 
     def _upsert_room_version_txn(self, txn: LoggingTransaction, room_id: str):
         """Update the room version in the database based off current state
@@ -647,7 +646,9 @@ class EventsStore(
             self.db.simple_delete_txn(
                 txn, table="event_forward_extremities", keyvalues={"room_id": room_id}
             )
-            txn.call_after(self.get_latest_event_ids_in_room.invalidate, (room_id,))
+            txn.call_after(
+                self.store.get_latest_event_ids_in_room.invalidate, (room_id,)
+            )
 
         self.db.simple_insert_many_txn(
             txn,
@@ -713,10 +714,10 @@ class EventsStore(
         depth_updates = {}
         for event, context in events_and_contexts:
             # Remove the any existing cache entries for the event_ids
-            txn.call_after(self._invalidate_get_event_cache, event.event_id)
+            txn.call_after(self.store._invalidate_get_event_cache, event.event_id)
             if not backfilled:
                 txn.call_after(
-                    self._events_stream_cache.entity_has_changed,
+                    self.store._events_stream_cache.entity_has_changed,
                     event.room_id,
                     event.internal_metadata.stream_ordering,
                 )
@@ -1088,13 +1089,15 @@ class EventsStore(
 
         def prefill():
             for cache_entry in to_prefill:
-                self._get_event_cache.prefill((cache_entry[0].event_id,), cache_entry)
+                self.store._get_event_cache.prefill(
+                    (cache_entry[0].event_id,), cache_entry
+                )
 
         txn.call_after(prefill)
 
     def _store_redaction(self, txn, event):
         # invalidate the cache for the redacted event
-        txn.call_after(self._invalidate_get_event_cache, event.redacts)
+        txn.call_after(self.store._invalidate_get_event_cache, event.redacts)
 
         self.db.simple_insert_txn(
             txn,
@@ -1106,783 +1109,484 @@ class EventsStore(
             },
         )
 
-    async def _censor_redactions(self):
-        """Censors all redactions older than the configured period that haven't
-        been censored yet.
+    def insert_labels_for_event_txn(
+        self, txn, event_id, labels, room_id, topological_ordering
+    ):
+        """Store the mapping between an event's ID and its labels, with one row per
+        (event_id, label) tuple.
 
-        By censor we mean update the event_json table with the redacted event.
+        Args:
+            txn (LoggingTransaction): The transaction to execute.
+            event_id (str): The event's ID.
+            labels (list[str]): A list of text labels.
+            room_id (str): The ID of the room the event was sent to.
+            topological_ordering (int): The position of the event in the room's topology.
         """
+        return self.db.simple_insert_many_txn(
+            txn=txn,
+            table="event_labels",
+            values=[
+                {
+                    "event_id": event_id,
+                    "label": label,
+                    "room_id": room_id,
+                    "topological_ordering": topological_ordering,
+                }
+                for label in labels
+            ],
+        )
 
-        if self.hs.config.redaction_retention_period is None:
-            return
-
-        if not (
-            await self.db.updates.has_completed_background_update(
-                "redactions_have_censored_ts_idx"
-            )
-        ):
-            # We don't want to run this until the appropriate index has been
-            # created.
-            return
-
-        before_ts = self._clock.time_msec() - self.hs.config.redaction_retention_period
+    def _insert_event_expiry_txn(self, txn, event_id, expiry_ts):
+        """Save the expiry timestamp associated with a given event ID.
 
-        # We fetch all redactions that:
-        #   1. point to an event we have,
-        #   2. has a received_ts from before the cut off, and
-        #   3. we haven't yet censored.
-        #
-        # This is limited to 100 events to ensure that we don't try and do too
-        # much at once. We'll get called again so this should eventually catch
-        # up.
-        sql = """
-            SELECT redactions.event_id, redacts FROM redactions
-            LEFT JOIN events AS original_event ON (
-                redacts = original_event.event_id
-            )
-            WHERE NOT have_censored
-            AND redactions.received_ts <= ?
-            ORDER BY redactions.received_ts ASC
-            LIMIT ?
+        Args:
+            txn (LoggingTransaction): The database transaction to use.
+            event_id (str): The event ID the expiry timestamp is associated with.
+            expiry_ts (int): The timestamp at which to expire (delete) the event.
         """
-
-        rows = await self.db.execute(
-            "_censor_redactions_fetch", None, sql, before_ts, 100
+        return self.db.simple_insert_txn(
+            txn=txn,
+            table="event_expiry",
+            values={"event_id": event_id, "expiry_ts": expiry_ts},
         )
 
-        updates = []
+    def _store_event_reference_hashes_txn(self, txn, events):
+        """Store a hash for a PDU
+        Args:
+            txn (cursor):
+            events (list): list of Events.
+        """
 
-        for redaction_id, event_id in rows:
-            redaction_event = await self.get_event(redaction_id, allow_none=True)
-            original_event = await self.get_event(
-                event_id, allow_rejected=True, allow_none=True
+        vals = []
+        for event in events:
+            ref_alg, ref_hash_bytes = compute_event_reference_hash(event)
+            vals.append(
+                {
+                    "event_id": event.event_id,
+                    "algorithm": ref_alg,
+                    "hash": memoryview(ref_hash_bytes),
+                }
             )
 
-            # The SQL above ensures that we have both the redaction and
-            # original event, so if the `get_event` calls return None it
-            # means that the redaction wasn't allowed. Either way we know that
-            # the result won't change so we mark the fact that we've checked.
-            if (
-                redaction_event
-                and original_event
-                and original_event.internal_metadata.is_redacted()
-            ):
-                # Redaction was allowed
-                pruned_json = encode_json(
-                    prune_event_dict(
-                        original_event.room_version, original_event.get_dict()
-                    )
-                )
-            else:
-                # Redaction wasn't allowed
-                pruned_json = None
-
-            updates.append((redaction_id, event_id, pruned_json))
-
-        def _update_censor_txn(txn):
-            for redaction_id, event_id, pruned_json in updates:
-                if pruned_json:
-                    self._censor_event_txn(txn, event_id, pruned_json)
-
-                self.db.simple_update_one_txn(
-                    txn,
-                    table="redactions",
-                    keyvalues={"event_id": redaction_id},
-                    updatevalues={"have_censored": True},
-                )
-
-        await self.db.runInteraction("_update_censor_txn", _update_censor_txn)
+        self.db.simple_insert_many_txn(txn, table="event_reference_hashes", values=vals)
 
-    def _censor_event_txn(self, txn, event_id, pruned_json):
-        """Censor an event by replacing its JSON in the event_json table with the
-        provided pruned JSON.
-
-        Args:
-            txn (LoggingTransaction): The database transaction.
-            event_id (str): The ID of the event to censor.
-            pruned_json (str): The pruned JSON
+    def _store_room_members_txn(self, txn, events, backfilled):
+        """Store a room member in the database.
         """
-        self.db.simple_update_one_txn(
+        self.db.simple_insert_many_txn(
             txn,
-            table="event_json",
-            keyvalues={"event_id": event_id},
-            updatevalues={"json": pruned_json},
+            table="room_memberships",
+            values=[
+                {
+                    "event_id": event.event_id,
+                    "user_id": event.state_key,
+                    "sender": event.user_id,
+                    "room_id": event.room_id,
+                    "membership": event.membership,
+                    "display_name": event.content.get("displayname", None),
+                    "avatar_url": event.content.get("avatar_url", None),
+                }
+                for event in events
+            ],
         )
 
-    @defer.inlineCallbacks
-    def count_daily_messages(self):
-        """
-        Returns an estimate of the number of messages sent in the last day.
-
-        If it has been significantly less or more than one day since the last
-        call to this function, it will return None.
-        """
-
-        def _count_messages(txn):
-            sql = """
-                SELECT COALESCE(COUNT(*), 0) FROM events
-                WHERE type = 'm.room.message'
-                AND stream_ordering > ?
-            """
-            txn.execute(sql, (self.stream_ordering_day_ago,))
-            (count,) = txn.fetchone()
-            return count
-
-        ret = yield self.db.runInteraction("count_messages", _count_messages)
-        return ret
-
-    @defer.inlineCallbacks
-    def count_daily_sent_messages(self):
-        def _count_messages(txn):
-            # This is good enough as if you have silly characters in your own
-            # hostname then thats your own fault.
-            like_clause = "%:" + self.hs.hostname
-
-            sql = """
-                SELECT COALESCE(COUNT(*), 0) FROM events
-                WHERE type = 'm.room.message'
-                    AND sender LIKE ?
-                AND stream_ordering > ?
-            """
-
-            txn.execute(sql, (like_clause, self.stream_ordering_day_ago))
-            (count,) = txn.fetchone()
-            return count
-
-        ret = yield self.db.runInteraction("count_daily_sent_messages", _count_messages)
-        return ret
-
-    @defer.inlineCallbacks
-    def count_daily_active_rooms(self):
-        def _count(txn):
-            sql = """
-                SELECT COALESCE(COUNT(DISTINCT room_id), 0) FROM events
-                WHERE type = 'm.room.message'
-                AND stream_ordering > ?
-            """
-            txn.execute(sql, (self.stream_ordering_day_ago,))
-            (count,) = txn.fetchone()
-            return count
-
-        ret = yield self.db.runInteraction("count_daily_active_rooms", _count)
-        return ret
-
-    @cached(num_args=5, max_entries=10)
-    def get_all_new_events(
-        self,
-        last_backfill_id,
-        last_forward_id,
-        current_backfill_id,
-        current_forward_id,
-        limit,
-    ):
-        """Get all the new events that have arrived at the server either as
-        new events or as backfilled events"""
-        have_backfill_events = last_backfill_id != current_backfill_id
-        have_forward_events = last_forward_id != current_forward_id
-
-        if not have_backfill_events and not have_forward_events:
-            return defer.succeed(AllNewEventsResult([], [], [], [], []))
-
-        def get_all_new_events_txn(txn):
-            sql = (
-                "SELECT e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
-                " FROM events AS e"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " WHERE ? < stream_ordering AND stream_ordering <= ?"
-                " ORDER BY stream_ordering ASC"
-                " LIMIT ?"
+        for event in events:
+            txn.call_after(
+                self.store._membership_stream_cache.entity_has_changed,
+                event.state_key,
+                event.internal_metadata.stream_ordering,
             )
-            if have_forward_events:
-                txn.execute(sql, (last_forward_id, current_forward_id, limit))
-                new_forward_events = txn.fetchall()
-
-                if len(new_forward_events) == limit:
-                    upper_bound = new_forward_events[-1][0]
-                else:
-                    upper_bound = current_forward_id
-
-                sql = (
-                    "SELECT event_stream_ordering, event_id, state_group"
-                    " FROM ex_outlier_stream"
-                    " WHERE ? > event_stream_ordering"
-                    " AND event_stream_ordering >= ?"
-                    " ORDER BY event_stream_ordering DESC"
-                )
-                txn.execute(sql, (last_forward_id, upper_bound))
-                forward_ex_outliers = txn.fetchall()
-            else:
-                new_forward_events = []
-                forward_ex_outliers = []
-
-            sql = (
-                "SELECT -e.stream_ordering, e.event_id, e.room_id, e.type,"
-                " state_key, redacts"
-                " FROM events AS e"
-                " LEFT JOIN redactions USING (event_id)"
-                " LEFT JOIN state_events USING (event_id)"
-                " WHERE ? > stream_ordering AND stream_ordering >= ?"
-                " ORDER BY stream_ordering DESC"
-                " LIMIT ?"
+            txn.call_after(
+                self.store.get_invited_rooms_for_local_user.invalidate,
+                (event.state_key,),
             )
-            if have_backfill_events:
-                txn.execute(sql, (-last_backfill_id, -current_backfill_id, limit))
-                new_backfill_events = txn.fetchall()
 
-                if len(new_backfill_events) == limit:
-                    upper_bound = new_backfill_events[-1][0]
-                else:
-                    upper_bound = current_backfill_id
-
-                sql = (
-                    "SELECT -event_stream_ordering, event_id, state_group"
-                    " FROM ex_outlier_stream"
-                    " WHERE ? > event_stream_ordering"
-                    " AND event_stream_ordering >= ?"
-                    " ORDER BY event_stream_ordering DESC"
-                )
-                txn.execute(sql, (-last_backfill_id, -upper_bound))
-                backward_ex_outliers = txn.fetchall()
-            else:
-                new_backfill_events = []
-                backward_ex_outliers = []
-
-            return AllNewEventsResult(
-                new_forward_events,
-                new_backfill_events,
-                forward_ex_outliers,
-                backward_ex_outliers,
+            # We update the local_invites table only if the event is "current",
+            # i.e., its something that has just happened. If the event is an
+            # outlier it is only current if its an "out of band membership",
+            # like a remote invite or a rejection of a remote invite.
+            is_new_state = not backfilled and (
+                not event.internal_metadata.is_outlier()
+                or event.internal_metadata.is_out_of_band_membership()
             )
+            is_mine = self.is_mine_id(event.state_key)
+            if is_new_state and is_mine:
+                if event.membership == Membership.INVITE:
+                    self.db.simple_insert_txn(
+                        txn,
+                        table="local_invites",
+                        values={
+                            "event_id": event.event_id,
+                            "invitee": event.state_key,
+                            "inviter": event.sender,
+                            "room_id": event.room_id,
+                            "stream_id": event.internal_metadata.stream_ordering,
+                        },
+                    )
+                else:
+                    sql = (
+                        "UPDATE local_invites SET stream_id = ?, replaced_by = ? WHERE"
+                        " room_id = ? AND invitee = ? AND locally_rejected is NULL"
+                        " AND replaced_by is NULL"
+                    )
 
-        return self.db.runInteraction("get_all_new_events", get_all_new_events_txn)
-
-    def purge_history(self, room_id, token, delete_local_events):
-        """Deletes room history before a certain point
-
-        Args:
-            room_id (str):
+                    txn.execute(
+                        sql,
+                        (
+                            event.internal_metadata.stream_ordering,
+                            event.event_id,
+                            event.room_id,
+                            event.state_key,
+                        ),
+                    )
 
-            token (str): A topological token to delete events before
+                # We also update the `local_current_membership` table with
+                # latest invite info. This will usually get updated by the
+                # `current_state_events` handling, unless its an outlier.
+                if event.internal_metadata.is_outlier():
+                    # This should only happen for out of band memberships, so
+                    # we add a paranoia check.
+                    assert event.internal_metadata.is_out_of_band_membership()
+
+                    self.db.simple_upsert_txn(
+                        txn,
+                        table="local_current_membership",
+                        keyvalues={
+                            "room_id": event.room_id,
+                            "user_id": event.state_key,
+                        },
+                        values={
+                            "event_id": event.event_id,
+                            "membership": event.membership,
+                        },
+                    )
 
-            delete_local_events (bool):
-                if True, we will delete local events as well as remote ones
-                (instead of just marking them as outliers and deleting their
-                state groups).
+    def _handle_event_relations(self, txn, event):
+        """Handles inserting relation data during peristence of events
 
-        Returns:
-            Deferred[set[int]]: The set of state groups that are referenced by
-            deleted events.
+        Args:
+            txn
+            event (EventBase)
         """
+        relation = event.content.get("m.relates_to")
+        if not relation:
+            # No relations
+            return
 
-        return self.db.runInteraction(
-            "purge_history",
-            self._purge_history_txn,
-            room_id,
-            token,
-            delete_local_events,
-        )
+        rel_type = relation.get("rel_type")
+        if rel_type not in (
+            RelationTypes.ANNOTATION,
+            RelationTypes.REFERENCE,
+            RelationTypes.REPLACE,
+        ):
+            # Unknown relation type
+            return
 
-    def _purge_history_txn(self, txn, room_id, token_str, delete_local_events):
-        token = RoomStreamToken.parse(token_str)
-
-        # Tables that should be pruned:
-        #     event_auth
-        #     event_backward_extremities
-        #     event_edges
-        #     event_forward_extremities
-        #     event_json
-        #     event_push_actions
-        #     event_reference_hashes
-        #     event_search
-        #     event_to_state_groups
-        #     events
-        #     rejections
-        #     room_depth
-        #     state_groups
-        #     state_groups_state
-
-        # we will build a temporary table listing the events so that we don't
-        # have to keep shovelling the list back and forth across the
-        # connection. Annoyingly the python sqlite driver commits the
-        # transaction on CREATE, so let's do this first.
-        #
-        # furthermore, we might already have the table from a previous (failed)
-        # purge attempt, so let's drop the table first.
+        parent_id = relation.get("event_id")
+        if not parent_id:
+            # Invalid relation
+            return
 
-        txn.execute("DROP TABLE IF EXISTS events_to_purge")
+        aggregation_key = relation.get("key")
 
-        txn.execute(
-            "CREATE TEMPORARY TABLE events_to_purge ("
-            "    event_id TEXT NOT NULL,"
-            "    should_delete BOOLEAN NOT NULL"
-            ")"
+        self.db.simple_insert_txn(
+            txn,
+            table="event_relations",
+            values={
+                "event_id": event.event_id,
+                "relates_to_id": parent_id,
+                "relation_type": rel_type,
+                "aggregation_key": aggregation_key,
+            },
         )
 
-        # First ensure that we're not about to delete all the forward extremeties
-        txn.execute(
-            "SELECT e.event_id, e.depth FROM events as e "
-            "INNER JOIN event_forward_extremities as f "
-            "ON e.event_id = f.event_id "
-            "AND e.room_id = f.room_id "
-            "WHERE f.room_id = ?",
-            (room_id,),
+        txn.call_after(self.store.get_relations_for_event.invalidate_many, (parent_id,))
+        txn.call_after(
+            self.store.get_aggregation_groups_for_event.invalidate_many, (parent_id,)
         )
-        rows = txn.fetchall()
-        max_depth = max(row[1] for row in rows)
-
-        if max_depth < token.topological:
-            # We need to ensure we don't delete all the events from the database
-            # otherwise we wouldn't be able to send any events (due to not
-            # having any backwards extremeties)
-            raise SynapseError(
-                400, "topological_ordering is greater than forward extremeties"
-            )
-
-        logger.info("[purge] looking for events to delete")
-
-        should_delete_expr = "state_key IS NULL"
-        should_delete_params = ()
-        if not delete_local_events:
-            should_delete_expr += " AND event_id NOT LIKE ?"
-
-            # We include the parameter twice since we use the expression twice
-            should_delete_params += ("%:" + self.hs.hostname, "%:" + self.hs.hostname)
 
-        should_delete_params += (room_id, token.topological)
+        if rel_type == RelationTypes.REPLACE:
+            txn.call_after(self.store.get_applicable_edit.invalidate, (parent_id,))
 
-        # Note that we insert events that are outliers and aren't going to be
-        # deleted, as nothing will happen to them.
-        txn.execute(
-            "INSERT INTO events_to_purge"
-            " SELECT event_id, %s"
-            " FROM events AS e LEFT JOIN state_events USING (event_id)"
-            " WHERE (NOT outlier OR (%s)) AND e.room_id = ? AND topological_ordering < ?"
-            % (should_delete_expr, should_delete_expr),
-            should_delete_params,
-        )
+    def _handle_redaction(self, txn, redacted_event_id):
+        """Handles receiving a redaction and checking whether we need to remove
+        any redacted relations from the database.
 
-        # We create the indices *after* insertion as that's a lot faster.
+        Args:
+            txn
+            redacted_event_id (str): The event that was redacted.
+        """
 
-        # create an index on should_delete because later we'll be looking for
-        # the should_delete / shouldn't_delete subsets
-        txn.execute(
-            "CREATE INDEX events_to_purge_should_delete"
-            " ON events_to_purge(should_delete)"
+        self.db.simple_delete_txn(
+            txn, table="event_relations", keyvalues={"event_id": redacted_event_id}
         )
 
-        # We do joins against events_to_purge for e.g. calculating state
-        # groups to purge, etc., so lets make an index.
-        txn.execute("CREATE INDEX events_to_purge_id ON events_to_purge(event_id)")
-
-        txn.execute("SELECT event_id, should_delete FROM events_to_purge")
-        event_rows = txn.fetchall()
-        logger.info(
-            "[purge] found %i events before cutoff, of which %i can be deleted",
-            len(event_rows),
-            sum(1 for e in event_rows if e[1]),
-        )
+    def _store_room_topic_txn(self, txn, event):
+        if hasattr(event, "content") and "topic" in event.content:
+            self.store_event_search_txn(
+                txn, event, "content.topic", event.content["topic"]
+            )
 
-        logger.info("[purge] Finding new backward extremities")
+    def _store_room_name_txn(self, txn, event):
+        if hasattr(event, "content") and "name" in event.content:
+            self.store_event_search_txn(
+                txn, event, "content.name", event.content["name"]
+            )
 
-        # We calculate the new entries for the backward extremeties by finding
-        # events to be purged that are pointed to by events we're not going to
-        # purge.
-        txn.execute(
-            "SELECT DISTINCT e.event_id FROM events_to_purge AS e"
-            " INNER JOIN event_edges AS ed ON e.event_id = ed.prev_event_id"
-            " LEFT JOIN events_to_purge AS ep2 ON ed.event_id = ep2.event_id"
-            " WHERE ep2.event_id IS NULL"
-        )
-        new_backwards_extrems = txn.fetchall()
+    def _store_room_message_txn(self, txn, event):
+        if hasattr(event, "content") and "body" in event.content:
+            self.store_event_search_txn(
+                txn, event, "content.body", event.content["body"]
+            )
 
-        logger.info("[purge] replacing backward extremities: %r", new_backwards_extrems)
+    def _store_retention_policy_for_room_txn(self, txn, event):
+        if hasattr(event, "content") and (
+            "min_lifetime" in event.content or "max_lifetime" in event.content
+        ):
+            if (
+                "min_lifetime" in event.content
+                and not isinstance(event.content.get("min_lifetime"), integer_types)
+            ) or (
+                "max_lifetime" in event.content
+                and not isinstance(event.content.get("max_lifetime"), integer_types)
+            ):
+                # Ignore the event if one of the value isn't an integer.
+                return
 
-        txn.execute(
-            "DELETE FROM event_backward_extremities WHERE room_id = ?", (room_id,)
-        )
+            self.db.simple_insert_txn(
+                txn=txn,
+                table="room_retention",
+                values={
+                    "room_id": event.room_id,
+                    "event_id": event.event_id,
+                    "min_lifetime": event.content.get("min_lifetime"),
+                    "max_lifetime": event.content.get("max_lifetime"),
+                },
+            )
 
-        # Update backward extremeties
-        txn.executemany(
-            "INSERT INTO event_backward_extremities (room_id, event_id)"
-            " VALUES (?, ?)",
-            [(room_id, event_id) for event_id, in new_backwards_extrems],
-        )
+            self.store._invalidate_cache_and_stream(
+                txn, self.store.get_retention_policy_for_room, (event.room_id,)
+            )
 
-        logger.info("[purge] finding state groups referenced by deleted events")
+    def store_event_search_txn(self, txn, event, key, value):
+        """Add event to the search table
 
-        # Get all state groups that are referenced by events that are to be
-        # deleted.
-        txn.execute(
-            """
-            SELECT DISTINCT state_group FROM events_to_purge
-            INNER JOIN event_to_state_groups USING (event_id)
+        Args:
+            txn (cursor):
+            event (EventBase):
+            key (str):
+            value (str):
         """
+        self.store.store_search_entries_txn(
+            txn,
+            (
+                SearchEntry(
+                    key=key,
+                    value=value,
+                    event_id=event.event_id,
+                    room_id=event.room_id,
+                    stream_ordering=event.internal_metadata.stream_ordering,
+                    origin_server_ts=event.origin_server_ts,
+                ),
+            ),
         )
 
-        referenced_state_groups = {sg for sg, in txn}
-        logger.info(
-            "[purge] found %i referenced state groups", len(referenced_state_groups)
-        )
+    def _set_push_actions_for_event_and_users_txn(
+        self, txn, events_and_contexts, all_events_and_contexts
+    ):
+        """Handles moving push actions from staging table to main
+        event_push_actions table for all events in `events_and_contexts`.
 
-        logger.info("[purge] removing events from event_to_state_groups")
-        txn.execute(
-            "DELETE FROM event_to_state_groups "
-            "WHERE event_id IN (SELECT event_id from events_to_purge)"
-        )
-        for event_id, _ in event_rows:
-            txn.call_after(self._get_state_group_for_event.invalidate, (event_id,))
+        Also ensures that all events in `all_events_and_contexts` are removed
+        from the push action staging area.
 
-        # Delete all remote non-state events
-        for table in (
-            "events",
-            "event_json",
-            "event_auth",
-            "event_edges",
-            "event_forward_extremities",
-            "event_reference_hashes",
-            "event_search",
-            "rejections",
-        ):
-            logger.info("[purge] removing events from %s", table)
+        Args:
+            events_and_contexts (list[(EventBase, EventContext)]): events
+                we are persisting
+            all_events_and_contexts (list[(EventBase, EventContext)]): all
+                events that we were going to persist. This includes events
+                we've already persisted, etc, that wouldn't appear in
+                events_and_context.
+        """
 
-            txn.execute(
-                "DELETE FROM %s WHERE event_id IN ("
-                "    SELECT event_id FROM events_to_purge WHERE should_delete"
-                ")" % (table,)
+        sql = """
+            INSERT INTO event_push_actions (
+                room_id, event_id, user_id, actions, stream_ordering,
+                topological_ordering, notif, highlight
             )
+            SELECT ?, event_id, user_id, actions, ?, ?, notif, highlight
+            FROM event_push_actions_staging
+            WHERE event_id = ?
+        """
 
-        # event_push_actions lacks an index on event_id, and has one on
-        # (room_id, event_id) instead.
-        for table in ("event_push_actions",):
-            logger.info("[purge] removing events from %s", table)
+        if events_and_contexts:
+            txn.executemany(
+                sql,
+                (
+                    (
+                        event.room_id,
+                        event.internal_metadata.stream_ordering,
+                        event.depth,
+                        event.event_id,
+                    )
+                    for event, _ in events_and_contexts
+                ),
+            )
 
-            txn.execute(
-                "DELETE FROM %s WHERE room_id = ? AND event_id IN ("
-                "    SELECT event_id FROM events_to_purge WHERE should_delete"
-                ")" % (table,),
-                (room_id,),
+        for event, _ in events_and_contexts:
+            user_ids = self.db.simple_select_onecol_txn(
+                txn,
+                table="event_push_actions_staging",
+                keyvalues={"event_id": event.event_id},
+                retcol="user_id",
             )
 
-        # Mark all state and own events as outliers
-        logger.info("[purge] marking remaining events as outliers")
-        txn.execute(
-            "UPDATE events SET outlier = ?"
-            " WHERE event_id IN ("
-            "    SELECT event_id FROM events_to_purge "
-            "    WHERE NOT should_delete"
-            ")",
-            (True,),
+            for uid in user_ids:
+                txn.call_after(
+                    self.store.get_unread_event_push_actions_by_room_for_user.invalidate_many,
+                    (event.room_id, uid),
+                )
+
+        # Now we delete the staging area for *all* events that were being
+        # persisted.
+        txn.executemany(
+            "DELETE FROM event_push_actions_staging WHERE event_id = ?",
+            ((event.event_id,) for event, _ in all_events_and_contexts),
         )
 
-        # synapse tries to take out an exclusive lock on room_depth whenever it
-        # persists events (because upsert), and once we run this update, we
-        # will block that for the rest of our transaction.
-        #
-        # So, let's stick it at the end so that we don't block event
-        # persistence.
-        #
-        # We do this by calculating the minimum depth of the backwards
-        # extremities. However, the events in event_backward_extremities
-        # are ones we don't have yet so we need to look at the events that
-        # point to it via event_edges table.
-        txn.execute(
-            """
-            SELECT COALESCE(MIN(depth), 0)
-            FROM event_backward_extremities AS eb
-            INNER JOIN event_edges AS eg ON eg.prev_event_id = eb.event_id
-            INNER JOIN events AS e ON e.event_id = eg.event_id
-            WHERE eb.room_id = ?
-        """,
+    def _remove_push_actions_for_event_id_txn(self, txn, room_id, event_id):
+        # Sad that we have to blow away the cache for the whole room here
+        txn.call_after(
+            self.store.get_unread_event_push_actions_by_room_for_user.invalidate_many,
             (room_id,),
         )
-        (min_depth,) = txn.fetchone()
-
-        logger.info("[purge] updating room_depth to %d", min_depth)
-
         txn.execute(
-            "UPDATE room_depth SET min_depth = ? WHERE room_id = ?",
-            (min_depth, room_id),
+            "DELETE FROM event_push_actions WHERE room_id = ? AND event_id = ?",
+            (room_id, event_id),
         )
 
-        # finally, drop the temp table. this will commit the txn in sqlite,
-        # so make sure to keep this actually last.
-        txn.execute("DROP TABLE events_to_purge")
-
-        logger.info("[purge] done")
-
-        return referenced_state_groups
-
-    def purge_room(self, room_id):
-        """Deletes all record of a room
+    def _store_rejections_txn(self, txn, event_id, reason):
+        self.db.simple_insert_txn(
+            txn,
+            table="rejections",
+            values={
+                "event_id": event_id,
+                "reason": reason,
+                "last_check": self._clock.time_msec(),
+            },
+        )
 
-        Args:
-            room_id (str)
+    def _store_event_state_mappings_txn(
+        self, txn, events_and_contexts: Iterable[Tuple[EventBase, EventContext]]
+    ):
+        state_groups = {}
+        for event, context in events_and_contexts:
+            if event.internal_metadata.is_outlier():
+                continue
 
-        Returns:
-            Deferred[List[int]]: The list of state groups to delete.
-        """
+            # if the event was rejected, just give it the same state as its
+            # predecessor.
+            if context.rejected:
+                state_groups[event.event_id] = context.state_group_before_event
+                continue
 
-        return self.db.runInteraction("purge_room", self._purge_room_txn, room_id)
+            state_groups[event.event_id] = context.state_group
 
-    def _purge_room_txn(self, txn, room_id):
-        # First we fetch all the state groups that should be deleted, before
-        # we delete that information.
-        txn.execute(
-            """
-                SELECT DISTINCT state_group FROM events
-                INNER JOIN event_to_state_groups USING(event_id)
-                WHERE events.room_id = ?
-            """,
-            (room_id,),
+        self.db.simple_insert_many_txn(
+            txn,
+            table="event_to_state_groups",
+            values=[
+                {"state_group": state_group_id, "event_id": event_id}
+                for event_id, state_group_id in iteritems(state_groups)
+            ],
         )
 
-        state_groups = [row[0] for row in txn]
-
-        # Now we delete tables which lack an index on room_id but have one on event_id
-        for table in (
-            "event_auth",
-            "event_edges",
-            "event_push_actions_staging",
-            "event_reference_hashes",
-            "event_relations",
-            "event_to_state_groups",
-            "redactions",
-            "rejections",
-            "state_events",
-        ):
-            logger.info("[purge] removing %s from %s", room_id, table)
-
-            txn.execute(
-                """
-                DELETE FROM %s WHERE event_id IN (
-                  SELECT event_id FROM events WHERE room_id=?
-                )
-                """
-                % (table,),
-                (room_id,),
+        for event_id, state_group_id in iteritems(state_groups):
+            txn.call_after(
+                self.store._get_state_group_for_event.prefill,
+                (event_id,),
+                state_group_id,
             )
 
-        # and finally, the tables with an index on room_id (or no useful index)
-        for table in (
-            "current_state_events",
-            "event_backward_extremities",
-            "event_forward_extremities",
-            "event_json",
-            "event_push_actions",
-            "event_search",
-            "events",
-            "group_rooms",
-            "public_room_list_stream",
-            "receipts_graph",
-            "receipts_linearized",
-            "room_aliases",
-            "room_depth",
-            "room_memberships",
-            "room_stats_state",
-            "room_stats_current",
-            "room_stats_historical",
-            "room_stats_earliest_token",
-            "rooms",
-            "stream_ordering_to_exterm",
-            "users_in_public_rooms",
-            "users_who_share_private_rooms",
-            # no useful index, but let's clear them anyway
-            "appservice_room_list",
-            "e2e_room_keys",
-            "event_push_summary",
-            "pusher_throttle",
-            "group_summary_rooms",
-            "local_invites",
-            "room_account_data",
-            "room_tags",
-            "local_current_membership",
-        ):
-            logger.info("[purge] removing %s from %s", room_id, table)
-            txn.execute("DELETE FROM %s WHERE room_id=?" % (table,), (room_id,))
-
-        # Other tables we do NOT need to clear out:
-        #
-        #  - blocked_rooms
-        #    This is important, to make sure that we don't accidentally rejoin a blocked
-        #    room after it was purged
-        #
-        #  - user_directory
-        #    This has a room_id column, but it is unused
-        #
-
-        # Other tables that we might want to consider clearing out include:
-        #
-        #  - event_reports
-        #       Given that these are intended for abuse management my initial
-        #       inclination is to leave them in place.
-        #
-        #  - current_state_delta_stream
-        #  - ex_outlier_stream
-        #  - room_tags_revisions
-        #       The problem with these is that they are largeish and there is no room_id
-        #       index on them. In any case we should be clearing out 'stream' tables
-        #       periodically anyway (#5888)
-
-        # TODO: we could probably usefully do a bunch of cache invalidation here
+    def _update_min_depth_for_room_txn(self, txn, room_id, depth):
+        min_depth = self.store._get_min_depth_interaction(txn, room_id)
 
-        logger.info("[purge] done")
-
-        return state_groups
-
-    async def is_event_after(self, event_id1, event_id2):
-        """Returns True if event_id1 is after event_id2 in the stream
-        """
-        to_1, so_1 = await self._get_event_ordering(event_id1)
-        to_2, so_2 = await self._get_event_ordering(event_id2)
-        return (to_1, so_1) > (to_2, so_2)
+        if min_depth is not None and depth >= min_depth:
+            return
 
-    @cachedInlineCallbacks(max_entries=5000)
-    def _get_event_ordering(self, event_id):
-        res = yield self.db.simple_select_one(
-            table="events",
-            retcols=["topological_ordering", "stream_ordering"],
-            keyvalues={"event_id": event_id},
-            allow_none=True,
+        self.db.simple_upsert_txn(
+            txn,
+            table="room_depth",
+            keyvalues={"room_id": room_id},
+            values={"min_depth": depth},
         )
 
-        if not res:
-            raise SynapseError(404, "Could not find event %s" % (event_id,))
-
-        return (int(res["topological_ordering"]), int(res["stream_ordering"]))
-
-    def insert_labels_for_event_txn(
-        self, txn, event_id, labels, room_id, topological_ordering
-    ):
-        """Store the mapping between an event's ID and its labels, with one row per
-        (event_id, label) tuple.
-
-        Args:
-            txn (LoggingTransaction): The transaction to execute.
-            event_id (str): The event's ID.
-            labels (list[str]): A list of text labels.
-            room_id (str): The ID of the room the event was sent to.
-            topological_ordering (int): The position of the event in the room's topology.
+    def _handle_mult_prev_events(self, txn, events):
         """
-        return self.db.simple_insert_many_txn(
-            txn=txn,
-            table="event_labels",
+        For the given event, update the event edges table and forward and
+        backward extremities tables.
+        """
+        self.db.simple_insert_many_txn(
+            txn,
+            table="event_edges",
             values=[
                 {
-                    "event_id": event_id,
-                    "label": label,
-                    "room_id": room_id,
-                    "topological_ordering": topological_ordering,
+                    "event_id": ev.event_id,
+                    "prev_event_id": e_id,
+                    "room_id": ev.room_id,
+                    "is_state": False,
                 }
-                for label in labels
+                for ev in events
+                for e_id in ev.prev_event_ids()
             ],
         )
 
-    def _insert_event_expiry_txn(self, txn, event_id, expiry_ts):
-        """Save the expiry timestamp associated with a given event ID.
-
-        Args:
-            txn (LoggingTransaction): The database transaction to use.
-            event_id (str): The event ID the expiry timestamp is associated with.
-            expiry_ts (int): The timestamp at which to expire (delete) the event.
-        """
-        return self.db.simple_insert_txn(
-            txn=txn,
-            table="event_expiry",
-            values={"event_id": event_id, "expiry_ts": expiry_ts},
-        )
-
-    @defer.inlineCallbacks
-    def expire_event(self, event_id):
-        """Retrieve and expire an event that has expired, and delete its associated
-        expiry timestamp. If the event can't be retrieved, delete its associated
-        timestamp so we don't try to expire it again in the future.
-
-        Args:
-             event_id (str): The ID of the event to delete.
-        """
-        # Try to retrieve the event's content from the database or the event cache.
-        event = yield self.get_event(event_id)
-
-        def delete_expired_event_txn(txn):
-            # Delete the expiry timestamp associated with this event from the database.
-            self._delete_event_expiry_txn(txn, event_id)
-
-            if not event:
-                # If we can't find the event, log a warning and delete the expiry date
-                # from the database so that we don't try to expire it again in the
-                # future.
-                logger.warning(
-                    "Can't expire event %s because we don't have it.", event_id
-                )
-                return
-
-            # Prune the event's dict then convert it to JSON.
-            pruned_json = encode_json(
-                prune_event_dict(event.room_version, event.get_dict())
-            )
-
-            # Update the event_json table to replace the event's JSON with the pruned
-            # JSON.
-            self._censor_event_txn(txn, event.event_id, pruned_json)
-
-            # We need to invalidate the event cache entry for this event because we
-            # changed its content in the database. We can't call
-            # self._invalidate_cache_and_stream because self.get_event_cache isn't of the
-            # right type.
-            txn.call_after(self._get_event_cache.invalidate, (event.event_id,))
-            # Send that invalidation to replication so that other workers also invalidate
-            # the event cache.
-            self._send_invalidation_to_replication(
-                txn, "_get_event_cache", (event.event_id,)
-            )
+        self._update_backward_extremeties(txn, events)
 
-        yield self.db.runInteraction("delete_expired_event", delete_expired_event_txn)
+    def _update_backward_extremeties(self, txn, events):
+        """Updates the event_backward_extremities tables based on the new/updated
+        events being persisted.
 
-    def _delete_event_expiry_txn(self, txn, event_id):
-        """Delete the expiry timestamp associated with an event ID without deleting the
-        actual event.
+        This is called for new events *and* for events that were outliers, but
+        are now being persisted as non-outliers.
 
-        Args:
-            txn (LoggingTransaction): The transaction to use to perform the deletion.
-            event_id (str): The event ID to delete the associated expiry timestamp of.
+        Forward extremities are handled when we first start persisting the events.
         """
-        return self.db.simple_delete_txn(
-            txn=txn, table="event_expiry", keyvalues={"event_id": event_id}
+        events_by_room = {}
+        for ev in events:
+            events_by_room.setdefault(ev.room_id, []).append(ev)
+
+        query = (
+            "INSERT INTO event_backward_extremities (event_id, room_id)"
+            " SELECT ?, ? WHERE NOT EXISTS ("
+            " SELECT 1 FROM event_backward_extremities"
+            " WHERE event_id = ? AND room_id = ?"
+            " )"
+            " AND NOT EXISTS ("
+            " SELECT 1 FROM events WHERE event_id = ? AND room_id = ? "
+            " AND outlier = ?"
+            " )"
         )
 
-    def get_next_event_to_expire(self):
-        """Retrieve the entry with the lowest expiry timestamp in the event_expiry
-        table, or None if there's no more event to expire.
-
-        Returns: Deferred[Optional[Tuple[str, int]]]
-            A tuple containing the event ID as its first element and an expiry timestamp
-            as its second one, if there's at least one row in the event_expiry table.
-            None otherwise.
-        """
-
-        def get_next_event_to_expire_txn(txn):
-            txn.execute(
-                """
-                SELECT event_id, expiry_ts FROM event_expiry
-                ORDER BY expiry_ts ASC LIMIT 1
-                """
-            )
-
-            return txn.fetchone()
-
-        return self.db.runInteraction(
-            desc="get_next_event_to_expire", func=get_next_event_to_expire_txn
+        txn.executemany(
+            query,
+            [
+                (e_id, ev.room_id, e_id, ev.room_id, e_id, ev.room_id, False)
+                for ev in events
+                for e_id in ev.prev_event_ids()
+                if not ev.internal_metadata.is_outlier()
+            ],
         )
 
-
-AllNewEventsResult = namedtuple(
-    "AllNewEventsResult",
-    [
-        "new_forward_events",
-        "new_backfill_events",
-        "forward_ex_outliers",
-        "backward_ex_outliers",
-    ],
-)
+        query = (
+            "DELETE FROM event_backward_extremities"
+            " WHERE event_id = ? AND room_id = ?"
+        )
+        txn.executemany(
+            query,
+            [
+                (ev.event_id, ev.room_id)
+                for ev in events
+                if not ev.internal_metadata.is_outlier()
+            ],
+        )
diff --git a/synapse/storage/data_stores/main/events_worker.py b/synapse/storage/data_stores/main/events_worker.py
index b8c1bbdf99..970c31bd05 100644
--- a/synapse/storage/data_stores/main/events_worker.py
+++ b/synapse/storage/data_stores/main/events_worker.py
@@ -27,7 +27,7 @@ from constantly import NamedConstant, Names
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes
-from synapse.api.errors import NotFoundError
+from synapse.api.errors import NotFoundError, SynapseError
 from synapse.api.room_versions import (
     KNOWN_ROOM_VERSIONS,
     EventFormatVersions,
@@ -40,7 +40,7 @@ from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.storage._base import SQLBaseStore, make_in_list_sql_clause
 from synapse.storage.database import Database
 from synapse.types import get_domain_from_id
-from synapse.util.caches.descriptors import Cache
+from synapse.util.caches.descriptors import Cache, cached, cachedInlineCallbacks
 from synapse.util.iterutils import batch_iter
 from synapse.util.metrics import Measure
 
@@ -1157,4 +1157,152 @@ class EventsWorkerStore(SQLBaseStore):
         rows = await self.db.runInteraction(
             "get_deltas_for_stream_id", get_deltas_for_stream_id_txn, to_token
         )
+
         return rows, to_token, True
+
+    @cached(num_args=5, max_entries=10)
+    def get_all_new_events(
+        self,
+        last_backfill_id,
+        last_forward_id,
+        current_backfill_id,
+        current_forward_id,
+        limit,
+    ):
+        """Get all the new events that have arrived at the server either as
+        new events or as backfilled events"""
+        have_backfill_events = last_backfill_id != current_backfill_id
+        have_forward_events = last_forward_id != current_forward_id
+
+        if not have_backfill_events and not have_forward_events:
+            return defer.succeed(AllNewEventsResult([], [], [], [], []))
+
+        def get_all_new_events_txn(txn):
+            sql = (
+                "SELECT e.stream_ordering, e.event_id, e.room_id, e.type,"
+                " state_key, redacts"
+                " FROM events AS e"
+                " LEFT JOIN redactions USING (event_id)"
+                " LEFT JOIN state_events USING (event_id)"
+                " WHERE ? < stream_ordering AND stream_ordering <= ?"
+                " ORDER BY stream_ordering ASC"
+                " LIMIT ?"
+            )
+            if have_forward_events:
+                txn.execute(sql, (last_forward_id, current_forward_id, limit))
+                new_forward_events = txn.fetchall()
+
+                if len(new_forward_events) == limit:
+                    upper_bound = new_forward_events[-1][0]
+                else:
+                    upper_bound = current_forward_id
+
+                sql = (
+                    "SELECT event_stream_ordering, event_id, state_group"
+                    " FROM ex_outlier_stream"
+                    " WHERE ? > event_stream_ordering"
+                    " AND event_stream_ordering >= ?"
+                    " ORDER BY event_stream_ordering DESC"
+                )
+                txn.execute(sql, (last_forward_id, upper_bound))
+                forward_ex_outliers = txn.fetchall()
+            else:
+                new_forward_events = []
+                forward_ex_outliers = []
+
+            sql = (
+                "SELECT -e.stream_ordering, e.event_id, e.room_id, e.type,"
+                " state_key, redacts"
+                " FROM events AS e"
+                " LEFT JOIN redactions USING (event_id)"
+                " LEFT JOIN state_events USING (event_id)"
+                " WHERE ? > stream_ordering AND stream_ordering >= ?"
+                " ORDER BY stream_ordering DESC"
+                " LIMIT ?"
+            )
+            if have_backfill_events:
+                txn.execute(sql, (-last_backfill_id, -current_backfill_id, limit))
+                new_backfill_events = txn.fetchall()
+
+                if len(new_backfill_events) == limit:
+                    upper_bound = new_backfill_events[-1][0]
+                else:
+                    upper_bound = current_backfill_id
+
+                sql = (
+                    "SELECT -event_stream_ordering, event_id, state_group"
+                    " FROM ex_outlier_stream"
+                    " WHERE ? > event_stream_ordering"
+                    " AND event_stream_ordering >= ?"
+                    " ORDER BY event_stream_ordering DESC"
+                )
+                txn.execute(sql, (-last_backfill_id, -upper_bound))
+                backward_ex_outliers = txn.fetchall()
+            else:
+                new_backfill_events = []
+                backward_ex_outliers = []
+
+            return AllNewEventsResult(
+                new_forward_events,
+                new_backfill_events,
+                forward_ex_outliers,
+                backward_ex_outliers,
+            )
+
+        return self.db.runInteraction("get_all_new_events", get_all_new_events_txn)
+
+    async def is_event_after(self, event_id1, event_id2):
+        """Returns True if event_id1 is after event_id2 in the stream
+        """
+        to_1, so_1 = await self._get_event_ordering(event_id1)
+        to_2, so_2 = await self._get_event_ordering(event_id2)
+        return (to_1, so_1) > (to_2, so_2)
+
+    @cachedInlineCallbacks(max_entries=5000)
+    def _get_event_ordering(self, event_id):
+        res = yield self.db.simple_select_one(
+            table="events",
+            retcols=["topological_ordering", "stream_ordering"],
+            keyvalues={"event_id": event_id},
+            allow_none=True,
+        )
+
+        if not res:
+            raise SynapseError(404, "Could not find event %s" % (event_id,))
+
+        return (int(res["topological_ordering"]), int(res["stream_ordering"]))
+
+    def get_next_event_to_expire(self):
+        """Retrieve the entry with the lowest expiry timestamp in the event_expiry
+        table, or None if there's no more event to expire.
+
+        Returns: Deferred[Optional[Tuple[str, int]]]
+            A tuple containing the event ID as its first element and an expiry timestamp
+            as its second one, if there's at least one row in the event_expiry table.
+            None otherwise.
+        """
+
+        def get_next_event_to_expire_txn(txn):
+            txn.execute(
+                """
+                SELECT event_id, expiry_ts FROM event_expiry
+                ORDER BY expiry_ts ASC LIMIT 1
+                """
+            )
+
+            return txn.fetchone()
+
+        return self.db.runInteraction(
+            desc="get_next_event_to_expire", func=get_next_event_to_expire_txn
+        )
+
+
+AllNewEventsResult = namedtuple(
+    "AllNewEventsResult",
+    [
+        "new_forward_events",
+        "new_backfill_events",
+        "forward_ex_outliers",
+        "backward_ex_outliers",
+    ],
+)
diff --git a/synapse/storage/data_stores/main/metrics.py b/synapse/storage/data_stores/main/metrics.py
new file mode 100644
index 0000000000..dad5bbc602
--- /dev/null
+++ b/synapse/storage/data_stores/main/metrics.py
@@ -0,0 +1,128 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import typing
+from collections import Counter
+
+from twisted.internet import defer
+
+from synapse.metrics import BucketCollector
+from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.storage._base import SQLBaseStore
+from synapse.storage.data_stores.main.event_push_actions import (
+    EventPushActionsWorkerStore,
+)
+from synapse.storage.database import Database
+
+
+class ServerMetricsStore(EventPushActionsWorkerStore, SQLBaseStore):
+    """Functions to pull various metrics from the DB, for e.g. phone home
+    stats and prometheus metrics.
+    """
+
+    def __init__(self, database: Database, db_conn, hs):
+        super().__init__(database, db_conn, hs)
+
+        # Collect metrics on the number of forward extremities that exist.
+        # Counter of number of extremities to count
+        self._current_forward_extremities_amount = (
+            Counter()
+        )  # type: typing.Counter[int]
+
+        BucketCollector(
+            "synapse_forward_extremities",
+            lambda: self._current_forward_extremities_amount,
+            buckets=[1, 2, 3, 5, 7, 10, 15, 20, 50, 100, 200, 500, "+Inf"],
+        )
+
+        # Read the extrems every 60 minutes
+        def read_forward_extremities():
+            # run as a background process to make sure that the database transactions
+            # have a logcontext to report to
+            return run_as_background_process(
+                "read_forward_extremities", self._read_forward_extremities
+            )
+
+        hs.get_clock().looping_call(read_forward_extremities, 60 * 60 * 1000)
+
+    async def _read_forward_extremities(self):
+        def fetch(txn):
+            txn.execute(
+                """
+                select count(*) c from event_forward_extremities
+                group by room_id
+                """
+            )
+            return txn.fetchall()
+
+        res = await self.db.runInteraction("read_forward_extremities", fetch)
+        self._current_forward_extremities_amount = Counter([x[0] for x in res])
+
+    @defer.inlineCallbacks
+    def count_daily_messages(self):
+        """
+        Returns an estimate of the number of messages sent in the last day.
+
+        If it has been significantly less or more than one day since the last
+        call to this function, it will return None.
+        """
+
+        def _count_messages(txn):
+            sql = """
+                SELECT COALESCE(COUNT(*), 0) FROM events
+                WHERE type = 'm.room.message'
+                AND stream_ordering > ?
+            """
+            txn.execute(sql, (self.stream_ordering_day_ago,))
+            (count,) = txn.fetchone()
+            return count
+
+        ret = yield self.db.runInteraction("count_messages", _count_messages)
+        return ret
+
+    @defer.inlineCallbacks
+    def count_daily_sent_messages(self):
+        def _count_messages(txn):
+            # This is good enough as if you have silly characters in your own
+            # hostname then thats your own fault.
+            like_clause = "%:" + self.hs.hostname
+
+            sql = """
+                SELECT COALESCE(COUNT(*), 0) FROM events
+                WHERE type = 'm.room.message'
+                    AND sender LIKE ?
+                AND stream_ordering > ?
+            """
+
+            txn.execute(sql, (like_clause, self.stream_ordering_day_ago))
+            (count,) = txn.fetchone()
+            return count
+
+        ret = yield self.db.runInteraction("count_daily_sent_messages", _count_messages)
+        return ret
+
+    @defer.inlineCallbacks
+    def count_daily_active_rooms(self):
+        def _count(txn):
+            sql = """
+                SELECT COALESCE(COUNT(DISTINCT room_id), 0) FROM events
+                WHERE type = 'm.room.message'
+                AND stream_ordering > ?
+            """
+            txn.execute(sql, (self.stream_ordering_day_ago,))
+            (count,) = txn.fetchone()
+            return count
+
+        ret = yield self.db.runInteraction("count_daily_active_rooms", _count)
+        return ret
diff --git a/synapse/storage/data_stores/main/purge_events.py b/synapse/storage/data_stores/main/purge_events.py
new file mode 100644
index 0000000000..a93e1ef198
--- /dev/null
+++ b/synapse/storage/data_stores/main/purge_events.py
@@ -0,0 +1,399 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+from typing import Any, Tuple
+
+from synapse.api.errors import SynapseError
+from synapse.storage._base import SQLBaseStore
+from synapse.storage.data_stores.main.state import StateGroupWorkerStore
+from synapse.types import RoomStreamToken
+
+logger = logging.getLogger(__name__)
+
+
+class PurgeEventsStore(StateGroupWorkerStore, SQLBaseStore):
+    def purge_history(self, room_id, token, delete_local_events):
+        """Deletes room history before a certain point
+
+        Args:
+            room_id (str):
+
+            token (str): A topological token to delete events before
+
+            delete_local_events (bool):
+                if True, we will delete local events as well as remote ones
+                (instead of just marking them as outliers and deleting their
+                state groups).
+
+        Returns:
+            Deferred[set[int]]: The set of state groups that are referenced by
+            deleted events.
+        """
+
+        return self.db.runInteraction(
+            "purge_history",
+            self._purge_history_txn,
+            room_id,
+            token,
+            delete_local_events,
+        )
+
+    def _purge_history_txn(self, txn, room_id, token_str, delete_local_events):
+        token = RoomStreamToken.parse(token_str)
+
+        # Tables that should be pruned:
+        #     event_auth
+        #     event_backward_extremities
+        #     event_edges
+        #     event_forward_extremities
+        #     event_json
+        #     event_push_actions
+        #     event_reference_hashes
+        #     event_search
+        #     event_to_state_groups
+        #     events
+        #     rejections
+        #     room_depth
+        #     state_groups
+        #     state_groups_state
+
+        # we will build a temporary table listing the events so that we don't
+        # have to keep shovelling the list back and forth across the
+        # connection. Annoyingly the python sqlite driver commits the
+        # transaction on CREATE, so let's do this first.
+        #
+        # furthermore, we might already have the table from a previous (failed)
+        # purge attempt, so let's drop the table first.
+
+        txn.execute("DROP TABLE IF EXISTS events_to_purge")
+
+        txn.execute(
+            "CREATE TEMPORARY TABLE events_to_purge ("
+            "    event_id TEXT NOT NULL,"
+            "    should_delete BOOLEAN NOT NULL"
+            ")"
+        )
+
+        # First ensure that we're not about to delete all the forward extremeties
+        txn.execute(
+            "SELECT e.event_id, e.depth FROM events as e "
+            "INNER JOIN event_forward_extremities as f "
+            "ON e.event_id = f.event_id "
+            "AND e.room_id = f.room_id "
+            "WHERE f.room_id = ?",
+            (room_id,),
+        )
+        rows = txn.fetchall()
+        max_depth = max(row[1] for row in rows)
+
+        if max_depth < token.topological:
+            # We need to ensure we don't delete all the events from the database
+            # otherwise we wouldn't be able to send any events (due to not
+            # having any backwards extremeties)
+            raise SynapseError(
+                400, "topological_ordering is greater than forward extremeties"
+            )
+
+        logger.info("[purge] looking for events to delete")
+
+        should_delete_expr = "state_key IS NULL"
+        should_delete_params = ()  # type: Tuple[Any, ...]
+        if not delete_local_events:
+            should_delete_expr += " AND event_id NOT LIKE ?"
+
+            # We include the parameter twice since we use the expression twice
+            should_delete_params += ("%:" + self.hs.hostname, "%:" + self.hs.hostname)
+
+        should_delete_params += (room_id, token.topological)
+
+        # Note that we insert events that are outliers and aren't going to be
+        # deleted, as nothing will happen to them.
+        txn.execute(
+            "INSERT INTO events_to_purge"
+            " SELECT event_id, %s"
+            " FROM events AS e LEFT JOIN state_events USING (event_id)"
+            " WHERE (NOT outlier OR (%s)) AND e.room_id = ? AND topological_ordering < ?"
+            % (should_delete_expr, should_delete_expr),
+            should_delete_params,
+        )
+
+        # We create the indices *after* insertion as that's a lot faster.
+
+        # create an index on should_delete because later we'll be looking for
+        # the should_delete / shouldn't_delete subsets
+        txn.execute(
+            "CREATE INDEX events_to_purge_should_delete"
+            " ON events_to_purge(should_delete)"
+        )
+
+        # We do joins against events_to_purge for e.g. calculating state
+        # groups to purge, etc., so lets make an index.
+        txn.execute("CREATE INDEX events_to_purge_id ON events_to_purge(event_id)")
+
+        txn.execute("SELECT event_id, should_delete FROM events_to_purge")
+        event_rows = txn.fetchall()
+        logger.info(
+            "[purge] found %i events before cutoff, of which %i can be deleted",
+            len(event_rows),
+            sum(1 for e in event_rows if e[1]),
+        )
+
+        logger.info("[purge] Finding new backward extremities")
+
+        # We calculate the new entries for the backward extremeties by finding
+        # events to be purged that are pointed to by events we're not going to
+        # purge.
+        txn.execute(
+            "SELECT DISTINCT e.event_id FROM events_to_purge AS e"
+            " INNER JOIN event_edges AS ed ON e.event_id = ed.prev_event_id"
+            " LEFT JOIN events_to_purge AS ep2 ON ed.event_id = ep2.event_id"
+            " WHERE ep2.event_id IS NULL"
+        )
+        new_backwards_extrems = txn.fetchall()
+
+        logger.info("[purge] replacing backward extremities: %r", new_backwards_extrems)
+
+        txn.execute(
+            "DELETE FROM event_backward_extremities WHERE room_id = ?", (room_id,)
+        )
+
+        # Update backward extremeties
+        txn.executemany(
+            "INSERT INTO event_backward_extremities (room_id, event_id)"
+            " VALUES (?, ?)",
+            [(room_id, event_id) for event_id, in new_backwards_extrems],
+        )
+
+        logger.info("[purge] finding state groups referenced by deleted events")
+
+        # Get all state groups that are referenced by events that are to be
+        # deleted.
+        txn.execute(
+            """
+            SELECT DISTINCT state_group FROM events_to_purge
+            INNER JOIN event_to_state_groups USING (event_id)
+        """
+        )
+
+        referenced_state_groups = {sg for sg, in txn}
+        logger.info(
+            "[purge] found %i referenced state groups", len(referenced_state_groups)
+        )
+
+        logger.info("[purge] removing events from event_to_state_groups")
+        txn.execute(
+            "DELETE FROM event_to_state_groups "
+            "WHERE event_id IN (SELECT event_id from events_to_purge)"
+        )
+        for event_id, _ in event_rows:
+            txn.call_after(self._get_state_group_for_event.invalidate, (event_id,))
+
+        # Delete all remote non-state events
+        for table in (
+            "events",
+            "event_json",
+            "event_auth",
+            "event_edges",
+            "event_forward_extremities",
+            "event_reference_hashes",
+            "event_search",
+            "rejections",
+        ):
+            logger.info("[purge] removing events from %s", table)
+
+            txn.execute(
+                "DELETE FROM %s WHERE event_id IN ("
+                "    SELECT event_id FROM events_to_purge WHERE should_delete"
+                ")" % (table,)
+            )
+
+        # event_push_actions lacks an index on event_id, and has one on
+        # (room_id, event_id) instead.
+        for table in ("event_push_actions",):
+            logger.info("[purge] removing events from %s", table)
+
+            txn.execute(
+                "DELETE FROM %s WHERE room_id = ? AND event_id IN ("
+                "    SELECT event_id FROM events_to_purge WHERE should_delete"
+                ")" % (table,),
+                (room_id,),
+            )
+
+        # Mark all state and own events as outliers
+        logger.info("[purge] marking remaining events as outliers")
+        txn.execute(
+            "UPDATE events SET outlier = ?"
+            " WHERE event_id IN ("
+            "    SELECT event_id FROM events_to_purge "
+            "    WHERE NOT should_delete"
+            ")",
+            (True,),
+        )
+
+        # synapse tries to take out an exclusive lock on room_depth whenever it
+        # persists events (because upsert), and once we run this update, we
+        # will block that for the rest of our transaction.
+        #
+        # So, let's stick it at the end so that we don't block event
+        # persistence.
+        #
+        # We do this by calculating the minimum depth of the backwards
+        # extremities. However, the events in event_backward_extremities
+        # are ones we don't have yet so we need to look at the events that
+        # point to it via event_edges table.
+        txn.execute(
+            """
+            SELECT COALESCE(MIN(depth), 0)
+            FROM event_backward_extremities AS eb
+            INNER JOIN event_edges AS eg ON eg.prev_event_id = eb.event_id
+            INNER JOIN events AS e ON e.event_id = eg.event_id
+            WHERE eb.room_id = ?
+        """,
+            (room_id,),
+        )
+        (min_depth,) = txn.fetchone()
+
+        logger.info("[purge] updating room_depth to %d", min_depth)
+
+        txn.execute(
+            "UPDATE room_depth SET min_depth = ? WHERE room_id = ?",
+            (min_depth, room_id),
+        )
+
+        # finally, drop the temp table. this will commit the txn in sqlite,
+        # so make sure to keep this actually last.
+        txn.execute("DROP TABLE events_to_purge")
+
+        logger.info("[purge] done")
+
+        return referenced_state_groups
+
+    def purge_room(self, room_id):
+        """Deletes all record of a room
+
+        Args:
+            room_id (str)
+
+        Returns:
+            Deferred[List[int]]: The list of state groups to delete.
+        """
+
+        return self.db.runInteraction("purge_room", self._purge_room_txn, room_id)
+
+    def _purge_room_txn(self, txn, room_id):
+        # First we fetch all the state groups that should be deleted, before
+        # we delete that information.
+        txn.execute(
+            """
+                SELECT DISTINCT state_group FROM events
+                INNER JOIN event_to_state_groups USING(event_id)
+                WHERE events.room_id = ?
+            """,
+            (room_id,),
+        )
+
+        state_groups = [row[0] for row in txn]
+
+        # Now we delete tables which lack an index on room_id but have one on event_id
+        for table in (
+            "event_auth",
+            "event_edges",
+            "event_push_actions_staging",
+            "event_reference_hashes",
+            "event_relations",
+            "event_to_state_groups",
+            "redactions",
+            "rejections",
+            "state_events",
+        ):
+            logger.info("[purge] removing %s from %s", room_id, table)
+
+            txn.execute(
+                """
+                DELETE FROM %s WHERE event_id IN (
+                  SELECT event_id FROM events WHERE room_id=?
+                )
+                """
+                % (table,),
+                (room_id,),
+            )
+
+        # and finally, the tables with an index on room_id (or no useful index)
+        for table in (
+            "current_state_events",
+            "event_backward_extremities",
+            "event_forward_extremities",
+            "event_json",
+            "event_push_actions",
+            "event_search",
+            "events",
+            "group_rooms",
+            "public_room_list_stream",
+            "receipts_graph",
+            "receipts_linearized",
+            "room_aliases",
+            "room_depth",
+            "room_memberships",
+            "room_stats_state",
+            "room_stats_current",
+            "room_stats_historical",
+            "room_stats_earliest_token",
+            "rooms",
+            "stream_ordering_to_exterm",
+            "users_in_public_rooms",
+            "users_who_share_private_rooms",
+            # no useful index, but let's clear them anyway
+            "appservice_room_list",
+            "e2e_room_keys",
+            "event_push_summary",
+            "pusher_throttle",
+            "group_summary_rooms",
+            "local_invites",
+            "room_account_data",
+            "room_tags",
+            "local_current_membership",
+        ):
+            logger.info("[purge] removing %s from %s", room_id, table)
+            txn.execute("DELETE FROM %s WHERE room_id=?" % (table,), (room_id,))
+
+        # Other tables we do NOT need to clear out:
+        #
+        #  - blocked_rooms
+        #    This is important, to make sure that we don't accidentally rejoin a blocked
+        #    room after it was purged
+        #
+        #  - user_directory
+        #    This has a room_id column, but it is unused
+        #
+
+        # Other tables that we might want to consider clearing out include:
+        #
+        #  - event_reports
+        #       Given that these are intended for abuse management my initial
+        #       inclination is to leave them in place.
+        #
+        #  - current_state_delta_stream
+        #  - ex_outlier_stream
+        #  - room_tags_revisions
+        #       The problem with these is that they are largeish and there is no room_id
+        #       index on them. In any case we should be clearing out 'stream' tables
+        #       periodically anyway (#5888)
+
+        # TODO: we could probably usefully do a bunch of cache invalidation here
+
+        logger.info("[purge] done")
+
+        return state_groups
diff --git a/synapse/storage/data_stores/main/rejections.py b/synapse/storage/data_stores/main/rejections.py
index 1c07c7a425..27e5a2084a 100644
--- a/synapse/storage/data_stores/main/rejections.py
+++ b/synapse/storage/data_stores/main/rejections.py
@@ -21,17 +21,6 @@ logger = logging.getLogger(__name__)
 
 
 class RejectionsStore(SQLBaseStore):
-    def _store_rejections_txn(self, txn, event_id, reason):
-        self.db.simple_insert_txn(
-            txn,
-            table="rejections",
-            values={
-                "event_id": event_id,
-                "reason": reason,
-                "last_check": self._clock.time_msec(),
-            },
-        )
-
     def get_rejection_reason(self, event_id):
         return self.db.simple_select_one_onecol(
             table="rejections",
diff --git a/synapse/storage/data_stores/main/relations.py b/synapse/storage/data_stores/main/relations.py
index 046c2b4845..7d477f8d01 100644
--- a/synapse/storage/data_stores/main/relations.py
+++ b/synapse/storage/data_stores/main/relations.py
@@ -324,62 +324,4 @@ class RelationsWorkerStore(SQLBaseStore):
 
 
 class RelationsStore(RelationsWorkerStore):
-    def _handle_event_relations(self, txn, event):
-        """Handles inserting relation data during peristence of events
-
-        Args:
-            txn
-            event (EventBase)
-        """
-        relation = event.content.get("m.relates_to")
-        if not relation:
-            # No relations
-            return
-
-        rel_type = relation.get("rel_type")
-        if rel_type not in (
-            RelationTypes.ANNOTATION,
-            RelationTypes.REFERENCE,
-            RelationTypes.REPLACE,
-        ):
-            # Unknown relation type
-            return
-
-        parent_id = relation.get("event_id")
-        if not parent_id:
-            # Invalid relation
-            return
-
-        aggregation_key = relation.get("key")
-
-        self.db.simple_insert_txn(
-            txn,
-            table="event_relations",
-            values={
-                "event_id": event.event_id,
-                "relates_to_id": parent_id,
-                "relation_type": rel_type,
-                "aggregation_key": aggregation_key,
-            },
-        )
-
-        txn.call_after(self.get_relations_for_event.invalidate_many, (parent_id,))
-        txn.call_after(
-            self.get_aggregation_groups_for_event.invalidate_many, (parent_id,)
-        )
-
-        if rel_type == RelationTypes.REPLACE:
-            txn.call_after(self.get_applicable_edit.invalidate, (parent_id,))
-
-    def _handle_redaction(self, txn, redacted_event_id):
-        """Handles receiving a redaction and checking whether we need to remove
-        any redacted relations from the database.
-
-        Args:
-            txn
-            redacted_event_id (str): The event that was redacted.
-        """
-
-        self.db.simple_delete_txn(
-            txn, table="event_relations", keyvalues={"event_id": redacted_event_id}
-        )
+    pass
diff --git a/synapse/storage/data_stores/main/room.py b/synapse/storage/data_stores/main/room.py
index cafa664c16..46f643c6b9 100644
--- a/synapse/storage/data_stores/main/room.py
+++ b/synapse/storage/data_stores/main/room.py
@@ -21,8 +21,6 @@ from abc import abstractmethod
 from enum import Enum
 from typing import Any, Dict, List, Optional, Tuple
 
-from six import integer_types
-
 from canonicaljson import json
 
 from twisted.internet import defer
@@ -1302,53 +1300,6 @@ class RoomStore(RoomBackgroundUpdateStore, RoomWorkerStore, SearchStore):
 
         return self.db.runInteraction("get_rooms", f)
 
-    def _store_room_topic_txn(self, txn, event):
-        if hasattr(event, "content") and "topic" in event.content:
-            self.store_event_search_txn(
-                txn, event, "content.topic", event.content["topic"]
-            )
-
-    def _store_room_name_txn(self, txn, event):
-        if hasattr(event, "content") and "name" in event.content:
-            self.store_event_search_txn(
-                txn, event, "content.name", event.content["name"]
-            )
-
-    def _store_room_message_txn(self, txn, event):
-        if hasattr(event, "content") and "body" in event.content:
-            self.store_event_search_txn(
-                txn, event, "content.body", event.content["body"]
-            )
-
-    def _store_retention_policy_for_room_txn(self, txn, event):
-        if hasattr(event, "content") and (
-            "min_lifetime" in event.content or "max_lifetime" in event.content
-        ):
-            if (
-                "min_lifetime" in event.content
-                and not isinstance(event.content.get("min_lifetime"), integer_types)
-            ) or (
-                "max_lifetime" in event.content
-                and not isinstance(event.content.get("max_lifetime"), integer_types)
-            ):
-                # Ignore the event if one of the value isn't an integer.
-                return
-
-            self.db.simple_insert_txn(
-                txn=txn,
-                table="room_retention",
-                values={
-                    "room_id": event.room_id,
-                    "event_id": event.event_id,
-                    "min_lifetime": event.content.get("min_lifetime"),
-                    "max_lifetime": event.content.get("max_lifetime"),
-                },
-            )
-
-            self._invalidate_cache_and_stream(
-                txn, self.get_retention_policy_for_room, (event.room_id,)
-            )
-
     def add_event_report(
         self, room_id, event_id, user_id, reason, content, received_ts
     ):
diff --git a/synapse/storage/data_stores/main/roommember.py b/synapse/storage/data_stores/main/roommember.py
index ae9a76713c..04ffdcf934 100644
--- a/synapse/storage/data_stores/main/roommember.py
+++ b/synapse/storage/data_stores/main/roommember.py
@@ -1050,96 +1050,6 @@ class RoomMemberStore(RoomMemberWorkerStore, RoomMemberBackgroundUpdateStore):
     def __init__(self, database: Database, db_conn, hs):
         super(RoomMemberStore, self).__init__(database, db_conn, hs)
 
-    def _store_room_members_txn(self, txn, events, backfilled):
-        """Store a room member in the database.
-        """
-        self.db.simple_insert_many_txn(
-            txn,
-            table="room_memberships",
-            values=[
-                {
-                    "event_id": event.event_id,
-                    "user_id": event.state_key,
-                    "sender": event.user_id,
-                    "room_id": event.room_id,
-                    "membership": event.membership,
-                    "display_name": event.content.get("displayname", None),
-                    "avatar_url": event.content.get("avatar_url", None),
-                }
-                for event in events
-            ],
-        )
-
-        for event in events:
-            txn.call_after(
-                self._membership_stream_cache.entity_has_changed,
-                event.state_key,
-                event.internal_metadata.stream_ordering,
-            )
-            txn.call_after(
-                self.get_invited_rooms_for_local_user.invalidate, (event.state_key,)
-            )
-
-            # We update the local_invites table only if the event is "current",
-            # i.e., its something that has just happened. If the event is an
-            # outlier it is only current if its an "out of band membership",
-            # like a remote invite or a rejection of a remote invite.
-            is_new_state = not backfilled and (
-                not event.internal_metadata.is_outlier()
-                or event.internal_metadata.is_out_of_band_membership()
-            )
-            is_mine = self.hs.is_mine_id(event.state_key)
-            if is_new_state and is_mine:
-                if event.membership == Membership.INVITE:
-                    self.db.simple_insert_txn(
-                        txn,
-                        table="local_invites",
-                        values={
-                            "event_id": event.event_id,
-                            "invitee": event.state_key,
-                            "inviter": event.sender,
-                            "room_id": event.room_id,
-                            "stream_id": event.internal_metadata.stream_ordering,
-                        },
-                    )
-                else:
-                    sql = (
-                        "UPDATE local_invites SET stream_id = ?, replaced_by = ? WHERE"
-                        " room_id = ? AND invitee = ? AND locally_rejected is NULL"
-                        " AND replaced_by is NULL"
-                    )
-
-                    txn.execute(
-                        sql,
-                        (
-                            event.internal_metadata.stream_ordering,
-                            event.event_id,
-                            event.room_id,
-                            event.state_key,
-                        ),
-                    )
-
-                # We also update the `local_current_membership` table with
-                # latest invite info. This will usually get updated by the
-                # `current_state_events` handling, unless its an outlier.
-                if event.internal_metadata.is_outlier():
-                    # This should only happen for out of band memberships, so
-                    # we add a paranoia check.
-                    assert event.internal_metadata.is_out_of_band_membership()
-
-                    self.db.simple_upsert_txn(
-                        txn,
-                        table="local_current_membership",
-                        keyvalues={
-                            "room_id": event.room_id,
-                            "user_id": event.state_key,
-                        },
-                        values={
-                            "event_id": event.event_id,
-                            "membership": event.membership,
-                        },
-                    )
-
     @defer.inlineCallbacks
     def locally_reject_invite(self, user_id, room_id):
         sql = (
diff --git a/synapse/storage/data_stores/main/search.py b/synapse/storage/data_stores/main/search.py
index 47ebb8a214..ee75b92344 100644
--- a/synapse/storage/data_stores/main/search.py
+++ b/synapse/storage/data_stores/main/search.py
@@ -347,29 +347,6 @@ class SearchStore(SearchBackgroundUpdateStore):
     def __init__(self, database: Database, db_conn, hs):
         super(SearchStore, self).__init__(database, db_conn, hs)
 
-    def store_event_search_txn(self, txn, event, key, value):
-        """Add event to the search table
-
-        Args:
-            txn (cursor):
-            event (EventBase):
-            key (str):
-            value (str):
-        """
-        self.store_search_entries_txn(
-            txn,
-            (
-                SearchEntry(
-                    key=key,
-                    value=value,
-                    event_id=event.event_id,
-                    room_id=event.room_id,
-                    stream_ordering=event.internal_metadata.stream_ordering,
-                    origin_server_ts=event.origin_server_ts,
-                ),
-            ),
-        )
-
     @defer.inlineCallbacks
     def search_msgs(self, room_ids, search_term, keys):
         """Performs a full text search over events with given keys.
diff --git a/synapse/storage/data_stores/main/signatures.py b/synapse/storage/data_stores/main/signatures.py
index 563216b63c..36244d9f5d 100644
--- a/synapse/storage/data_stores/main/signatures.py
+++ b/synapse/storage/data_stores/main/signatures.py
@@ -13,23 +13,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import six
-
 from unpaddedbase64 import encode_base64
 
 from twisted.internet import defer
 
-from synapse.crypto.event_signing import compute_event_reference_hash
 from synapse.storage._base import SQLBaseStore
 from synapse.util.caches.descriptors import cached, cachedList
 
-# py2 sqlite has buffer hardcoded as only binary type, so we must use it,
-# despite being deprecated and removed in favor of memoryview
-if six.PY2:
-    db_binary_type = six.moves.builtins.buffer
-else:
-    db_binary_type = memoryview
-
 
 class SignatureWorkerStore(SQLBaseStore):
     @cached()
@@ -79,23 +69,3 @@ class SignatureWorkerStore(SQLBaseStore):
 
 class SignatureStore(SignatureWorkerStore):
     """Persistence for event signatures and hashes"""
-
-    def _store_event_reference_hashes_txn(self, txn, events):
-        """Store a hash for a PDU
-        Args:
-            txn (cursor):
-            events (list): list of Events.
-        """
-
-        vals = []
-        for event in events:
-            ref_alg, ref_hash_bytes = compute_event_reference_hash(event)
-            vals.append(
-                {
-                    "event_id": event.event_id,
-                    "algorithm": ref_alg,
-                    "hash": db_binary_type(ref_hash_bytes),
-                }
-            )
-
-        self.db.simple_insert_many_txn(txn, table="event_reference_hashes", values=vals)
diff --git a/synapse/storage/data_stores/main/state.py b/synapse/storage/data_stores/main/state.py
index 3a3b9a8e72..21052fcc7a 100644
--- a/synapse/storage/data_stores/main/state.py
+++ b/synapse/storage/data_stores/main/state.py
@@ -16,17 +16,12 @@
 import collections.abc
 import logging
 from collections import namedtuple
-from typing import Iterable, Tuple
-
-from six import iteritems
 
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import NotFoundError, UnsupportedRoomVersionError
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
-from synapse.events import EventBase
-from synapse.events.snapshot import EventContext
 from synapse.storage._base import SQLBaseStore
 from synapse.storage.data_stores.main.events_worker import EventsWorkerStore
 from synapse.storage.data_stores.main.roommember import RoomMemberWorkerStore
@@ -473,33 +468,3 @@ class StateStore(StateGroupWorkerStore, MainStateBackgroundUpdateStore):
 
     def __init__(self, database: Database, db_conn, hs):
         super(StateStore, self).__init__(database, db_conn, hs)
-
-    def _store_event_state_mappings_txn(
-        self, txn, events_and_contexts: Iterable[Tuple[EventBase, EventContext]]
-    ):
-        state_groups = {}
-        for event, context in events_and_contexts:
-            if event.internal_metadata.is_outlier():
-                continue
-
-            # if the event was rejected, just give it the same state as its
-            # predecessor.
-            if context.rejected:
-                state_groups[event.event_id] = context.state_group_before_event
-                continue
-
-            state_groups[event.event_id] = context.state_group
-
-        self.db.simple_insert_many_txn(
-            txn,
-            table="event_to_state_groups",
-            values=[
-                {"state_group": state_group_id, "event_id": event_id}
-                for event_id, state_group_id in iteritems(state_groups)
-            ],
-        )
-
-        for event_id, state_group_id in iteritems(state_groups):
-            txn.call_after(
-                self._get_state_group_for_event.prefill, (event_id,), state_group_id
-            )
diff --git a/synapse/storage/persist_events.py b/synapse/storage/persist_events.py
index 0f9ac1cf09..41881ea20b 100644
--- a/synapse/storage/persist_events.py
+++ b/synapse/storage/persist_events.py
@@ -23,7 +23,6 @@ from typing import Iterable, List, Optional, Set, Tuple
 from six import iteritems
 from six.moves import range
 
-import attr
 from prometheus_client import Counter, Histogram
 
 from twisted.internet import defer
@@ -35,6 +34,7 @@ from synapse.logging.context import PreserveLoggingContext, make_deferred_yielda
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.state import StateResolutionStore
 from synapse.storage.data_stores import DataStores
+from synapse.storage.data_stores.main.events import DeltaState
 from synapse.types import StateMap
 from synapse.util.async_helpers import ObservableDeferred
 from synapse.util.metrics import Measure
@@ -73,22 +73,6 @@ stale_forward_extremities_counter = Histogram(
 )
 
 
-@attr.s(slots=True)
-class DeltaState:
-    """Deltas to use to update the `current_state_events` table.
-
-    Attributes:
-        to_delete: List of type/state_keys to delete from current state
-        to_insert: Map of state to upsert into current state
-        no_longer_in_room: The server is not longer in the room, so the room
-            should e.g. be removed from `current_state_events` table.
-    """
-
-    to_delete = attr.ib(type=List[Tuple[str, str]])
-    to_insert = attr.ib(type=StateMap[str])
-    no_longer_in_room = attr.ib(type=bool, default=False)
-
-
 class _EventPeristenceQueue(object):
     """Queues up events so that they can be persisted in bulk with only one
     concurrent transaction per room.
@@ -205,6 +189,7 @@ class EventsPersistenceStorage(object):
         # store for now.
         self.main_store = stores.main
         self.state_store = stores.state
+        self.persist_events_store = stores.persist_events
 
         self._clock = hs.get_clock()
         self.is_mine_id = hs.is_mine_id
@@ -445,7 +430,7 @@ class EventsPersistenceStorage(object):
                         if current_state is not None:
                             current_state_for_room[room_id] = current_state
 
-            await self.main_store._persist_events_and_state_updates(
+            await self.persist_events_store._persist_events_and_state_updates(
                 chunk,
                 current_state_for_room=current_state_for_room,
                 state_delta_for_room=state_delta_for_room,
@@ -491,13 +476,15 @@ class EventsPersistenceStorage(object):
         )
 
         # Remove any events which are prev_events of any existing events.
-        existing_prevs = await self.main_store._get_events_which_are_prevs(result)
+        existing_prevs = await self.persist_events_store._get_events_which_are_prevs(
+            result
+        )
         result.difference_update(existing_prevs)
 
         # Finally handle the case where the new events have soft-failed prev
         # events. If they do we need to remove them and their prev events,
         # otherwise we end up with dangling extremities.
-        existing_prevs = await self.main_store._get_prevs_before_rejected(
+        existing_prevs = await self.persist_events_store._get_prevs_before_rejected(
             e_id for event in new_events for e_id in event.prev_event_ids()
         )
         result.difference_update(existing_prevs)
diff --git a/tests/storage/test_event_push_actions.py b/tests/storage/test_event_push_actions.py
index d4bcf1821e..b45bc9c115 100644
--- a/tests/storage/test_event_push_actions.py
+++ b/tests/storage/test_event_push_actions.py
@@ -35,6 +35,7 @@ class EventPushActionsStoreTestCase(tests.unittest.TestCase):
     def setUp(self):
         hs = yield tests.utils.setup_test_homeserver(self.addCleanup)
         self.store = hs.get_datastore()
+        self.persist_events_store = hs.get_datastores().persist_events
 
     @defer.inlineCallbacks
     def test_get_unread_push_actions_for_user_in_range_for_http(self):
@@ -76,7 +77,7 @@ class EventPushActionsStoreTestCase(tests.unittest.TestCase):
             )
             yield self.store.db.runInteraction(
                 "",
-                self.store._set_push_actions_for_event_and_users_txn,
+                self.persist_events_store._set_push_actions_for_event_and_users_txn,
                 [(event, None)],
                 [(event, None)],
             )