Reintroduce #14376, with bugfix for monoliths (#14468)

* Add tests for StreamIdGenerator

* Drive-by: annotate all defs

* Revert "Revert "Remove slaved id tracker (#14376)" (#14463)"

This reverts commit d63814fd736fed5d3d45ff3af5e6d3bfae50c439, which in
turn reverted 36097e88c4da51fce6556a58c49bd675f4cf20ab. This restores
the latter.

* Fix StreamIdGenerator not handling unpersisted IDs

Spotted by @erikjohnston.

Closes #14456.

* Changelog

Co-authored-by: Nick Mills-Barrett <nick@fizzadar.com>
Co-authored-by: Erik Johnston <erik@matrix.org>

7 files changed, 73 insertions, 100 deletions

diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index c38b8a9e5a..282687ebce 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -27,7 +27,6 @@ from typing import (
 )
 
 from synapse.api.constants import AccountDataTypes
-from synapse.replication.slave.storage._slaved_id_tracker import SlavedIdTracker
 from synapse.replication.tcp.streams import AccountDataStream, TagAccountDataStream
 from synapse.storage._base import db_to_json
 from synapse.storage.database import (
@@ -68,12 +67,11 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
         # to write account data. A value of `True` implies that `_account_data_id_gen`
         # is an `AbstractStreamIdGenerator` and not just a tracker.
         self._account_data_id_gen: AbstractStreamIdTracker
+        self._can_write_to_account_data = (
+            self._instance_name in hs.config.worker.writers.account_data
+        )
 
         if isinstance(database.engine, PostgresEngine):
-            self._can_write_to_account_data = (
-                self._instance_name in hs.config.worker.writers.account_data
-            )
-
             self._account_data_id_gen = MultiWriterIdGenerator(
                 db_conn=db_conn,
                 db=database,
@@ -95,21 +93,13 @@ class AccountDataWorkerStore(PushRulesWorkerStore, CacheInvalidationWorkerStore)
             # `StreamIdGenerator`, otherwise we use `SlavedIdTracker` which gets
             # updated over replication. (Multiple writers are not supported for
             # SQLite).
-            if self._instance_name in hs.config.worker.writers.account_data:
-                self._can_write_to_account_data = True
-                self._account_data_id_gen = StreamIdGenerator(
-                    db_conn,
-                    "room_account_data",
-                    "stream_id",
-                    extra_tables=[("room_tags_revisions", "stream_id")],
-                )
-            else:
-                self._account_data_id_gen = SlavedIdTracker(
-                    db_conn,
-                    "room_account_data",
-                    "stream_id",
-                    extra_tables=[("room_tags_revisions", "stream_id")],
-                )
+            self._account_data_id_gen = StreamIdGenerator(
+                db_conn,
+                "room_account_data",
+                "stream_id",
+                extra_tables=[("room_tags_revisions", "stream_id")],
+                is_writer=self._instance_name in hs.config.worker.writers.account_data,
+            )
 
         account_max = self.get_max_account_data_stream_id()
         self._account_data_stream_cache = StreamChangeCache(
diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index e114c733d1..57230df5ae 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -38,7 +38,6 @@ from synapse.logging.opentracing import (
     whitelisted_homeserver,
 )
 from synapse.metrics.background_process_metrics import wrap_as_background_process
-from synapse.replication.slave.storage._slaved_id_tracker import SlavedIdTracker
 from synapse.replication.tcp.streams._base import DeviceListsStream, UserSignatureStream
 from synapse.storage._base import SQLBaseStore, db_to_json, make_in_list_sql_clause
 from synapse.storage.database import (
@@ -86,28 +85,19 @@ class DeviceWorkerStore(RoomMemberWorkerStore, EndToEndKeyWorkerStore):
     ):
         super().__init__(database, db_conn, hs)
 
-        if hs.config.worker.worker_app is None:
-            self._device_list_id_gen: AbstractStreamIdTracker = StreamIdGenerator(
-                db_conn,
-                "device_lists_stream",
-                "stream_id",
-                extra_tables=[
-                    ("user_signature_stream", "stream_id"),
-                    ("device_lists_outbound_pokes", "stream_id"),
-                    ("device_lists_changes_in_room", "stream_id"),
-                ],
-            )
-        else:
-            self._device_list_id_gen = SlavedIdTracker(
-                db_conn,
-                "device_lists_stream",
-                "stream_id",
-                extra_tables=[
-                    ("user_signature_stream", "stream_id"),
-                    ("device_lists_outbound_pokes", "stream_id"),
-                    ("device_lists_changes_in_room", "stream_id"),
-                ],
-            )
+        # In the worker store this is an ID tracker which we overwrite in the non-worker
+        # class below that is used on the main process.
+        self._device_list_id_gen: AbstractStreamIdTracker = StreamIdGenerator(
+            db_conn,
+            "device_lists_stream",
+            "stream_id",
+            extra_tables=[
+                ("user_signature_stream", "stream_id"),
+                ("device_lists_outbound_pokes", "stream_id"),
+                ("device_lists_changes_in_room", "stream_id"),
+            ],
+            is_writer=hs.config.worker.worker_app is None,
+        )
 
         # Type-ignore: _device_list_id_gen is mixed in from either DataStore (as a
         # StreamIdGenerator) or SlavedDataStore (as a SlavedIdTracker).
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index 8a104f7e93..01e935edef 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -59,7 +59,6 @@ from synapse.metrics.background_process_metrics import (
     run_as_background_process,
     wrap_as_background_process,
 )
-from synapse.replication.slave.storage._slaved_id_tracker import SlavedIdTracker
 from synapse.replication.tcp.streams import BackfillStream
 from synapse.replication.tcp.streams.events import EventsStream
 from synapse.storage._base import SQLBaseStore, db_to_json, make_in_list_sql_clause
@@ -213,26 +212,20 @@ class EventsWorkerStore(SQLBaseStore):
             # `StreamIdGenerator`, otherwise we use `SlavedIdTracker` which gets
             # updated over replication. (Multiple writers are not supported for
             # SQLite).
-            if hs.get_instance_name() in hs.config.worker.writers.events:
-                self._stream_id_gen = StreamIdGenerator(
-                    db_conn,
-                    "events",
-                    "stream_ordering",
-                )
-                self._backfill_id_gen = StreamIdGenerator(
-                    db_conn,
-                    "events",
-                    "stream_ordering",
-                    step=-1,
-                    extra_tables=[("ex_outlier_stream", "event_stream_ordering")],
-                )
-            else:
-                self._stream_id_gen = SlavedIdTracker(
-                    db_conn, "events", "stream_ordering"
-                )
-                self._backfill_id_gen = SlavedIdTracker(
-                    db_conn, "events", "stream_ordering", step=-1
-                )
+            self._stream_id_gen = StreamIdGenerator(
+                db_conn,
+                "events",
+                "stream_ordering",
+                is_writer=hs.get_instance_name() in hs.config.worker.writers.events,
+            )
+            self._backfill_id_gen = StreamIdGenerator(
+                db_conn,
+                "events",
+                "stream_ordering",
+                step=-1,
+                extra_tables=[("ex_outlier_stream", "event_stream_ordering")],
+                is_writer=hs.get_instance_name() in hs.config.worker.writers.events,
+            )
 
         events_max = self._stream_id_gen.get_current_token()
         curr_state_delta_prefill, min_curr_state_delta_id = self.db_pool.get_cache_dict(
diff --git a/synapse/storage/databases/main/push_rule.py b/synapse/storage/databases/main/push_rule.py
index 8ae10f6127..12ad44dbb3 100644
--- a/synapse/storage/databases/main/push_rule.py
+++ b/synapse/storage/databases/main/push_rule.py
@@ -30,7 +30,6 @@ from typing import (
 
 from synapse.api.errors import StoreError
 from synapse.config.homeserver import ExperimentalConfig
-from synapse.replication.slave.storage._slaved_id_tracker import SlavedIdTracker
 from synapse.replication.tcp.streams import PushRulesStream
 from synapse.storage._base import SQLBaseStore
 from synapse.storage.database import (
@@ -111,14 +110,14 @@ class PushRulesWorkerStore(
     ):
         super().__init__(database, db_conn, hs)
 
-        if hs.config.worker.worker_app is None:
-            self._push_rules_stream_id_gen: AbstractStreamIdTracker = StreamIdGenerator(
-                db_conn, "push_rules_stream", "stream_id"
-            )
-        else:
-            self._push_rules_stream_id_gen = SlavedIdTracker(
-                db_conn, "push_rules_stream", "stream_id"
-            )
+        # In the worker store this is an ID tracker which we overwrite in the non-worker
+        # class below that is used on the main process.
+        self._push_rules_stream_id_gen: AbstractStreamIdTracker = StreamIdGenerator(
+            db_conn,
+            "push_rules_stream",
+            "stream_id",
+            is_writer=hs.config.worker.worker_app is None,
+        )
 
         push_rules_prefill, push_rules_id = self.db_pool.get_cache_dict(
             db_conn,
diff --git a/synapse/storage/databases/main/pusher.py b/synapse/storage/databases/main/pusher.py
index 4a01562d45..fee37b9ce4 100644
--- a/synapse/storage/databases/main/pusher.py
+++ b/synapse/storage/databases/main/pusher.py
@@ -27,7 +27,6 @@ from typing import (
 )
 
 from synapse.push import PusherConfig, ThrottleParams
-from synapse.replication.slave.storage._slaved_id_tracker import SlavedIdTracker
 from synapse.replication.tcp.streams import PushersStream
 from synapse.storage._base import SQLBaseStore, db_to_json
 from synapse.storage.database import (
@@ -59,20 +58,15 @@ class PusherWorkerStore(SQLBaseStore):
     ):
         super().__init__(database, db_conn, hs)
 
-        if hs.config.worker.worker_app is None:
-            self._pushers_id_gen: AbstractStreamIdTracker = StreamIdGenerator(
-                db_conn,
-                "pushers",
-                "id",
-                extra_tables=[("deleted_pushers", "stream_id")],
-            )
-        else:
-            self._pushers_id_gen = SlavedIdTracker(
-                db_conn,
-                "pushers",
-                "id",
-                extra_tables=[("deleted_pushers", "stream_id")],
-            )
+        # In the worker store this is an ID tracker which we overwrite in the non-worker
+        # class below that is used on the main process.
+        self._pushers_id_gen: AbstractStreamIdTracker = StreamIdGenerator(
+            db_conn,
+            "pushers",
+            "id",
+            extra_tables=[("deleted_pushers", "stream_id")],
+            is_writer=hs.config.worker.worker_app is None,
+        )
 
         self.db_pool.updates.register_background_update_handler(
             "remove_deactivated_pushers",
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index fbf27497ec..a580e4bdda 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -27,7 +27,6 @@ from typing import (
 )
 
 from synapse.api.constants import EduTypes
-from synapse.replication.slave.storage._slaved_id_tracker import SlavedIdTracker
 from synapse.replication.tcp.streams import ReceiptsStream
 from synapse.storage._base import SQLBaseStore, db_to_json, make_in_list_sql_clause
 from synapse.storage.database import (
@@ -61,6 +60,9 @@ class ReceiptsWorkerStore(SQLBaseStore):
         hs: "HomeServer",
     ):
         self._instance_name = hs.get_instance_name()
+
+        # In the worker store this is an ID tracker which we overwrite in the non-worker
+        # class below that is used on the main process.
         self._receipts_id_gen: AbstractStreamIdTracker
 
         if isinstance(database.engine, PostgresEngine):
@@ -87,14 +89,12 @@ class ReceiptsWorkerStore(SQLBaseStore):
             # `StreamIdGenerator`, otherwise we use `SlavedIdTracker` which gets
             # updated over replication. (Multiple writers are not supported for
             # SQLite).
-            if hs.get_instance_name() in hs.config.worker.writers.receipts:
-                self._receipts_id_gen = StreamIdGenerator(
-                    db_conn, "receipts_linearized", "stream_id"
-                )
-            else:
-                self._receipts_id_gen = SlavedIdTracker(
-                    db_conn, "receipts_linearized", "stream_id"
-                )
+            self._receipts_id_gen = StreamIdGenerator(
+                db_conn,
+                "receipts_linearized",
+                "stream_id",
+                is_writer=hs.get_instance_name() in hs.config.worker.writers.receipts,
+            )
 
         super().__init__(database, db_conn, hs)
 
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
index 2dfe4c0b66..0d7108f01b 100644
--- a/synapse/storage/util/id_generators.py
+++ b/synapse/storage/util/id_generators.py
@@ -186,11 +186,13 @@ class StreamIdGenerator(AbstractStreamIdGenerator):
         column: str,
         extra_tables: Iterable[Tuple[str, str]] = (),
         step: int = 1,
+        is_writer: bool = True,
     ) -> None:
         assert step != 0
         self._lock = threading.Lock()
         self._step: int = step
         self._current: int = _load_current_id(db_conn, table, column, step)
+        self._is_writer = is_writer
         for table, column in extra_tables:
             self._current = (max if step > 0 else min)(
                 self._current, _load_current_id(db_conn, table, column, step)
@@ -204,9 +206,11 @@ class StreamIdGenerator(AbstractStreamIdGenerator):
         self._unfinished_ids: OrderedDict[int, int] = OrderedDict()
 
     def advance(self, instance_name: str, new_id: int) -> None:
-        # `StreamIdGenerator` should only be used when there is a single writer,
-        # so replication should never happen.
-        raise Exception("Replication is not supported by StreamIdGenerator")
+        # Advance should never be called on a writer instance, only over replication
+        if self._is_writer:
+            raise Exception("Replication is not supported by writer StreamIdGenerator")
+
+        self._current = (max if self._step > 0 else min)(self._current, new_id)
 
     def get_next(self) -> AsyncContextManager[int]:
         with self._lock:
@@ -249,6 +253,9 @@ class StreamIdGenerator(AbstractStreamIdGenerator):
         return _AsyncCtxManagerWrapper(manager())
 
     def get_current_token(self) -> int:
+        if not self._is_writer:
+            return self._current
+
         with self._lock:
             if self._unfinished_ids:
                 return next(iter(self._unfinished_ids)) - self._step