diff --git a/synapse/storage/databases/state/bg_updates.py b/synapse/storage/databases/state/bg_updates.py
new file mode 100644
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+++ b/synapse/storage/databases/state/bg_updates.py
@@ -0,0 +1,374 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014-2016 OpenMarket Ltd
+#
+# 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 twisted.internet import defer
+
+from synapse.storage._base import SQLBaseStore
+from synapse.storage.database import DatabasePool
+from synapse.storage.engines import PostgresEngine
+from synapse.storage.state import StateFilter
+
+logger = logging.getLogger(__name__)
+
+
+MAX_STATE_DELTA_HOPS = 100
+
+
+class StateGroupBackgroundUpdateStore(SQLBaseStore):
+ """Defines functions related to state groups needed to run the state backgroud
+ updates.
+ """
+
+ def _count_state_group_hops_txn(self, txn, state_group):
+ """Given a state group, count how many hops there are in the tree.
+
+ This is used to ensure the delta chains don't get too long.
+ """
+ if isinstance(self.database_engine, PostgresEngine):
+ sql = """
+ WITH RECURSIVE state(state_group) AS (
+ VALUES(?::bigint)
+ UNION ALL
+ SELECT prev_state_group FROM state_group_edges e, state s
+ WHERE s.state_group = e.state_group
+ )
+ SELECT count(*) FROM state;
+ """
+
+ txn.execute(sql, (state_group,))
+ row = txn.fetchone()
+ if row and row[0]:
+ return row[0]
+ else:
+ return 0
+ else:
+ # We don't use WITH RECURSIVE on sqlite3 as there are distributions
+ # that ship with an sqlite3 version that doesn't support it (e.g. wheezy)
+ next_group = state_group
+ count = 0
+
+ while next_group:
+ next_group = self.db_pool.simple_select_one_onecol_txn(
+ txn,
+ table="state_group_edges",
+ keyvalues={"state_group": next_group},
+ retcol="prev_state_group",
+ allow_none=True,
+ )
+ if next_group:
+ count += 1
+
+ return count
+
+ def _get_state_groups_from_groups_txn(
+ self, txn, groups, state_filter=StateFilter.all()
+ ):
+ results = {group: {} for group in groups}
+
+ where_clause, where_args = state_filter.make_sql_filter_clause()
+
+ # Unless the filter clause is empty, we're going to append it after an
+ # existing where clause
+ if where_clause:
+ where_clause = " AND (%s)" % (where_clause,)
+
+ if isinstance(self.database_engine, PostgresEngine):
+ # Temporarily disable sequential scans in this transaction. This is
+ # a temporary hack until we can add the right indices in
+ txn.execute("SET LOCAL enable_seqscan=off")
+
+ # The below query walks the state_group tree so that the "state"
+ # table includes all state_groups in the tree. It then joins
+ # against `state_groups_state` to fetch the latest state.
+ # It assumes that previous state groups are always numerically
+ # lesser.
+ # The PARTITION is used to get the event_id in the greatest state
+ # group for the given type, state_key.
+ # This may return multiple rows per (type, state_key), but last_value
+ # should be the same.
+ sql = """
+ WITH RECURSIVE state(state_group) AS (
+ VALUES(?::bigint)
+ UNION ALL
+ SELECT prev_state_group FROM state_group_edges e, state s
+ WHERE s.state_group = e.state_group
+ )
+ SELECT DISTINCT ON (type, state_key)
+ type, state_key, event_id
+ FROM state_groups_state
+ WHERE state_group IN (
+ SELECT state_group FROM state
+ ) %s
+ ORDER BY type, state_key, state_group DESC
+ """
+
+ for group in groups:
+ args = [group]
+ args.extend(where_args)
+
+ txn.execute(sql % (where_clause,), args)
+ for row in txn:
+ typ, state_key, event_id = row
+ key = (typ, state_key)
+ results[group][key] = event_id
+ else:
+ max_entries_returned = state_filter.max_entries_returned()
+
+ # We don't use WITH RECURSIVE on sqlite3 as there are distributions
+ # that ship with an sqlite3 version that doesn't support it (e.g. wheezy)
+ for group in groups:
+ next_group = group
+
+ while next_group:
+ # We did this before by getting the list of group ids, and
+ # then passing that list to sqlite to get latest event for
+ # each (type, state_key). However, that was terribly slow
+ # without the right indices (which we can't add until
+ # after we finish deduping state, which requires this func)
+ args = [next_group]
+ args.extend(where_args)
+
+ txn.execute(
+ "SELECT type, state_key, event_id FROM state_groups_state"
+ " WHERE state_group = ? " + where_clause,
+ args,
+ )
+ results[group].update(
+ ((typ, state_key), event_id)
+ for typ, state_key, event_id in txn
+ if (typ, state_key) not in results[group]
+ )
+
+ # If the number of entries in the (type,state_key)->event_id dict
+ # matches the number of (type,state_keys) types we were searching
+ # for, then we must have found them all, so no need to go walk
+ # further down the tree... UNLESS our types filter contained
+ # wildcards (i.e. Nones) in which case we have to do an exhaustive
+ # search
+ if (
+ max_entries_returned is not None
+ and len(results[group]) == max_entries_returned
+ ):
+ break
+
+ next_group = self.db_pool.simple_select_one_onecol_txn(
+ txn,
+ table="state_group_edges",
+ keyvalues={"state_group": next_group},
+ retcol="prev_state_group",
+ allow_none=True,
+ )
+
+ return results
+
+
+class StateBackgroundUpdateStore(StateGroupBackgroundUpdateStore):
+
+ STATE_GROUP_DEDUPLICATION_UPDATE_NAME = "state_group_state_deduplication"
+ STATE_GROUP_INDEX_UPDATE_NAME = "state_group_state_type_index"
+ STATE_GROUPS_ROOM_INDEX_UPDATE_NAME = "state_groups_room_id_idx"
+
+ def __init__(self, database: DatabasePool, db_conn, hs):
+ super(StateBackgroundUpdateStore, self).__init__(database, db_conn, hs)
+ self.db_pool.updates.register_background_update_handler(
+ self.STATE_GROUP_DEDUPLICATION_UPDATE_NAME,
+ self._background_deduplicate_state,
+ )
+ self.db_pool.updates.register_background_update_handler(
+ self.STATE_GROUP_INDEX_UPDATE_NAME, self._background_index_state
+ )
+ self.db_pool.updates.register_background_index_update(
+ self.STATE_GROUPS_ROOM_INDEX_UPDATE_NAME,
+ index_name="state_groups_room_id_idx",
+ table="state_groups",
+ columns=["room_id"],
+ )
+
+ @defer.inlineCallbacks
+ def _background_deduplicate_state(self, progress, batch_size):
+ """This background update will slowly deduplicate state by reencoding
+ them as deltas.
+ """
+ last_state_group = progress.get("last_state_group", 0)
+ rows_inserted = progress.get("rows_inserted", 0)
+ max_group = progress.get("max_group", None)
+
+ BATCH_SIZE_SCALE_FACTOR = 100
+
+ batch_size = max(1, int(batch_size / BATCH_SIZE_SCALE_FACTOR))
+
+ if max_group is None:
+ rows = yield self.db_pool.execute(
+ "_background_deduplicate_state",
+ None,
+ "SELECT coalesce(max(id), 0) FROM state_groups",
+ )
+ max_group = rows[0][0]
+
+ def reindex_txn(txn):
+ new_last_state_group = last_state_group
+ for count in range(batch_size):
+ txn.execute(
+ "SELECT id, room_id FROM state_groups"
+ " WHERE ? < id AND id <= ?"
+ " ORDER BY id ASC"
+ " LIMIT 1",
+ (new_last_state_group, max_group),
+ )
+ row = txn.fetchone()
+ if row:
+ state_group, room_id = row
+
+ if not row or not state_group:
+ return True, count
+
+ txn.execute(
+ "SELECT state_group FROM state_group_edges"
+ " WHERE state_group = ?",
+ (state_group,),
+ )
+
+ # If we reach a point where we've already started inserting
+ # edges we should stop.
+ if txn.fetchall():
+ return True, count
+
+ txn.execute(
+ "SELECT coalesce(max(id), 0) FROM state_groups"
+ " WHERE id < ? AND room_id = ?",
+ (state_group, room_id),
+ )
+ (prev_group,) = txn.fetchone()
+ new_last_state_group = state_group
+
+ if prev_group:
+ potential_hops = self._count_state_group_hops_txn(txn, prev_group)
+ if potential_hops >= MAX_STATE_DELTA_HOPS:
+ # We want to ensure chains are at most this long,#
+ # otherwise read performance degrades.
+ continue
+
+ prev_state = self._get_state_groups_from_groups_txn(
+ txn, [prev_group]
+ )
+ prev_state = prev_state[prev_group]
+
+ curr_state = self._get_state_groups_from_groups_txn(
+ txn, [state_group]
+ )
+ curr_state = curr_state[state_group]
+
+ if not set(prev_state.keys()) - set(curr_state.keys()):
+ # We can only do a delta if the current has a strict super set
+ # of keys
+
+ delta_state = {
+ key: value
+ for key, value in curr_state.items()
+ if prev_state.get(key, None) != value
+ }
+
+ self.db_pool.simple_delete_txn(
+ txn,
+ table="state_group_edges",
+ keyvalues={"state_group": state_group},
+ )
+
+ self.db_pool.simple_insert_txn(
+ txn,
+ table="state_group_edges",
+ values={
+ "state_group": state_group,
+ "prev_state_group": prev_group,
+ },
+ )
+
+ self.db_pool.simple_delete_txn(
+ txn,
+ table="state_groups_state",
+ keyvalues={"state_group": state_group},
+ )
+
+ self.db_pool.simple_insert_many_txn(
+ txn,
+ table="state_groups_state",
+ values=[
+ {
+ "state_group": state_group,
+ "room_id": room_id,
+ "type": key[0],
+ "state_key": key[1],
+ "event_id": state_id,
+ }
+ for key, state_id in delta_state.items()
+ ],
+ )
+
+ progress = {
+ "last_state_group": state_group,
+ "rows_inserted": rows_inserted + batch_size,
+ "max_group": max_group,
+ }
+
+ self.db_pool.updates._background_update_progress_txn(
+ txn, self.STATE_GROUP_DEDUPLICATION_UPDATE_NAME, progress
+ )
+
+ return False, batch_size
+
+ finished, result = yield self.db_pool.runInteraction(
+ self.STATE_GROUP_DEDUPLICATION_UPDATE_NAME, reindex_txn
+ )
+
+ if finished:
+ yield self.db_pool.updates._end_background_update(
+ self.STATE_GROUP_DEDUPLICATION_UPDATE_NAME
+ )
+
+ return result * BATCH_SIZE_SCALE_FACTOR
+
+ @defer.inlineCallbacks
+ def _background_index_state(self, progress, batch_size):
+ def reindex_txn(conn):
+ conn.rollback()
+ if isinstance(self.database_engine, PostgresEngine):
+ # postgres insists on autocommit for the index
+ conn.set_session(autocommit=True)
+ try:
+ txn = conn.cursor()
+ txn.execute(
+ "CREATE INDEX CONCURRENTLY state_groups_state_type_idx"
+ " ON state_groups_state(state_group, type, state_key)"
+ )
+ txn.execute("DROP INDEX IF EXISTS state_groups_state_id")
+ finally:
+ conn.set_session(autocommit=False)
+ else:
+ txn = conn.cursor()
+ txn.execute(
+ "CREATE INDEX state_groups_state_type_idx"
+ " ON state_groups_state(state_group, type, state_key)"
+ )
+ txn.execute("DROP INDEX IF EXISTS state_groups_state_id")
+
+ yield self.db_pool.runWithConnection(reindex_txn)
+
+ yield self.db_pool.updates._end_background_update(
+ self.STATE_GROUP_INDEX_UPDATE_NAME
+ )
+
+ return 1
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