diff --git a/synapse/storage/search.py b/synapse/storage/search.py
index f1ac9ba0fd..7c80fab277 100644
--- a/synapse/storage/search.py
+++ b/synapse/storage/search.py
@@ -16,6 +16,7 @@
from collections import namedtuple
import logging
import re
+import sys
import ujson as json
from twisted.internet import defer
@@ -289,7 +290,37 @@ class SearchStore(BackgroundUpdateStore):
entry.stream_ordering, entry.origin_server_ts,
) for entry in entries)
- txn.executemany(sql, args)
+ # inserts to a GIN index are normally batched up into a pending
+ # list, and then all committed together once the list gets to a
+ # certain size. The trouble with that is that postgres (pre-9.5)
+ # uses work_mem to determine the length of the list, and work_mem
+ # is typically very large.
+ #
+ # We therefore reduce work_mem while we do the insert.
+ #
+ # (postgres 9.5 uses the separate gin_pending_list_limit setting,
+ # so doesn't suffer the same problem, but changing work_mem will
+ # be harmless)
+
+ txn.execute("SET work_mem='256kB'")
+ try:
+ txn.executemany(sql, args)
+ except Exception:
+ # we need to reset work_mem, but doing so may throw a new
+ # exception and we want to preserve the original
+ t, v, tb = sys.exc_info()
+ try:
+ txn.execute("RESET work_mem")
+ except Exception as e:
+ logger.warn(
+ "exception resetting work_mem during exception "
+ "handling: %r",
+ e,
+ )
+ raise t, v, tb
+ else:
+ txn.execute("RESET work_mem")
+
elif isinstance(self.database_engine, Sqlite3Engine):
sql = (
"INSERT INTO event_search (event_id, room_id, key, value)"
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