Remove Postgres 9.4 support (#5448)

synapse/storage/search.py

@@ -341,29 +341,7 @@ class SearchStore(BackgroundUpdateStore):
                 for entry in entries
             )
 
-            # 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)
-            #
-            # Note that we don't need to worry about restoring it on
-            # exception, because exceptions will cause the transaction to be
-            # rolled back, including the effects of the SET command.
-            #
-            # Also: we use SET rather than SET LOCAL because there's lots of
-            # other stuff going on in this transaction, which want to have the
-            # normal work_mem setting.
-
-            txn.execute("SET work_mem='256kB'")
             txn.executemany(sql, args)
-            txn.execute("RESET work_mem")
 
         elif isinstance(self.database_engine, Sqlite3Engine):
             sql = (