ANALYZE new stream ordering column

changelog.d/10326.bugfix

@@ -0,0 +1 @@
+Fix a long-standing bug where Synapse would return errors after 2<sup>31</sup> events were handled by the server.

synapse/storage/databases/main/events_bg_updates.py

@@ -1141,11 +1141,20 @@ async def _background_replace_stream_ordering_column(
     ) -> int:
         """Drop the old 'stream_ordering' column and rename 'stream_ordering2' into its place."""
 
+        def analyze_new_column(txn: Cursor) -> None:
+            txn.execute("ANALYZE events(stream_ordering2)")
+
         def process(txn: Cursor) -> None:
             for sql in _REPLACE_STREAM_ORDERING_SQL_COMMANDS:
                 logger.info("completing stream_ordering migration: %s", sql)
                 txn.execute(sql)
 
+        # ANALYZE the new column to build stats on it, to encourage PostgreSQL to use the
+        # indexes on it.
+        await self.db_pool.runInteraction(
+            "_background_analyze_new_stream_ordering_column", analyze_new_column
+        )
+
         await self.db_pool.runInteraction(
             "_background_replace_stream_ordering_column", process
         )