Fix DB query on startup for negative streams. (#8447)

erikjohnston · web-flow · commit 695240d34a9d · 2020-10-02T12:22:19.000+01:00
For negative streams we have to negate the internal stream ID before
querying the DB.

The effect of this bug was to query far too many rows, slowing start up
time, but we would correctly filter the results afterwards so there was
no ill effect.
diff --git a/changelog.d/8447.bugfix b/changelog.d/8447.bugfix
@@ -0,0 +1 @@
+Fix DB query on startup for negative streams which caused long start up times. Introduced in #8374.
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
@@ -341,7 +341,7 @@ def _load_current_ids(
                 "cmp": "<=" if self._positive else ">=",
             }
             sql = self._db.engine.convert_param_style(sql)
-            cur.execute(sql, (min_stream_id,))
+            cur.execute(sql, (min_stream_id * self._return_factor,))
 
             self._persisted_upto_position = min_stream_id
 

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Fix DB query on startup for negative streams which caused long start up times. Introduced in #8374.`
Original file line number	Diff line number	Diff line change
`@@ -341,7 +341,7 @@ def _load_current_ids(`
`341`	`341`	`"cmp": "<=" if self._positive else ">=",`
`342`	`342`	`}`
`343`	`343`	`sql = self._db.engine.convert_param_style(sql)`
`344`		`- cur.execute(sql, (min_stream_id,))`
	`344`	`+ cur.execute(sql, (min_stream_id * self._return_factor,))`
`345`	`345`
`346`	`346`	`self._persisted_upto_position = min_stream_id`
`347`	`347`