Track unconverted device list outbound pokes using a position instead (#14516)

When a local device list change is added to
`device_lists_changes_in_room`, the `converted_to_destinations` flag is
set to `FALSE` and the `_handle_new_device_update_async` background
process is started. This background process looks for unconverted rows
in `device_lists_changes_in_room`, copies them to
`device_lists_outbound_pokes` and updates the flag.

To update the `converted_to_destinations` flag, the database performs a
`DELETE` and `INSERT` internally, which fragments the table. To avoid
this, track unconverted rows using a `(stream ID, room ID)` position
instead of the flag.

From now on, the `converted_to_destinations` column indicates rows that
need converting to outbound pokes, but does not indicate whether the
conversion has already taken place.

Closes #14037.

Signed-off-by: Sean Quah <seanq@matrix.org>

1 files changed, 7 insertions, 6 deletions

diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index 0dc44b246c..a14b13aec8 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -2075,13 +2075,14 @@ class DatabasePool:
         retcols: Collection[str],
         allow_none: bool = False,
     ) -> Optional[Dict[str, Any]]:
-        select_sql = "SELECT %s FROM %s WHERE %s" % (
-            ", ".join(retcols),
-            table,
-            " AND ".join("%s = ?" % (k,) for k in keyvalues),
-        )
+        select_sql = "SELECT %s FROM %s" % (", ".join(retcols), table)
+
+        if keyvalues:
+            select_sql += " WHERE %s" % (" AND ".join("%s = ?" % k for k in keyvalues),)
+            txn.execute(select_sql, list(keyvalues.values()))
+        else:
+            txn.execute(select_sql)
 
-        txn.execute(select_sql, list(keyvalues.values()))
         row = txn.fetchone()
 
         if not row: