Split up txn for fetching device keys (#15215)

We look up keys in batches, but we should do that outside of the
transaction to avoid starving the database pool.

1 files changed, 9 insertions, 1 deletions

diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index feaa6cdd07..5efe31aa19 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -672,7 +672,15 @@ class DatabasePool:
             f = cast(types.FunctionType, func)  # type: ignore[redundant-cast]
             if f.__closure__:
                 for i, cell in enumerate(f.__closure__):
-                    if inspect.isgenerator(cell.cell_contents):
+                    try:
+                        contents = cell.cell_contents
+                    except ValueError:
+                        # cell.cell_contents can raise if the "cell" is empty,
+                        # which indicates that the variable is currently
+                        # unbound.
+                        continue
+
+                    if inspect.isgenerator(contents):
                         logger.error(
                             "Programming error: function %s references generator %s "
                             "via its closure",