Increase batching when fetching auth chains (#16893)

This basically reverts a change that was in
https://github.com/element-hq/synapse/pull/16833, where we reduced the
batching.

The smaller batching can cause performance issues on busy servers and
databases.

2 files changed, 3 insertions, 2 deletions

diff --git a/changelog.d/16893.bugfix b/changelog.d/16893.bugfix
new file mode 100644

index 0000000000..7222cd765c
--- /dev/null
+++ b/changelog.d/16893.bugfix
@@ -0,0 +1 @@
+Fix performance regression when fetching auth chains from the DB. Introduced in v1.100.0.
diff --git a/synapse/storage/databases/main/event_federation.py b/synapse/storage/databases/main/event_federation.py

index 12e882062a..846c3f363a 100644
--- a/synapse/storage/databases/main/event_federation.py
+++ b/synapse/storage/databases/main/event_federation.py
@@ -310,7 +310,7 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
         # Add all linked chains reachable from initial set of chains.
         chains_to_fetch = set(event_chains.keys())
         while chains_to_fetch:
-            batch2 = tuple(itertools.islice(chains_to_fetch, 100))
+            batch2 = tuple(itertools.islice(chains_to_fetch, 1000))
             chains_to_fetch.difference_update(batch2)
             clause, args = make_in_list_sql_clause(
                 txn.database_engine, "origin_chain_id", batch2
@@ -593,7 +593,7 @@ class EventFederationWorkerStore(SignatureWorkerStore, EventsWorkerStore, SQLBas
         # the loop)
         chains_to_fetch = set(seen_chains)
         while chains_to_fetch:
-            batch2 = tuple(itertools.islice(chains_to_fetch, 100))
+            batch2 = tuple(itertools.islice(chains_to_fetch, 1000))
             clause, args = make_in_list_sql_clause(
                 txn.database_engine, "origin_chain_id", batch2
             )