Filter out auth chain queries that don't exist (#16552)

matrix-org · Nov 22, 2023 · 460743d · 460743d
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diff --git a/changelog.d/16552.misc b/changelog.d/16552.misc
@@ -0,0 +1 @@
+Reduce a little database load while processing state auth chains.
diff --git a/synapse/storage/databases/main/event_federation.py b/synapse/storage/databases/main/event_federation.py
@@ -301,6 +301,11 @@ def _get_auth_chain_ids_using_cover_index_txn(
         # Add the initial set of chains, excluding the sequence corresponding to
         # initial event.
         for chain_id, seq_no in event_chains.items():
+            # Check if the initial event is the first item in the chain. If so, then
+            # there is nothing new to add from this chain.
+            if seq_no == 1:
+                continue
+
             chains[chain_id] = max(seq_no - 1, chains.get(chain_id, 0))
 
         # Now for each chain we figure out the maximum sequence number reachable