Avoid creating parallel apply state hash table unless required.

Amit Kapila · Amit Kapila · commit dca8b01f5f1f · 2023-01-13T08:28:05.000+05:30
This hash table is used to cache the state of streaming transactions being applied by the parallel apply workers. So, this should be created only when we are successful in launching at least one worker. This avoids rare case memory leak when we are never able to launch any worker. Author: Ted Yu Discussion: https://postgr.es/m/CALte62wg0rBR3Vj2beV=HiWo2qG9L0hzKcX=yULNER0wmf4aEw@mail.gmail.com
diff --git a/src/backend/replication/logical/applyparallelworker.c b/src/backend/replication/logical/applyparallelworker.c
@@ -475,6 +475,10 @@ pa_allocate_worker(TransactionId xid)
 	if (!pa_can_start())
 		return;
 
+	winfo = pa_launch_parallel_worker();
+	if (!winfo)
+		return;
+
 	/* First time through, initialize parallel apply worker state hashtable. */
 	if (!ParallelApplyTxnHash)
 	{
@@ -490,10 +494,6 @@ pa_allocate_worker(TransactionId xid)
 										   HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
 	}
 
-	winfo = pa_launch_parallel_worker();
-	if (!winfo)
-		return;
-
 	/* Create an entry for the requested transaction. */
 	entry = hash_search(ParallelApplyTxnHash, &xid, HASH_ENTER, &found);
 	if (found)
