Optimize slot reuse after garbage collection in logicalrep_worker_launch().

Previously, when logicalrep_worker_launch() ran garbage collection and
cleaned up at least one worker slot, it would rescan all worker slots to
find a free one. However, since it is guaranteed that at least one slot was
freed in this case, this additional scan was unnecessary.

This commit removes the redundant scan and makes logicalrep_worker_launch()
immediately reuse the freed slot.

Author: MasaoFujii

src/backend/replication/logical/launcher.c

@@ -365,7 +365,6 @@ logicalrep_worker_launch(LogicalRepWorkerType wtype,
 	 */
 	LWLockAcquire(LogicalRepWorkerLock, LW_EXCLUSIVE);
 
-retry:
 	/* Find unused worker slot. */
 	for (i = 0; i < max_logical_replication_workers; i++)
 	{
@@ -415,11 +414,21 @@ logicalrep_worker_launch(LogicalRepWorkerType wtype,
 
 				logicalrep_worker_cleanup(w);
 				did_cleanup = true;
+
+				if (worker == NULL)
+				{
+					worker = w;
+					slot = i;
+				}
 			}
 		}
 
+		/*
+		 * Count the current number of sync and parallel apply workers again,
+		 * since garbage collection may have changed it.
+		 */
 		if (did_cleanup)
-			goto retry;
+			logicalrep_worker_count(subid, &nsyncworkers, &nparallelapplyworkers);
 	}
 
 	/*