0001_masahiko.patch

diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 6a3a00585f9..cb42d4e572f 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/src/backend/commands/vacuumparallel.c
@@ -656,7 +656,7 @@ parallel_vacuum_process_all_indexes(ParallelVacuumState *pvs, int num_index_scan
 	nworkers = Min(nworkers, pvs->pcxt->nworkers);
 
 	/*
-	 * Reserve workers in autovacuum global state. Note, that we may be given
+	 * Reserve workers in autovacuum global state. Note that we may be given
 	 * fewer workers than we requested.
 	 */
 	if (AmAutoVacuumWorkerProcess() && nworkers > 0)
@@ -706,15 +706,12 @@ parallel_vacuum_process_all_indexes(ParallelVacuumState *pvs, int num_index_scan
 
 		LaunchParallelWorkers(pvs->pcxt);
 
-		if (AmAutoVacuumWorkerProcess() &&
-			pvs->pcxt->nworkers_launched < nworkers)
-		{
-			/*
-			 * Tell autovacuum that we could not launch all the previously
-			 * reserved workers.
-			 */
+		/*
+		 * Tell autovacuum that we could not launch all the previously
+		 * reserved workers.
+		 */
+		if (AmAutoVacuumWorkerProcess() && pvs->pcxt->nworkers_launched < nworkers)
 			AutoVacuumReleaseParallelWorkers(nworkers - pvs->pcxt->nworkers_launched);
-		}
 
 		if (pvs->pcxt->nworkers_launched > 0)
 		{
@@ -765,7 +762,7 @@ parallel_vacuum_process_all_indexes(ParallelVacuumState *pvs, int num_index_scan
 		for (int i = 0; i < pvs->pcxt->nworkers_launched; i++)
 			InstrAccumParallelQuery(&pvs->buffer_usage[i], &pvs->wal_usage[i]);
 
-		/* Also release all previously reserved parallel autovacuum workers */
+		/* Release all the reserved parallel workers for autovacuum */
 		if (AmAutoVacuumWorkerProcess() && pvs->pcxt->nworkers_launched > 0)
 			AutoVacuumReleaseParallelWorkers(pvs->pcxt->nworkers_launched);
 	}
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index bc11970bfee..6ccc88c4e1e 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -152,8 +152,9 @@ static double av_storage_param_cost_delay = -1;
 static int	av_storage_param_cost_limit = -1;
 
 /*
- * Variable to keep number of currently reserved parallel autovacuum workers.
- * It is only relevant for parallel autovacuum leader process.
+ * Tracks the number of parallel workers currently reserved by the
+ * autovacuum worker. This is non-zero only for the parallel autovacuum
+ * leader process.
  */
 static int	av_nworkers_reserved = 0;
 
@@ -3407,33 +3408,24 @@ AutoVacuumRequestWork(AutoVacuumWorkItemType type, Oid relationId,
 }
 
 /*
- * In order to meet the 'autovacuum_max_parallel_workers' limit, leader
- * autovacuum process must call this function during computing the parallel
- * degree.
+ * Reserves parallel workers for autovacuum.
  *
- * 'nworkers' is the desired number of parallel workers to reserve. Function
- * sets 'nworkers' to the number of parallel workers that actually can be
- * launched and reserves these workers (if any) in global autovacuum state.
- *
- * NOTE: We will try to provide as many workers as requested, even if caller
- * will occupy all available workers.
+ * nworkers is an in/out parameter; the requested number of parallel workers
+ * to reserve by the caller, and set to the actual number of reserved workers.
  */
 void
 AutoVacuumReserveParallelWorkers(int *nworkers)
 {
-	/* Only leader worker can call this function. */
+	/* Only leader autovacuum worker can call this function. */
 	Assert(AmAutoVacuumWorkerProcess() && !IsParallelWorker());
 
-	/*
-	 * We can only reserve workers at the beginning of parallel index
-	 * processing, so we must not have any reserved workers right now.
-	 */
+	/* The worker must not have any reserved workers yet */
 	Assert(av_nworkers_reserved == 0);
 
 	LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
 
 	/* Provide as many workers as we can. */
-	*nworkers= Min(AutoVacuumShmem->av_freeParallelWorkers, *nworkers);
+	*nworkers = Min(AutoVacuumShmem->av_freeParallelWorkers, *nworkers);
 	AutoVacuumShmem->av_freeParallelWorkers -= *nworkers;
 
 	/* Remember how many workers we have reserved. */
@@ -3632,8 +3624,8 @@ check_av_worker_gucs(void)
 }
 
 /*
- * Make sure that number of free parallel workers corresponds to the
- * autovacuum_max_parallel_workers parameter (after it was changed).
+ * Adjusts the number of free parallel workers corresponds to the new
+ * autovacuum_max_parallel_workers value.
  */
 static void
 adjust_free_parallel_workers(int prev_max_parallel_workers)