Separate vacuum cost variables from GUCs

Vacuum code run both by autovacuum workers and a backend doing
VACUUM/ANALYZE previously inspected VacuumCostLimit and VacuumCostDelay,
which are the global variables backing the GUCs vacuum_cost_limit and
vacuum_cost_delay.

Autovacuum workers needed to override these variables with their
own values, derived from autovacuum_vacuum_cost_limit and
autovacuum_vacuum_cost_delay and worker cost limit balancing logic.
This led to confusing code which, in some cases, both derived and
set a new value of VacuumCostLimit from VacuumCostLimit.

In preparation for refreshing these GUC values more often, introduce
new, independent global variables and add a function to update them
using the GUCs and existing logic.

Per suggestion by Kyotaro Horiguchi

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CAAKRu_ZngzqnEODc7LmS1NH04Kt6Y9huSjz5pp7%2BDXhrjDA0gw%40mail.gmail.com

src/backend/commands/vacuum.c

@@ -72,6 +72,15 @@ int			vacuum_multixact_freeze_table_age;
 int			vacuum_failsafe_age;
 int			vacuum_multixact_failsafe_age;
 
+/*
+ * Variables for cost-based vacuum delay. The defaults differ between
+ * autovacuum and vacuum. They should be set with the appropriate GUC value in
+ * vacuum code. They are initialized here to the defaults for client backends
+ * executing VACUUM or ANALYZE.
+ */
+double		vacuum_cost_delay = 0;
+int			vacuum_cost_limit = 200;
+
 /*
  * VacuumFailsafeActive is a defined as a global so that we can determine
  * whether or not to re-enable cost-based vacuum delay when vacuuming a table.
@@ -514,8 +523,9 @@ vacuum(List *relations, VacuumParams *params, BufferAccessStrategy bstrategy,
 	{
 		ListCell   *cur;
 
+		VacuumUpdateCosts();
 		in_vacuum = true;
-		VacuumCostActive = (VacuumCostDelay > 0);
+		VacuumCostActive = (vacuum_cost_delay > 0);
 		VacuumCostBalance = 0;
 		VacuumPageHit = 0;
 		VacuumPageMiss = 0;
@@ -2244,14 +2254,14 @@ vacuum_delay_point(void)
 	 */
 	if (VacuumSharedCostBalance != NULL)
 		msec = compute_parallel_delay();
-	else if (VacuumCostBalance >= VacuumCostLimit)
-		msec = VacuumCostDelay * VacuumCostBalance / VacuumCostLimit;
+	else if (VacuumCostBalance >= vacuum_cost_limit)
+		msec = vacuum_cost_delay * VacuumCostBalance / vacuum_cost_limit;
 
 	/* Nap if appropriate */
 	if (msec > 0)
 	{
-		if (msec > VacuumCostDelay * 4)
-			msec = VacuumCostDelay * 4;
+		if (msec > vacuum_cost_delay * 4)
+			msec = vacuum_cost_delay * 4;
 
 		pgstat_report_wait_start(WAIT_EVENT_VACUUM_DELAY);
 		pg_usleep(msec * 1000);
@@ -2268,8 +2278,7 @@ vacuum_delay_point(void)
 
 		VacuumCostBalance = 0;
 
-		/* update balance values for workers */
-		AutoVacuumUpdateDelay();
+		VacuumUpdateCosts();
 
 		/* Might have gotten an interrupt while sleeping */
 		CHECK_FOR_INTERRUPTS();
@@ -2319,11 +2328,11 @@ compute_parallel_delay(void)
 	/* Compute the total local balance for the current worker */
 	VacuumCostBalanceLocal += VacuumCostBalance;
 
-	if ((shared_balance >= VacuumCostLimit) &&
-		(VacuumCostBalanceLocal > 0.5 * ((double) VacuumCostLimit / nworkers)))
+	if ((shared_balance >= vacuum_cost_limit) &&
+		(VacuumCostBalanceLocal > 0.5 * ((double) vacuum_cost_limit / nworkers)))
 	{
 		/* Compute sleep time based on the local cost balance */
-		msec = VacuumCostDelay * VacuumCostBalanceLocal / VacuumCostLimit;
+		msec = vacuum_cost_delay * VacuumCostBalanceLocal / vacuum_cost_limit;
 		pg_atomic_sub_fetch_u32(VacuumSharedCostBalance, VacuumCostBalanceLocal);
 		VacuumCostBalanceLocal = 0;
 	}

src/backend/commands/vacuumparallel.c

@@ -995,7 +995,8 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
 												 false);
 
 	/* Set cost-based vacuum delay */
-	VacuumCostActive = (VacuumCostDelay > 0);
+	VacuumCostActive = (vacuum_cost_delay > 0);
+	VacuumUpdateCosts();
 	VacuumCostBalance = 0;
 	VacuumPageHit = 0;
 	VacuumPageMiss = 0;

src/backend/postmaster/autovacuum.c

@@ -1773,16 +1773,24 @@ FreeWorkerInfo(int code, Datum arg)
 }
 
 /*
- * Update the cost-based delay parameters, so that multiple workers consume
- * each a fraction of the total available I/O.
+ * Update vacuum cost-based delay-related parameters for autovacuum workers and
+ * backends executing VACUUM or ANALYZE using the value of relevant GUCs and
+ * global state. This must be called during setup for vacuum and after every
+ * config reload to ensure up-to-date values.
  */
 void
-AutoVacuumUpdateDelay(void)
+VacuumUpdateCosts(void)
 {
 	if (MyWorkerInfo)
 	{
-		VacuumCostDelay = MyWorkerInfo->wi_cost_delay;
-		VacuumCostLimit = MyWorkerInfo->wi_cost_limit;
+		vacuum_cost_delay = MyWorkerInfo->wi_cost_delay;
+		vacuum_cost_limit = MyWorkerInfo->wi_cost_limit;
+	}
+	else
+	{
+		/* Must be explicit VACUUM or ANALYZE */
+		vacuum_cost_delay = VacuumCostDelay;
+		vacuum_cost_limit = VacuumCostLimit;
 	}
 }
 
@@ -2311,8 +2319,6 @@ do_autovacuum(void)
 		autovac_table *tab;
 		bool		isshared;
 		bool		skipit;
-		double		stdVacuumCostDelay;
-		int			stdVacuumCostLimit;
 		dlist_iter	iter;
 
 		CHECK_FOR_INTERRUPTS();
@@ -2415,14 +2421,6 @@ do_autovacuum(void)
 			continue;
 		}
 
-		/*
-		 * Remember the prevailing values of the vacuum cost GUCs.  We have to
-		 * restore these at the bottom of the loop, else we'll compute wrong
-		 * values in the next iteration of autovac_balance_cost().
-		 */
-		stdVacuumCostDelay = VacuumCostDelay;
-		stdVacuumCostLimit = VacuumCostLimit;
-
 		/* Must hold AutovacuumLock while mucking with cost balance info */
 		LWLockAcquire(AutovacuumLock, LW_EXCLUSIVE);
 
@@ -2436,7 +2434,7 @@ do_autovacuum(void)
 		autovac_balance_cost();
 
 		/* set the active cost parameters from the result of that */
-		AutoVacuumUpdateDelay();
+		VacuumUpdateCosts();
 
 		/* done */
 		LWLockRelease(AutovacuumLock);
@@ -2533,10 +2531,6 @@ deleted:
 		MyWorkerInfo->wi_tableoid = InvalidOid;
 		MyWorkerInfo->wi_sharedrel = false;
 		LWLockRelease(AutovacuumScheduleLock);
-
-		/* restore vacuum cost GUCs for the next iteration */
-		VacuumCostDelay = stdVacuumCostDelay;
-		VacuumCostLimit = stdVacuumCostLimit;
 	}
 
 	/*

src/include/commands/vacuum.h

@@ -307,6 +307,8 @@ extern PGDLLIMPORT pg_atomic_uint32 *VacuumActiveNWorkers;
 extern PGDLLIMPORT int VacuumCostBalanceLocal;
 
 extern PGDLLIMPORT bool VacuumFailsafeActive;
+extern PGDLLIMPORT double vacuum_cost_delay;
+extern PGDLLIMPORT int vacuum_cost_limit;
 
 /* in commands/vacuum.c */
 extern void ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel);
@@ -347,6 +349,9 @@ extern IndexBulkDeleteResult *vac_cleanup_one_index(IndexVacuumInfo *ivinfo,
 													IndexBulkDeleteResult *istat);
 extern Size vac_max_items_to_alloc_size(int max_items);
 
+/* In postmaster/autovacuum.c */
+extern void VacuumUpdateCosts(void);
+
 /* in commands/vacuumparallel.c */
 extern ParallelVacuumState *parallel_vacuum_init(Relation rel, Relation *indrels,
 												 int nindexes, int nrequested_workers,

src/include/postmaster/autovacuum.h

@@ -63,9 +63,6 @@ extern int	StartAutoVacWorker(void);
 /* called from postmaster when a worker could not be forked */
 extern void AutoVacWorkerFailed(void);
 
-/* autovacuum cost-delay balancer */
-extern void AutoVacuumUpdateDelay(void);
-
 #ifdef EXEC_BACKEND
 extern void AutoVacLauncherMain(int argc, char *argv[]) pg_attribute_noreturn();
 extern void AutoVacWorkerMain(int argc, char *argv[]) pg_attribute_noreturn();