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

2 files changed, 21 insertions, 11 deletions

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 7fc5c19e379..f2be74cdb5f 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -73,6 +73,15 @@ 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.
  * If failsafe mode has been engaged, we will not re-enable cost-based delay
@@ -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;
 	}
diff --git a/src/backend/commands/vacuumparallel.c b/src/backend/commands/vacuumparallel.c
index 563117a8f6e..cc0aff79044 100644
--- a/src/backend/commands/vacuumparallel.c
+++ b/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;