Refresh cost-based delay params more frequently in autovacuum

Allow autovacuum to reload the config file more often so that cost-based
delay parameters can take effect while VACUUMing a relation. Previously,
autovacuum workers only reloaded the config file once per relation
vacuumed, so config changes could not take effect until beginning to
vacuum the next table.

Now, check if a reload is pending roughly once per block, when checking
if we need to delay.

In order for autovacuum workers to safely update their own cost delay
and cost limit parameters without impacting performance, we had to
rethink when and how these values were accessed.

Previously, an autovacuum worker's wi_cost_limit was set only at the
beginning of vacuuming a table, after reloading the config file.
Therefore, at the time that autovac_balance_cost() was called, workers
vacuuming tables with no cost-related storage parameters could still
have different values for their wi_cost_limit_base and wi_cost_delay.

Now that the cost parameters can be updated while vacuuming a table,
workers will (within some margin of error) have no reason to have
different values for cost limit and cost delay (in the absence of
cost-related storage parameters). This removes the rationale for keeping
cost limit and cost delay in shared memory. Balancing the cost limit
requires only the number of active autovacuum workers vacuuming a table
with no cost-based storage parameters.

Author: Melanie Plageman <[email protected]>
Reviewed-by: Masahiko Sawada <[email protected]>
Reviewed-by: Daniel Gustafsson <[email protected]>
Reviewed-by: Kyotaro Horiguchi <[email protected]>
Reviewed-by: Robert Haas <[email protected]>
Discussion: https://www.postgresql.org/message-id/flat/CAAKRu_ZngzqnEODc7LmS1NH04Kt6Y9huSjz5pp7%2BDXhrjDA0gw%40mail.gmail.com

1 files changed, 42 insertions, 4 deletions

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index f2be74cdb5f..9386c08a556 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -48,6 +48,7 @@
 #include "pgstat.h"
 #include "postmaster/autovacuum.h"
 #include "postmaster/bgworker_internals.h"
+#include "postmaster/interrupt.h"
 #include "storage/bufmgr.h"
 #include "storage/lmgr.h"
 #include "storage/pmsignal.h"
@@ -523,9 +524,9 @@ vacuum(List *relations, VacuumParams *params, BufferAccessStrategy bstrategy,
 	{
 		ListCell   *cur;
 
-		VacuumUpdateCosts();
 		in_vacuum = true;
-		VacuumCostActive = (vacuum_cost_delay > 0);
+		VacuumFailsafeActive = false;
+		VacuumUpdateCosts();
 		VacuumCostBalance = 0;
 		VacuumPageHit = 0;
 		VacuumPageMiss = 0;
@@ -579,12 +580,20 @@ vacuum(List *relations, VacuumParams *params, BufferAccessStrategy bstrategy,
 					CommandCounterIncrement();
 				}
 			}
+
+			/*
+			 * Ensure VacuumFailsafeActive has been reset before vacuuming the
+			 * next relation.
+			 */
+			VacuumFailsafeActive = false;
 		}
 	}
 	PG_FINALLY();
 	{
 		in_vacuum = false;
 		VacuumCostActive = false;
+		VacuumFailsafeActive = false;
+		VacuumCostBalance = 0;
 	}
 	PG_END_TRY();
 
@@ -2245,7 +2254,28 @@ vacuum_delay_point(void)
 	/* Always check for interrupts */
 	CHECK_FOR_INTERRUPTS();
 
-	if (!VacuumCostActive || InterruptPending)
+	if (InterruptPending ||
+		(!VacuumCostActive && !ConfigReloadPending))
+		return;
+
+	/*
+	 * Autovacuum workers should reload the configuration file if requested.
+	 * This allows changes to [autovacuum_]vacuum_cost_limit and
+	 * [autovacuum_]vacuum_cost_delay to take effect while a table is being
+	 * vacuumed or analyzed.
+	 */
+	if (ConfigReloadPending && IsAutoVacuumWorkerProcess())
+	{
+		ConfigReloadPending = false;
+		ProcessConfigFile(PGC_SIGHUP);
+		VacuumUpdateCosts();
+	}
+
+	/*
+	 * If we disabled cost-based delays after reloading the config file,
+	 * return.
+	 */
+	if (!VacuumCostActive)
 		return;
 
 	/*
@@ -2278,7 +2308,15 @@ vacuum_delay_point(void)
 
 		VacuumCostBalance = 0;
 
-		VacuumUpdateCosts();
+		/*
+		 * Balance and update limit values for autovacuum workers. We must do
+		 * this periodically, as the number of workers across which we are
+		 * balancing the limit may have changed.
+		 *
+		 * TODO: There may be better criteria for determining when to do this
+		 * besides "check after napping".
+		 */
+		AutoVacuumUpdateCostLimit();
 
 		/* Might have gotten an interrupt while sleeping */
 		CHECK_FOR_INTERRUPTS();