Disallow the cost balancing code from resulting in a zero cost limit, which

alvherre · alvherre · commit a4d587271914 · 2007-06-08T21:21:28.000Z
causes a division-by-zero error in the vacuum code.  This can happen when there
are more workers than cost limit units.

Per report from Galy Lee in
&lt;200705310914.l4V9E6JA094603@wwwmaster.postgresql.org&gt;.
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.48 2007/06/08 21:09:49 alvherre Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.49 2007/06/08 21:21:28 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1599,7 +1599,11 @@ autovac_balance_cost(void)
 			int     limit = (int)
 				(cost_avail * worker->wi_cost_limit_base / cost_total);
 
-			worker->wi_cost_limit = Min(limit, worker->wi_cost_limit_base);
+			/*
+			 * We put a lower bound of 1 to the cost_limit, to avoid division-
+			 * by-zero in the vacuum code.
+			 */
+			worker->wi_cost_limit = Max(Min(limit, worker->wi_cost_limit_base), 1);
 
 			elog(DEBUG2, "autovac_balance_cost(pid=%u db=%u, rel=%u, cost_limit=%d, cost_delay=%d)",
 				 worker->wi_workerpid, worker->wi_dboid,

Original file line number	Diff line number	Diff line change
`@@ -10,7 +10,7 @@`
`10`	`10`	`*`
`11`	`11`	`*`
`12`	`12`	`* IDENTIFICATION`
`13`		`- * $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.48 2007/06/08 21:09:49 alvherre Exp $`
	`13`	`+ * $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.49 2007/06/08 21:21:28 alvherre Exp $`
`14`	`14`	`*`
`15`	`15`	`*-------------------------------------------------------------------------`
`16`	`16`	`*/`
`@@ -1599,7 +1599,11 @@ autovac_balance_cost(void)`
`1599`	`1599`	`int limit = (int)`
`1600`	`1600`	`(cost_avail * worker->wi_cost_limit_base / cost_total);`
`1601`	`1601`
`1602`		`- worker->wi_cost_limit = Min(limit, worker->wi_cost_limit_base);`
	`1602`	`+ /*`
	`1603`	`+ * We put a lower bound of 1 to the cost_limit, to avoid division-`
	`1604`	`+ * by-zero in the vacuum code.`
	`1605`	`+ */`
	`1606`	`+ worker->wi_cost_limit = Max(Min(limit, worker->wi_cost_limit_base), 1);`
`1603`	`1607`
`1604`	`1608`	`elog(DEBUG2, "autovac_balance_cost(pid=%u db=%u, rel=%u, cost_limit=%d, cost_delay=%d)",`
`1605`	`1609`	`worker->wi_workerpid, worker->wi_dboid,`