Commit82b3684

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Add comments spelling out why it's a good idea to release multiple

partition locks in reverse order.

1 parente9e9750 commit82b3684Copy full SHA for 82b3684

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+14

-6

lines changed

+14

-6

lines changed

Lines changed: 8 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.176 2007/02/01 19:10:28 momjian Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.177 2007/07/16 21:09:50 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`* NOTES`
`14`	`14`	`* A lock table is a shared memory hash table. When`
`@@ -2119,7 +2119,13 @@ GetLockStatusData(void)`
`2119`	`2119`	`el++;`
`2120`	`2120`	`}`
`2121`	`2121`
`2122`		`-/* And release locks */`
	`2122`	`+/*`
	`2123`	`+ * And release locks. We do this in reverse order for two reasons:`
	`2124`	`+ * (1) Anyone else who needs more than one of the locks will be trying`
	`2125`	`+ * to lock them in increasing order; we don't want to release the other`
	`2126`	`+ * process until it can get all the locks it needs.`
	`2127`	`+ * (2) This avoids O(N^2) behavior inside LWLockRelease.`
	`2128`	`+ */`
`2123`	`2129`	`for (i=NUM_LOCK_PARTITIONS;--i >=0;)`
`2124`	`2130`	`LWLockRelease(FirstLockMgrLock+i);`
`2125`	`2131`

Lines changed: 6 additions & 4 deletions

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.190 2007/06/19 22:01:15 tgl Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/storage/lmgr/proc.c,v 1.191 2007/07/16 21:09:50 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`*-------------------------------------------------------------------------`
`14`	`14`	`*/`
`@@ -1168,9 +1168,11 @@ CheckDeadLock(void)`
`1168`	`1168`	`}`
`1169`	`1169`
`1170`	`1170`	`/*`
`1171`		`- * Release locks acquired at head of routine. Order is not critical, so`
`1172`		`- * do it back-to-front to avoid waking another CheckDeadLock instance`
`1173`		`- * before it can get all the locks.`
	`1171`	`+ * And release locks. We do this in reverse order for two reasons:`
	`1172`	`+ * (1) Anyone else who needs more than one of the locks will be trying`
	`1173`	`+ * to lock them in increasing order; we don't want to release the other`
	`1174`	`+ * process until it can get all the locks it needs.`
	`1175`	`+ * (2) This avoids O(N^2) behavior inside LWLockRelease.`
`1174`	`1176`	`*/`
`1175`	`1177`	`check_done:`
`1176`	`1178`	`for (i=NUM_LOCK_PARTITIONS;--i >=0;)`

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