Reduce the initial size of local lock hash to 16 entries.

hlinnaka · hlinnaka · commit 4c37c1e3b2a7 · 2011-04-15T15:07:36.000+03:00
The hash table is seq scanned at transaction end, to release all locks,
and making the hash table larger than necessary makes that slower. With
very simple queries, that overhead can amount to a few percent of the total
CPU time used.

At the moment, backend startup needs 6 locks, and a simple query with one
table and index needs 3 locks. 16 is enough for even quite complicated
transactions, and it will grow automatically if it fills up.
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
@@ -346,7 +346,7 @@ InitLocks(void)
 	hash_flags = (HASH_ELEM | HASH_FUNCTION);
 
 	LockMethodLocalHash = hash_create("LOCALLOCK hash",
-									  128,
+									  16,
 									  &info,
 									  hash_flags);
 }

Original file line number	Diff line number	Diff line change
`@@ -346,7 +346,7 @@ InitLocks(void)`
`346`	`346`	`hash_flags = (HASH_ELEM \| HASH_FUNCTION);`
`347`	`347`
`348`	`348`	`LockMethodLocalHash = hash_create("LOCALLOCK hash",`
`349`		`- 128,`
	`349`	`+ 16,`
`350`	`350`	`&info,`
`351`	`351`	`hash_flags);`
`352`	`352`	`}`