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Marginal hack to avoid spending a lot of time in find_join_rel during

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large planning problems: when the list of join rels gets too long, make
an auxiliary hash table that hashes on the identifying Bitmapset.
This commit is contained in:
Tom Lane
2005-06-08 23:02:05 +00:00
parent 77c168a836
commit e3a33a9a9f
9 changed files with 194 additions and 25 deletions
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27
src/backend/nodes/bitmapset.c
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@ -14,7 +14,7 @@
* Copyright (c) 2003-2005, PostgreSQL Global Development Group
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/nodes/bitmapset.c,v 1.7 2005/01/01 20:44:15 tgl Exp $
* $PostgreSQL: pgsql/src/backend/nodes/bitmapset.c,v 1.8 2005/06/08 23:02:04 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -763,3 +763,28 @@ bms_first_member(Bitmapset *a)
}
return -1;
}
/*
* bms_hash_value - compute a hash key for a Bitmapset
*
* Note: we must ensure that any two bitmapsets that are bms_equal() will
* hash to the same value; in practice this means that trailing all-zero
* words cannot affect the result. Longitudinal XOR provides a reasonable
* hash value that has this property.
*/
uint32
bms_hash_value(const Bitmapset *a)
{
bitmapword result = 0;
int nwords;
int wordnum;
if (a == NULL)
return 0; /* All empty sets hash to 0 */
nwords = a->nwords;
for (wordnum = 0; wordnum < nwords; wordnum++)
{
result ^= a->words[wordnum];
}
return (uint32) result;
}