From 40608e7f949fb7e4025c0ddd5be01939adc79eec Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 4 Jan 2010 02:44:40 +0000 Subject: When estimating the selectivity of an inequality "column > constant" or "column < constant", and the comparison value is in the first or last histogram bin or outside the histogram entirely, try to fetch the actual column min or max value using an index scan (if there is an index on the column). If successful, replace the lower or upper histogram bound with that value before carrying on with the estimate. This limits the estimation error caused by moving min/max values when the comparison value is close to the min or max. Per a complaint from Josh Berkus. It is tempting to consider using this mechanism for mergejoinscansel as well, but that would inject index fetches into main-line join estimation not just endpoint cases. I'm refraining from that until we can get a better handle on the costs of doing this type of lookup. --- src/backend/utils/cache/lsyscache.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'src/backend/utils/cache') diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c index cd138c312f0..e68a16c49f9 100644 --- a/src/backend/utils/cache/lsyscache.c +++ b/src/backend/utils/cache/lsyscache.c @@ -7,7 +7,7 @@ * Portions Copyright (c) 1994, Regents of the University of California * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/utils/cache/lsyscache.c,v 1.165 2010/01/02 16:57:55 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/utils/cache/lsyscache.c,v 1.166 2010/01/04 02:44:40 tgl Exp $ * * NOTES * Eventually, the index information should go through here, too. @@ -2577,6 +2577,7 @@ get_attavgwidth(Oid relid, AttrNumber attnum) * atttypmod: typmod of attribute (can be 0 if values == NULL). * reqkind: STAKIND code for desired statistics slot kind. * reqop: STAOP value wanted, or InvalidOid if don't care. + * actualop: if not NULL, *actualop receives the actual STAOP value. * values, nvalues: if not NULL, the slot's stavalues are extracted. * numbers, nnumbers: if not NULL, the slot's stanumbers are extracted. * @@ -2589,6 +2590,7 @@ bool get_attstatsslot(HeapTuple statstuple, Oid atttype, int32 atttypmod, int reqkind, Oid reqop, + Oid *actualop, Datum **values, int *nvalues, float4 **numbers, int *nnumbers) { @@ -2611,6 +2613,9 @@ get_attstatsslot(HeapTuple statstuple, if (i >= STATISTIC_NUM_SLOTS) return false; /* not there */ + if (actualop) + *actualop = (&stats->staop1)[i]; + if (values) { val = SysCacheGetAttr(STATRELATTINH, statstuple, -- cgit v1.2.3