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Commitbfd1ffa

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Change patternsel (LIKE/regex selectivity estimation) so that if there
is a large enough histogram, it will use the number of matches in thehistogram to derive a selectivity estimate, rather than the admittedlypretty bogus heuristics involving examining the pattern contents. I set'large enough' at 100, but perhaps we should change that later. Alsoapply the same technique in contrib/ltree's <@ and @> estimator. Perdiscussion with Stefan Kaltenbrunner and Matteo Beccati.
1 parent06b33f0 commitbfd1ffa

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3 files changed

+242
-113
lines changed

3 files changed

+242
-113
lines changed

‎contrib/ltree/ltree_op.c‎

Lines changed: 36 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1,13 +1,14 @@
11
/*
22
* op function for ltree
33
* Teodor Sigaev <teodor@stack.net>
4-
* $PostgreSQL: pgsql/contrib/ltree/ltree_op.c,v 1.12 2006/05/30 22:12:13 tgl Exp $
4+
* $PostgreSQL: pgsql/contrib/ltree/ltree_op.c,v 1.13 2006/09/20 19:50:21 tgl Exp $
55
*/
66

77
#include"ltree.h"
88

99
#include<ctype.h>
1010

11+
#include"catalog/pg_statistic.h"
1112
#include"utils/lsyscache.h"
1213
#include"utils/selfuncs.h"
1314
#include"utils/syscache.h"
@@ -606,6 +607,7 @@ ltreeparentsel(PG_FUNCTION_ARGS)
606607
FmgrInfocontproc;
607608
doublemcvsum;
608609
doublemcvsel;
610+
doublenullfrac;
609611

610612
fmgr_info(get_opcode(operator),&contproc);
611613

@@ -616,10 +618,40 @@ ltreeparentsel(PG_FUNCTION_ARGS)
616618
&mcvsum);
617619

618620
/*
619-
* We have the exact selectivity for values appearing in the MCV list;
620-
* use the default selectivity for the rest of the population.
621+
* If the histogram is large enough, see what fraction of it the
622+
* constant is "<@" to, and assume that's representative of the
623+
* non-MCV population. Otherwise use the default selectivity for
624+
* the non-MCV population.
621625
*/
622-
selec=mcvsel+DEFAULT_PARENT_SEL* (1.0-mcvsum);
626+
selec=histogram_selectivity(&vardata,&contproc,
627+
constval,varonleft,
628+
100,1);
629+
if (selec<0)
630+
{
631+
/* Nope, fall back on default */
632+
selec=DEFAULT_PARENT_SEL;
633+
}
634+
else
635+
{
636+
/* Yes, but don't believe extremely small or large estimates. */
637+
if (selec<0.0001)
638+
selec=0.0001;
639+
elseif (selec>0.9999)
640+
selec=0.9999;
641+
}
642+
643+
if (HeapTupleIsValid(vardata.statsTuple))
644+
nullfrac= ((Form_pg_statistic)GETSTRUCT(vardata.statsTuple))->stanullfrac;
645+
else
646+
nullfrac=0.0;
647+
648+
/*
649+
* Now merge the results from the MCV and histogram calculations,
650+
* realizing that the histogram covers only the non-null values that
651+
* are not listed in MCV.
652+
*/
653+
selec *=1.0-nullfrac-mcvsum;
654+
selec+=mcvsel;
623655
}
624656
else
625657
selec=DEFAULT_PARENT_SEL;

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