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Change patternsel() so that instead of switching from a pure

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pattern-examination heuristic method to purely histogram-driven selectivity at
histogram size 100, we compute both estimates and use a weighted average.
The weight put on the heuristic estimate decreases linearly with histogram
size, dropping to zero for 100 or more histogram entries.
Likewise in ltreeparentsel().  After a patch by Greg Stark, though I
reorganized the logic a bit to give the caller of histogram_selectivity()
more control.
This commit is contained in:
Tom Lane
2008-03-09 00:32:09 +00:00
parent 422495d0da
commit f4230d2937
3 changed files with 75 additions and 35 deletions
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5
src/include/utils/selfuncs.h
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@@ -8,7 +8,7 @@
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/utils/selfuncs.h,v 1.43 2008/01/01 19:45:59 momjian Exp $
* $PostgreSQL: pgsql/src/include/utils/selfuncs.h,v 1.44 2008/03/09 00:32:09 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -112,7 +112,8 @@ extern double mcv_selectivity(VariableStatData *vardata, FmgrInfo *opproc,
double *sumcommonp);
extern double histogram_selectivity(VariableStatData *vardata, FmgrInfo *opproc,
Datum constval, bool varonleft,
int min_hist_size, int n_skip);
int min_hist_size, int n_skip,
int *hist_size);
extern Pattern_Prefix_Status pattern_fixed_prefix(Const *patt,
Pattern_Type ptype,