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Clamp the output of estimate_hash_bucketsize() to a sane range;

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per example from Bruno Wolff in which it produced a silly result.
This commit is contained in:
Tom Lane 2002-12-26 23:38:42 +00:00
parent 1dfbbd51e7
commit f772e6cbf7
1 changed files with 11 additions and 1 deletions
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12
src/backend/optimizer/path/costsize.c
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@ -42,7 +42,7 @@
* Portions Copyright (c) 1994, Regents of the University of California * Portions Copyright (c) 1994, Regents of the University of California
* *
* IDENTIFICATION * IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.96 2002/12/14 00:17:55 tgl Exp $ * $Header: /cvsroot/pgsql/src/backend/optimizer/path/costsize.c,v 1.97 2002/12/26 23:38:42 tgl Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -1164,6 +1164,16 @@ estimate_hash_bucketsize(Query *root, Var *var)
if (avgfreq > 0.0 && mcvfreq > avgfreq) if (avgfreq > 0.0 && mcvfreq > avgfreq)
estfract *= mcvfreq / avgfreq; estfract *= mcvfreq / avgfreq;
/*
* Clamp bucketsize to sane range (the above adjustment could easily
* produce an out-of-range result). We set the lower bound a little
* above zero, since zero isn't a very sane result.
*/
if (estfract < 1.0e-6)
estfract = 1.0e-6;
else if (estfract > 1.0)
estfract = 1.0;
ReleaseSysCache(tuple); ReleaseSysCache(tuple);
return (Selectivity) estfract; return (Selectivity) estfract;