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Commit7177bba

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A little further tweaking of the range-query selectivity logic:
to avoid undue sensitivity to roundoff error, believe that a zeroor slightly negative range estimate should represent a smallpositive selectivity, rather than falling back on a generic defaultestimate.
1 parent6d79d60 commit7177bba

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+25
-13
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1 file changed

+25
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‎src/backend/optimizer/path/clausesel.c‎

Lines changed: 25 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/optimizer/path/clausesel.c,v 1.32 2000/03/2300:58:36 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/optimizer/path/clausesel.c,v 1.33 2000/03/2323:35:47 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
@@ -186,20 +186,32 @@ clauselist_selectivity(Query *root,
186186
/* Successfully matched a pair of range clauses */
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Selectivitys2=rqlist->hibound+rqlist->lobound-1.0;
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189-
if (s2>0.0)
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{
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/* All our hard work has paid off! */
192-
s1 *=s2;
193-
}
194-
else
189+
/*
190+
* A zero or slightly negative s2 should be converted into a
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* small positive value; we probably are dealing with a very
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* tight range and got a bogus result due to roundoff errors.
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* However, if s2 is very negative, then we probably have
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* default selectivity estimates on one or both sides of the
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* range. In that case, insert a not-so-wildly-optimistic
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* default estimate.
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*/
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if (s2 <=0.0)
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{
196-
/* One or both is probably a default estimate,
197-
* so supply a default estimate for the selectivity
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* of the range query. We rather optimistically assume
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* that the range is tight...
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*/
201-
s1 *=0.01;
200+
if (s2<-0.01)
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{
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/* No data available --- use a default estimate that
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* is small, but not real small.
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*/
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s2=0.01;
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}
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else
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{
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/* It's just roundoff error; use a small positive value */
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s2=1.0e-10;
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}
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}
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/* Merge in the selectivity of the pair of clauses */
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s1 *=s2;
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}
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else
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{

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