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Reduce eqsel()'s fudge-factor for estimating the frequency of values

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other than the most common value in a column.  We had had 0.5, make it
0.1 to make it more likely that an indexscan will be chosen.  Really
need better statistics instead, but this should stem the bleeding
meanwhile ...
This commit is contained in:
Tom Lane 2000-05-26 17:19:15 +00:00
parent be6e7717db
commit b71761d280
1 changed files with 6 additions and 3 deletions
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9
src/backend/utils/adt/selfuncs.c
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@ -15,7 +15,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.65 2000/04/16 04:41:02 tgl Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.66 2000/05/26 17:19:15 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -55,6 +55,9 @@
/* default selectivity estimate for pattern-match operators such as LIKE */
#define DEFAULT_MATCH_SEL 0.01
/* "fudge factor" for estimating frequency of not-most-common values */
#define NOT_MOST_COMMON_RATIO 0.1
static bool convert_to_scalar(Datum value, Oid valuetypid, double *scaledvalue,
Datum lobound, Datum hibound, Oid boundstypid,
double *scaledlobound, double *scaledhibound);
@ -190,7 +193,7 @@ eqsel(Oid opid,
* exactly!
*/
if (typid != BOOLOID)
selec *= 0.5;
selec *= NOT_MOST_COMMON_RATIO;
}
}
else
@ -209,7 +212,7 @@ eqsel(Oid opid,
* and in fact it's probably less, so apply a fudge
* factor.
*/
selec *= 0.5;
selec *= NOT_MOST_COMMON_RATIO;
}
/* result should be in range, but make sure... */