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Fix tsmatchsel() to account properly for null rows.

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ts_typanalyze.c computes MCE statistics as fractions of the non-null rows,
which seems fairly reasonable, and anyway changing it in released versions
wouldn't be a good idea.  But then ts_selfuncs.c has to account for that.
Failure to do so results in overestimates in columns with a significant
fraction of null documents.  Back-patch to 8.4 where this stuff was
introduced.

Jesper Krogh
This commit is contained in:
Tom Lane
2011-02-17 19:00:49 -05:00
parent de623f3335
commit 52b60530f2
2 changed files with 8 additions and 0 deletions
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6
src/backend/tsearch/ts_selfuncs.c
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@ -189,11 +189,17 @@ tsquerysel(VariableStatData *vardata, Datum constval)
/* No most-common-elements info, so do without */
selec = tsquery_opr_selec_no_stats(query);
}
/*
* MCE stats count only non-null rows, so adjust for null rows.
*/
selec *= (1.0 - stats->stanullfrac);
}
else
{
/* No stats at all, so do without */
selec = tsquery_opr_selec_no_stats(query);
/* we assume no nulls here, so no stanullfrac correction */
}
return selec;