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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 19:01:01 -05:00
parent 42e663cc41
commit 2b3a0630b5
2 changed files with 8 additions and 0 deletions
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6
src/backend/tsearch/ts_selfuncs.c
View File

@ -188,11 +188,17 @@ tsquerysel(VariableStatData *vardata, Datum constval)
/* No most-common-elements info, so do without */ /* No most-common-elements info, so do without */
selec = tsquery_opr_selec_no_stats(query); 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 else
{ {
/* No stats at all, so do without */ /* No stats at all, so do without */
selec = tsquery_opr_selec_no_stats(query); selec = tsquery_opr_selec_no_stats(query);
/* we assume no nulls here, so no stanullfrac correction */
} }
return selec; return selec;

2
src/include/catalog/pg_statistic.h
View File

@ -244,6 +244,8 @@ typedef FormData_pg_statistic *Form_pg_statistic;
* type with identifiable elements (for instance, tsvector). staop contains * type with identifiable elements (for instance, tsvector). staop contains
* the equality operator appropriate to the element type. stavalues contains * the equality operator appropriate to the element type. stavalues contains
* the most common element values, and stanumbers their frequencies. Unlike * the most common element values, and stanumbers their frequencies. Unlike
* MCV slots, frequencies are measured as the fraction of non-null rows the
* element value appears in, not the frequency of all rows. Also unlike
* MCV slots, the values are sorted into order (to support binary search * MCV slots, the values are sorted into order (to support binary search
* for a particular value). Since this puts the minimum and maximum * for a particular value). Since this puts the minimum and maximum
* frequencies at unpredictable spots in stanumbers, there are two extra * frequencies at unpredictable spots in stanumbers, there are two extra