pgsql: Fix tsmatchsel() to account properly for null rows.

Fix tsmatchsel() to account properly for null rows.

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

Branch
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REL8_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/2b3a0630b54ff9970a7cd2c78a686015f9a53c0c

Modified Files
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src/backend/tsearch/ts_selfuncs.c | 6 ++++++
src/include/catalog/pg_statistic.h | 2 ++
2 files changed, 8 insertions(+), 0 deletions(-)