Improve eqjoinsel's ndistinct clamping to work for multiple levels of join.
This patch fixes an oversight in my commit
7f3eba30c9d622d1981b1368f2d79ba0999cdff2 of 2008-10-23. That patch
accounted for baserel restriction clauses that reduced the number of rows
coming out of a table (and hence the number of possibly-distinct values of
a join variable), but not for join restriction clauses that might have been
applied at a lower level of join. To account for the latter, look up the
sizes of the min_lefthand and min_righthand inputs of the current join,
and clamp with those in the same way as for the base relations.
Noted while investigating a complaint from Ben Chobot, although this in
itself doesn't seem to explain his report.
Back-patch to 8.4; previous versions used different estimation methods
for which this heuristic isn't relevant.
Branch
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REL9_0_STABLE
Details
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http://git.postgresql.org/pg/commitdiff/53434c6f0dfa89bf287fadbde26b050b043c0c94
Modified Files
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src/backend/utils/adt/selfuncs.c | 81 ++++++++++++++++++++++++++++++++++----
1 files changed, 73 insertions(+), 8 deletions(-)