Support boolean columns in functional-dependency statistics

Enterprise / PostgreSQL - Tom Lane [sss.pgh.pa.us] - 4 December 2017 16:51 EST

There's no good reason that the multicolumn stats stuff shouldn't work on booleans. But it looked only for "Var = pseudoconstant" clauses, and it will seldom find those for boolean Vars, since earlier phases of planning will fold "boolvar = true" or "boolvar = false" to just "boolvar" or "NOT boolvar" respectively. Improve dependencies_clauselist_selectivity() to recognize such clauses as equivalent to equality restrictions.

This fixes a failure of the extended stats mechanism to apply in a case reported by Vitaliy Garnashevich. It's not a complete solution to his problem because the bitmap-scan costing code isn't consulting extended stats where it should, but that's surely an independent issue.

In passing, improve some comments, get rid of a NumRelids() test that's redundant with the preceding bms_membership() test, and fix dependencies_clauselist_selectivity() so that estimatedclauses actually is a pure output argument as stated by its API contract.

Back-patch to v10 where this code was introduced.

Discussion: https://postgr.es/m/73a4936d-2814-dc08-ed0c-978f76f435b0@gmail.com

ecc27d55f4 Support boolean columns in functional-dependency statistics.
src/backend/statistics/dependencies.c | 110 +++++++++++++++++++---------------
1 file changed, 63 insertions(+), 47 deletions(-)

Upstream: git.postgresql.org


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