Fix calculation in brin_minmax_multi_distance_date
When calculating the distance between date values, make sure to subtract
them in the right order, i.e. (larger - smaller).
The distance is used to determine which values to merge, and is expected
to be a positive value. The code unfortunately did the subtraction in
the opposite order, i.e. (smaller - larger), thus producing negative
values and merging values the most distant values first.
The resulting index is correct (i.e. produces correct results), but may
be significantly less efficient. This affects all minmax-multi indexes
on date columns.
Backpatch to 14, where minmax-multi indexes were introduced.
Reported-by: Ashutosh Bapat
Reviewed-by: Ashutosh Bapat, Dean Rasheed
Backpatch-through: 14
Discussion: https://postgr.es/m/eef0ea8c-4aaa-8d0d-027f-58b1f35dd170@enterprisedb.com
Branch
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REL_14_STABLE
Details
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https://git.postgresql.org/pg/commitdiff/d1740e169d950d457907bbfa32f39f79c8504e20
Modified Files
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src/backend/access/brin/brin_minmax_multi.c | 7 ++++++-
src/test/regress/expected/brin_multi.out | 20 ++++++++++++++++++++
src/test/regress/sql/brin_multi.sql | 18 ++++++++++++++++++
3 files changed, 44 insertions(+), 1 deletion(-)