pgsql: Fix BRIN cost estimation

Fix BRIN cost estimation

The original code was overly optimistic about the cost of scanning a
BRIN index, leading to BRIN indexes being selected when they'd be a
worse choice than some other index. This complete rewrite should be
more accurate.

Author: David Rowley, based on an earlier patch by Emre Hasegeli
Reviewed-by: Emre Hasegeli
Discussion: https://postgr.es/m/CAKJS1f9n-Wapop5Xz1dtGdpdqmzeGqQK4sV2MK-zZugfC14Xtw@mail.gmail.com

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/7e534adcdc70866e7be74d626b0ed067c890a251

Modified Files
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src/backend/access/brin/brin.c | 21 ++++
src/backend/utils/adt/selfuncs.c | 197 ++++++++++++++++++++++++++++++++-----
src/include/access/brin.h | 14 +++
src/test/regress/expected/brin.out | 26 +++++
src/test/regress/sql/brin.sql | 16 +++
5 files changed, 248 insertions(+), 26 deletions(-)