pgsql: Optimize allocations in bringetbitmap

Optimize allocations in bringetbitmap

The bringetbitmap function allocates memory for various purposes, which
may be quite expensive, depending on the number of scan keys. Instead of
allocating them separately, allocate one bit chunk of memory an carve it
into smaller pieces as needed - all the pieces have the same lifespan,
and it saves quite a bit of CPU and memory overhead.

Author: Tomas Vondra <tomas(dot)vondra(at)postgresql(dot)org>
Reviewed-by: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Reviewed-by: Mark Dilger <hornschnorter(at)gmail(dot)com>
Reviewed-by: Alexander Korotkov <aekorotkov(at)gmail(dot)com>
Reviewed-by: Masahiko Sawada <masahiko(dot)sawada(at)enterprisedb(dot)com>
Reviewed-by: John Naylor <john(dot)naylor(at)enterprisedb(dot)com>
Discussion: https://postgr.es/m/c1138ead-7668-f0e1-0638-c3be3237e812@2ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8e4b332e88b8339408a3aa8c62bc93d96b67c808

Modified Files
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src/backend/access/brin/brin.c | 60 +++++++++++++++++++++++++++++++++---------
1 file changed, 47 insertions(+), 13 deletions(-)