pgsql: Logical Tape Set: use min heap for freelist.

Logical Tape Set: use min heap for freelist.

Previously, the freelist of blocks was tracked as an
occasionally-sorted array. A min heap is more resilient to larger
freelists or more frequent changes between reading and writing.

Discussion: https://postgr.es/m/97c46a59c27f3c38e486ca170fcbc618d97ab049.camel%40j-davis.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c02fdc9223015c5c386abfa00c47fc7f4c845161

Modified Files
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src/backend/utils/sort/logtape.c | 160 +++++++++++++++++++++++++--------------
1 file changed, 104 insertions(+), 56 deletions(-)