pgsql: Split PGPROC 'links' field into two, for clarity

Split PGPROC 'links' field into two, for clarity

The field was mainly used for the position in a LOCK's wait queue, but
also as the position in a the freelist when the PGPROC entry was not
in use. The reuse saves some memory at the expense of readability,
which seems like a bad tradeoff. If we wanted to make the struct
smaller there's other things we could do, but we're actually just
discussing adding padding to the struct for performance reasons.

Reviewed-by: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/3dd6f70c-b94d-4428-8e75-74a7136396be@iki.fi

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/36bbcd5be3ffee1aa03f69228022decef6ebd37a

Modified Files
--------------
src/backend/access/transam/twophase.c | 2 +-
src/backend/storage/lmgr/deadlock.c | 14 ++++++-------
src/backend/storage/lmgr/lock.c | 6 +++---
src/backend/storage/lmgr/proc.c | 39 ++++++++++++++++++-----------------
src/include/storage/proc.h | 8 +++----
5 files changed, 34 insertions(+), 35 deletions(-)