pgsql: Move RecoveryLockList into a hash table.

Move RecoveryLockList into a hash table.

Standbys frequently need to release all locks held by a given xid.
Instead of searching one big list linearly, let's create one list
per xid and put them in a hash table, so we can find what we need
in O(1) time.

Earlier analysis and a prototype were done by David Rowley, though
this isn't his patch.

Back-patch all the way.

Author: Thomas Munro
Diagnosed-by: David Rowley, Andres Freund
Reviewed-by: Andres Freund, Tom Lane, Robert Haas
Discussion: https://postgr.es/m/CAEepm%3D1mL0KiQ2KJ4yuPpLGX94a4Ns_W6TL4EGRouxWibu56pA%40mail.gmail.com
Discussion: https://postgr.es/m/CAKJS1f9vJ841HY%3DwonnLVbfkTWGYWdPN72VMxnArcGCjF3SywA%40mail.gmail.com

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/35750a38b7ab6e30aa2ee6eb7765ebd2172dd7c5

Modified Files
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src/backend/storage/ipc/standby.c | 164 ++++++++++++++++++++------------------
1 file changed, 87 insertions(+), 77 deletions(-)