Rebased and fixed conflicts. FWIW re: Andrey's comment in his excellent CF summary email[0]: we're currently using vanilla Postgres (via Gentoo) on single nodes, and not anything fancy like Citus. The Citus relationship is just that we were inspired by Marco's blog post there. We have a variety of clients written in different languages that generally don't coordinate their table modifications, and Marco's scheme merely requires them to use sequences idiomatically, which we can just about manage. :-)
This feature is then a performance optimization to support this scheme while avoiding the case where one writer holding a RowExclusiveLock blocks the reader from taking a ShareLock which in turn prevents other writers from taking a RowExclusiveLock for a long time. Instead, the reader can wait for the first writer without taking any locks or blocking later writers. I've illustrated this difference in the isolation tests. Still hoping we can get this into 17. :-) [0] https://www.postgresql.org/message-id/C8D65462-0888-4484-A72C-C99A94381ECD%40yandex-team.ru
v10-0003-Add-pg_wait_for_lockers-function.patch
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v10-0001-Refactor-GetLockConflicts-into-more-general-GetL.patch
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v10-0002-Allow-specifying-single-lockmode-in-WaitForLocke.patch
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