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Andres Freund a4adc31f69 lwlock: Fix quadratic behavior with very long wait lists ... Until now LWLockDequeueSelf() sequentially searched the list of waiters to see if the current proc is still is on the list of waiters, or has already been removed. In extreme workloads, where the wait lists are very long, this leads to a quadratic behavior. #backends iterating over a list #backends long. Additionally, the likelihood of needing to call LWLockDequeueSelf() in the first place also increases with the increased length of the wait queue, as it becomes more likely that a lock is released while waiting for the wait list lock, which is held for longer during lock release. Due to the exponential back-off in perform_spin_delay() this is surprisingly hard to detect. We should make that easier, e.g. by adding a wait event around the pg_usleep() - but that's a separate patch. The fix is simple - track whether a proc is currently waiting in the wait list or already removed but waiting to be woken up in PGPROC->lwWaiting. In some workloads with a lot of clients contending for a small number of lwlocks (e.g. WALWriteLock), the fix can substantially increase throughput. As the quadratic behavior arguably is a bug, we might want to decide to backpatch this fix in the future. Author: Andres Freund <andres@anarazel.de> Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> Discussion: https://postgr.es/m/20221027165914.2hofzp4cvutj6gin@awork3.anarazel.de Discussion: https://postgr.es/m/CALj2ACXktNbG=K8Xi7PSqbofTZozavhaxjatVc14iYaLu4Maag@mail.gmail.com		3 years ago
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brin	Refactor ownercheck functions	3 years ago
common	Refactor aclcheck functions	3 years ago
gin	Refactor ownercheck functions	3 years ago
gist	Standardize rmgrdesc recovery conflict XID output.	3 years ago
hash	Standardize rmgrdesc recovery conflict XID output.	3 years ago
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rmgrdesc	Standardize rmgrdesc recovery conflict XID output.	3 years ago
spgist	Standardize rmgrdesc recovery conflict XID output.	3 years ago
table	meson: Add initial version of meson based build system	3 years ago
tablesample	meson: Add initial version of meson based build system	3 years ago
transam	lwlock: Fix quadratic behavior with very long wait lists	3 years ago
Makefile	…
meson.build	meson: Add initial version of meson based build system	3 years ago