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Use conditional variable to wait for next MultiXact offset

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In one multixact.c edge case, we need a mechanism to wait for one
multixact offset to be written before being allowed to read the next
one.  We used to handle this case by sleeping for one millisecond and
retrying, but such sleeps have been reported as problematic in
production cases.  We can avoid the problem by using a condition
variable: readers sleep on it and then every creator of multixacts
broadcasts into the CV when creation is sufficiently far along.

Author: Kyotaro Horiguchi <horikyotajntt@gmail.com>
Reviewed-by: Andrey Borodin <amborodin@acm.org>
Discussion: https://postgr.es/m/47A598F4-B4E7-4029-8FEC-A06A6C3CB4B5@yandex-team.ru
Discussion: https://postgr.es/m/20200515.090333.24867479329066911.horikyota.ntt
This commit is contained in:
Alvaro Herrera
2024-04-07 20:33:45 +02:00
parent 473411fc51
commit a0e0fb1ba5
2 changed files with 29 additions and 2 deletions
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src/backend/utils/activity/wait_event_names.txt
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@@ -139,6 +139,7 @@ MESSAGE_QUEUE_INTERNAL "Waiting for another process to be attached to a shared m
MESSAGE_QUEUE_PUT_MESSAGE "Waiting to write a protocol message to a shared message queue."
MESSAGE_QUEUE_RECEIVE "Waiting to receive bytes from a shared message queue."
MESSAGE_QUEUE_SEND "Waiting to send bytes to a shared message queue."
MULTIXACT_CREATION "Waiting for a multixact creation to complete."
PARALLEL_BITMAP_SCAN "Waiting for parallel bitmap scan to become initialized."
PARALLEL_CREATE_INDEX_SCAN "Waiting for parallel <command>CREATE INDEX</command> workers to finish heap scan."
PARALLEL_FINISH "Waiting for parallel workers to finish computing."