Horton

Re: inefficient loop in StandbyReleaseLockList()

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>, sulamul@gmail.com, bossartn@amazon.com, pgsql-hackers@postgresql.org
Date: 2021-10-28T22:24:51Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> Which leads to to wonder whether the better fix would be to switch to deleting
> the last element, but still use the while (!empty) style. That should convert
> the O(n^2) due to 1cff1b9 back to O(n). It might or might not be faster/slower
> than using foreach(), but it should be within the same ballpark.

Does it matter what order we're releasing the locks in?

			regards, tom lane

Commits

  1. Doc: add some notes about performance of the List functions.

  2. Avoid O(N^2) behavior in SyncPostCheckpoint().

  3. Avoid some other O(N^2) hazards in list manipulation.

  4. Avoid O(N^2) behavior when the standby process releases many locks.