Horton

Re: Using WaitEventSet in the postmaster

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2022-12-05T09:45:57Z
Lists: pgsql-hackers

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On Sat, Dec 3, 2022 at 10:41 AM Thomas Munro <thomas.munro@gmail.com> wrote:
> Here's an iteration like that.  Still WIP grade.  It passes, but there
> must be something I don't understand about this computer program yet,
> because if I move the "if (pending_..." section up into the block
> where WL_LATCH_SET has arrived (instead of testing those variables
> every time through the loop), a couple of tests leave zombie
> (unreaped) processes behind, indicating that something funky happened
> to the state machine that I haven't yet grokked.  Will look more next
> week.

Duh.  The reason for that was the pre-existing special case for
PM_WAIT_DEAD_END, which used a sleep(100ms) loop to wait for children
to exit, which I needed to change to a latch wait.  Fixed in the next
iteration, attached.

The reason for the existing sleep-based approach was that we didn't
want to accept any more connections (or spin furiously because the
listen queue was non-empty).  So in this version I invented a way to
suppress socket events temporarily with WL_SOCKET_IGNORE, and then
reactivate them after crash reinit.

Still WIP, but I hope travelling in the right direction.

Commits

  1. Remove unneeded volatile qualifiers from postmaster.c.

  2. Fix WaitEventSetWait() buffer overrun.

  3. Refactor DetermineSleepTime() to use milliseconds.

  4. Use WaitEventSet API for postmaster's event loop.

  5. Allow parent's WaitEventSets to be freed after fork().

  6. Don't leak a signalfd when using latches in the postmaster.

  7. Add WL_SOCKET_ACCEPT event to WaitEventSet API.

  8. From: Phil Thompson <phil@river-bank.demon.co.uk>