Thread: sinval.c / sinvaladt.c restructuring
I just modified the interactions in sinval.c and sinvaladt.c per http://thread.gmane.org/gmane.comp.db.postgresql.devel.patches/18820/focus=18822 It looks a lot saner this way: the code that actually deals with the queue, including locking etc, is all in sinvaladt.c. This means that the struct definition of the queue, and the queue pointer, are now internal "implementation details" inside sinvaladt.c. One side effect of this change is that the call to SendPostmasterSignal now occurs after the lock has been released. ISTM this is a good idea on general principles (no syscalls in lwlocked code), but I'm wondering if I created a thundering hoard problem that did not exist before. All tests pass. As a test of Review Board, I uploaded the patch to it: http://reviewdemo.postgresql.org/r/19/ -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
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Alvaro Herrera wrote:
> I just modified the interactions in sinval.c and sinvaladt.c per
> http://thread.gmane.org/gmane.comp.db.postgresql.devel.patches/18820/focus=18822
>
> It looks a lot saner this way: the code that actually deals with the
> queue, including locking etc, is all in sinvaladt.c. This means that
> the struct definition of the queue, and the queue pointer, are now
> internal "implementation details" inside sinvaladt.c.
>
> One side effect of this change is that the call to SendPostmasterSignal
> now occurs after the lock has been released. ISTM this is a good idea
> on general principles (no syscalls in lwlocked code), but I'm wondering
> if I created a thundering hoard problem that did not exist before.
>
> All tests pass.
>
> As a test of Review Board, I uploaded the patch to it:
> http://reviewdemo.postgresql.org/r/19/
>
> --
> Alvaro Herrera http://www.CommandPrompt.com/
> The PostgreSQL Company - Command Prompt, Inc.
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--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://postgres.enterprisedb.com
+ If your life is a hard drive, Christ can be your backup. +
Alvaro Herrera <alvherre@commandprompt.com> writes:
> One side effect of this change is that the call to SendPostmasterSignal
> now occurs after the lock has been released. ISTM this is a good idea
> on general principles (no syscalls in lwlocked code), but I'm wondering
> if I created a thundering hoard problem that did not exist before.
Forgot to reply to this earlier, but I think this is OK. The test for
setting signal_postmaster is for exact equality of numMsgs to a
threshold, so at least in simple cases only one backend will send the
signal. You could imagine scenarios where the slowest backend is trying
to catch up and numMsgs oscillates around the threshold, but it seems
unlikely to be a problem in practice. I concur that moving the signal
out of the locked code is a good thing. (Maybe move the elog(DEBUG4)
as well?)
regards, tom lane