Horton

Re: EINTR in ftruncate()

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Andres Freund <andres@anarazel.de>
Cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-07-01T17:55:16Z
Lists: pgsql-hackers 
On 2022-Jul-01, Andres Freund wrote:

> On 2022-07-01 17:41:05 +0200, Alvaro Herrera wrote:
> > Nicola Contu reported two years ago to pgsql-general[1] that they were
> > having sporadic query failures, because EINTR is reported on some system
> > call.  I have been told that the problem persists, though it is very
> > infrequent.  I propose the attached patch.  Kyotaro proposed a slightly
> > different patch which also protects write(), but I think that's not
> > necessary.
> 
> What is the reason for the || ProcDiePending || QueryCancelPending bit? What
> if there's dsm operations intentionally done while QueryCancelPending?

That mirrors the test for the other block in that function, which was
added by 63efab4ca139, whose commit message explains:

    Allow DSM allocation to be interrupted.
    
    Chris Travers reported that the startup process can repeatedly try to
    cancel a backend that is in a posix_fallocate()/EINTR loop and cause it
    to loop forever.  Teach the retry loop to give up if an interrupt is
    pending.  Don't actually check for interrupts in that loop though,
    because a non-local exit would skip some clean-up code in the caller.

Thanks for looking!

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/

Commits

  1. Provide sigaction() for Windows.

  2. Emulate sigprocmask(), not sigsetmask(), on Windows.

  3. Make dsm_impl_posix_resize more future-proof.

  4. Don't clobber postmaster sigmask in dsm_impl_resize.

  5. Create a distinct wait event for POSIX DSM allocation.

  6. Remove redundant ftruncate() for POSIX DSM memory.

  7. Block signals while allocating DSM memory.

  8. Remove dsm_resize() and dsm_remap().

  9. XLOG (also known as WAL -:)) Bootstrap/Startup/Shutdown.