Horton

Re: EINTR in ftruncate()

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>, Thomas Munro <thomas.munro@gmail.com>
Cc: Pg Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-07-06T00:20:15Z
Lists: pgsql-hackers 
Hi,

On 2022-07-04 13:07:50 +0200, Alvaro Herrera wrote:
> On 2022-Jul-01, Andres Freund wrote:
> 
> > On 2022-07-01 19:55:16 +0200, Alvaro Herrera wrote:
> > > On 2022-Jul-01, Andres Freund wrote:
> 
> > > > 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:
> 
> > That whole approach seems quite wrong to me. At the absolute very least the
> > code needs to check if interrupts are being processed in the current context
> > before just giving up due to ProcDiePending || QueryCancelPending.
> 
> For the time being, I can just push the addition of the EINTR retry
> without testing ProcDiePending || QueryCancelPending.

I think we'd be better off disabling at least some signals during
dsm_impl_posix_resize(). I'm afraid we'll otherwise just find another
variation of these problems. I haven't checked the source of ftruncate, but
what Thomas dug up for fallocate makes it pretty clear that our current
approach of just retrying again and again isn't good enough. It's a bit more
obvious that it's a problem for fallocate, but I don't think it's worth having
different solutions for the two.

Greetings,

Andres Freund

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.