Date: Mon, 11 Feb 2019 20:36:14 -0600
From: Justin Pryzby <pryzby@telsasoft.com>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Sergei Kornilov <sk@zsrv.org>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: Re: pg11.1: dsa_area could not attach to segment
Message-ID: <20190212023614.GB31721@telsasoft.com>
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On Mon, Feb 11, 2019 at 08:14:28PM -0600, Justin Pryzby wrote:
> > Can we please see the stderr output of dsa_dump(area), added just
> > before the PANIC?  Can we see the value of "handle" when the error is
> > raised, and the directory listing for /dev/shm (assuming Linux) after
> > the crash (maybe you need restart_after_crash = off to prevent
> > automatic cleanup)?
> 
> PANIC:  dsa_area could not attach to segment index:8 handle:1076305344
> 
> I think it needs to be:
> 
> |               if (segment == NULL) {
> |                       LWLockRelease(DSA_AREA_LOCK(area));
> |                       dsa_dump(area);
> |                       elog(PANIC, "dsa_area could not attach to segment index:%zd handle:%d", index, handle);
> |               }
> 
> ..but that triggers recursion:

Here's my dsa_log (which is repeated many times and 400kB total)..

dsa_area handle 0:
  max_total_segment_size: 18446744073709551615
  total_segment_size: 15740928
  refcnt: 2
  pinned: f
  segment bins:
    segment bin 0 (at least -2147483648 contiguous pages free):
      segment index 2, usable_pages = 256, contiguous_pages = 0, mapped at 0x7f56ff9d5000
      segment index 0, usable_pages = 0, contiguous_pages = 0, mapped at 0x7f56ffbd6840
    segment bin 3 (at least 4 contiguous pages free):
      segment index 7, usable_pages = 510, contiguous_pages = 6, mapped at 0x7f56ff0b4000
      segment index 6, usable_pages = 510, contiguous_pages = 6, mapped at 0x7f56ff2b4000
      segment index 5, usable_pages = 510, contiguous_pages = 5, mapped at 0x7f56ff4b4000
      segment index 4, usable_pages = 510, contiguous_pages = 5, mapped at 0x7f56ff6b4000
      segment index 3, usable_pages = 255, contiguous_pages = 6, mapped at 0x7f56ff8b4000
      segment index 1, usable_pages = 255, contiguous_pages = 6, mapped at 0x7f56ffad6000
    segment bin 10 (at least 512 contiguous pages free):

Note negative pages.  Let me know if you want more of it (span descriptors?)

Justin