Horton

Re: "could not reattach to shared memory" on buildfarm member dory

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Noah Misch <noah@leadboat.com>, Heath Lord <heath.lord@crunchydata.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Stephen Frost <sfrost@snowman.net>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-05-01T00:24:19Z
Lists: pgsql-hackers 
Him

On 2018-04-30 20:01:40 -0400, Tom Lane wrote:
> What seems like a plausible theory at this point is that the apparent
> asynchronicity is due to the allocation being triggered by a different
> thread, and the fact that our added monitoring code seems to make the
> failure more likely can be explained by that code changing the timing.
> But what thread could it be?  It doesn't really look to me like either
> the signal thread or the timer thread could eat 4MB.

It seems plausible that the underlying allocator allocates larger chunks
to serve small allocations.  But we don't seem to have started any threads
at PGSharedMemoryReAttach() time? So it'd have to be something else that
starts threads.

Heath, could you use process explorer or such to check which processes
are running inside a working backend process?

Greetings,

Andres Freund

Commits

  1. Avoid "could not reattach" by providing space for concurrent allocation.

  2. Assert that pgwin32_signal_initialize() has been called early enough.

  3. Remove investigative code for can't-reattach-to-shared-memory errors.

  4. Does it help to wait before reattaching?

  5. Map and unmap the shared memory block before risking VirtualFree.

  6. Further effort at preventing memory map dump from affecting the results.

  7. Remove Windows module-list-dumping code.

  8. Dump full memory maps around failing Windows reattach code.

  9. Get still more info about Windows can't-reattach-to-shared-memory errors.

  10. Get more info about Windows can't-reattach-to-shared-memory errors.

  11. Try to get some info about Windows can't-reattach-to-shared-memory errors.