Re: Autovacuum daemon terminated by signal 11

Tom Lane wrote:

> What is happening is that autovacuum_do_vac_analyze contains
>
> old_cxt = MemoryContextSwitchTo(AutovacMemCxt);
> ...
> vacuum(vacstmt, relids);
> ...
> MemoryContextSwitchTo(old_cxt);
>
> and at the time it is called by process_whole_db, CurrentMemoryContext
> points at TopTransactionContext. Which gets destroyed because vacuum()
> internally finishes that transaction and starts a new one. When we
> come out of vacuum(), CurrentMemoryContext again points at
> TopTransactionContext, but *its not the same one*. The closing
> MemoryContextSwitchTo is installing a stale pointer, which then remains
> active into CommitTransaction. It's a wonder this code ever works.

Hmm, in retrospect this is pretty obviously buggy. I can't say that
it's that easy for me to reproduce it though; I definitely can't make it
crash. Maybe by sheer luck, the new TopTransactionContext pointer
points to the same memory area that the old was stored in.

I think this patch should fix it. Justin, would you try it and report
back? I would commit it right away since it seems simple enough, but
since I can't reproduce the crash, I prefer external confirmation first
:-)

--
Alvaro Herrera http://www.CommandPrompt.com/
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