From: | "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> |
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To: | "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | "ykhuang" <hyk(at)ruc(dot)edu(dot)cn>, <pgsql-bugs(at)postgresql(dot)org> |
Subject: | Re: Error during hash index scans can cause postgres halt! |
Date: | 2008-03-07 15:25:08 |
Message-ID: | 47D15E54.6020706@enterprisedb.com |
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Lists: | pgsql-bugs |
Tom Lane wrote:
> "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com> writes:
>> I can reproduce this, with --enable-cassert. It crashes when aborting
>> the transaction, in ReleaseResources_hash. The HashScanList items are
>> allocated in ExecutorState memory context, but that context has already
>> been deleted by the time we get to ReleaseResources_hash.
>
> Ouch. So this has been broken (by me, I think :-() since 8.0. Tells
> you something about how many people use hash indexes :-(
Yeah. Also, this is very hard to trigger without --enable-cassert (or
just CLOBBER_FREED_MEMORY). It's extremely unlikely that something new
is allocated on the piece of memory that was used by an HashScanList
item, during AbortTransaction processing.
ykhuang, were you running an assertion-enabled build as well?
>> Another idea would be to allocate the HashScanList items in a
>> longer-lived memory context. The IndexScanDesc struct pointed to by the
>> HashScanList would still be in ExecutorState context, but that's all
>> right because we don't need to access it in ReleaseResources_hash.
>
> That seems like a winner to me. We can rely on the resource owner
> mechanism to free up individual HashScanList items, so there's no real
> need to keep them in a short-lived context. I'm inclined to just drop
> them into TopMemoryContext. We could make a hash-specific context but
> I'm not convinced it's worth the extra code to do it.
Want me to hack up a patch, or you going to just commit that yourself?
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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