From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
Cc: | pgsql-bugs(at)postgresql(dot)org |
Subject: | Re: BUG #5157: Hash index not concurrency safe |
Date: | 2009-11-01 18:08:29 |
Message-ID: | 23029.1257098909@sss.pgh.pa.us |
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Lists: | pgsql-bugs |
I wrote:
> Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
>> Hash index is not concurrency safe, starting in REL8_4_0 and up to HEAD.
> Ouch. This used to be okay, because adding new entries to a hash page
> always added them at the end. The 8.4 changes to keep individual hash
> pages sorted by hashcode broke it :-(.
Actually, now that I am looking at it, that patch COMPLETELY destroyed
hash indexes. The search logic requires that index entries within a
page are ordered by hash value. Although the insertion code preserves
that property, neither _hash_splitbucket nor _hash_squeezebucket make
any attempt to do so. So it's not just a transient concurrency issue,
you can easily get corruption of a hash index leading to permanent
search failures.
Ugh. Mea culpa for letting this one through.
regards, tom lane
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