From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
Cc: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Parallel Bitmap scans a bit broken |
Date: | 2017-03-09 17:17:09 |
Message-ID: | CA+TgmoYTHt7WUio2Kx+qbR1Uk3ufcMsvejMCDx7WB90Gf4DjDw@mail.gmail.com |
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On Thu, Mar 9, 2017 at 11:50 AM, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> On Thu, Mar 9, 2017 at 10:02 PM, Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
>> I slightly modified your query to reproduce this issue.
>>
>> explain analyze select * from r1 where value<555;
>>
>> Patch is attached to fix the problem.
>
> I forgot to mention the cause of the problem.
>
> if (istate->schunkptr < istate->nchunks)
> {
> PagetableEntry *chunk = &ptbase[idxchunks[istate->schunkptr]];
> PagetableEntry *page = &ptbase[idxpages[istate->spageptr]];
> BlockNumber chunk_blockno;
>
> In above if condition we have only checked istate->schunkptr <
> istate->nchunks that means we have some chunk left so we are safe to
> access idxchunks, But just after that we are accessing
> ptbase[idxpages[istate->spageptr]] without checking that accessing
> idxpages is safe or not.
>
> tbm_iterator already handling this case, I broke it in tbm_shared_iterator.
I don't know if this is the only problem -- it would be good if David
could retest -- but it's certainly *a* problem, so committed.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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