Re: Parallel Bitmap scans a bit broken

On 10 March 2017 at 06:17, Robert Haas <robertmhaas@gmail.com> wrote:

> On Thu, Mar 9, 2017 at 11:50 AM, Dilip Kumar <dilipbalaut@gmail.com>
> wrote:
> > On Thu, Mar 9, 2017 at 10:02 PM, Dilip Kumar <dilipbalaut@gmail.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.
>

Thanks for committing, and generally parallelising more stuff.

I confirm that my test case is now working again.

I'll be in this general area today, so will mention if I stumble over
anything that looks broken.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
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