Re: Parallel Bitmap scans a bit broken

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.

--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com