Re: [HACKERS] segfault in hot standby for hash indexes

On Thu, Mar 23, 2017 at 9:17 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Thu, Mar 23, 2017 at 8:43 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> > On Wed, Mar 22, 2017 at 3:39 PM, Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
> >> Hi,
> >>
> >> On Wed, Mar 22, 2017 at 8:41 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> >>
> >> To fix this, I think we should pass 'REGBUF_KEEP_DATA' while
> >> registering the buffer. Something like this,
> >>
> >> -                       XLogRegisterBuffer(0, buf, REGBUF_STANDARD);
> >> +                       XLogRegisterBuffer(0, buf, REGBUF_STANDARD |
> >> REGBUF_KEEP_DATA);
> >>
> >> Attached is the patch that fixes this issue.
> >>
> >
> > I think this will work, but not sure if there is a merit to deviate
> > from what btree does to handle this case.   One thing I find slightly
> > awkward in hash_xlog_vacuum_get_latestRemovedXid() is that you are
> > using a number of tuples registered as part of fixed data
> > (xl_hash_vacuum_one_page) to traverse the data registered as buf data.
> > I think it will be better if we register offsets also in fixed part of
> > data as we are doing btree case.

Agreed. I have made the changes accordingly. Please check attached v2 patch.

>
> >
> >
>
> Also another small point in this regard, do we need two separate
> variables to track number of deleted items in below code?  I think one
> variable is sufficient.
>
> _hash_vacuum_one_page()
> {
> ..
> deletable[ndeletable++] = offnum;
> tuples_removed += 1;--
With Regards,
Ashutosh Sharma
EnterpriseDB:http://www.enterprisedb.com
> ..
> }
>

Yes, I think 'ndeletable' alone should be fine.

--
With Regards,
Ashutosh Sharma
EnterpriseDB:http://www.enterprisedb.com

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