Re: segfault in hot standby for hash indexes

On Thu, Mar 23, 2017 at 8:43 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Wed, Mar 22, 2017 at 3:39 PM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
>> Hi,
>>
>> On Wed, Mar 22, 2017 at 8:41 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)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.
>
>

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,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com