Re: Microvacuum support for Hash Index

On Thu, Mar 16, 2017 at 11:11 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Wed, Mar 15, 2017 at 9:23 PM, Ashutosh Sharma <ashu.coek88@gmail.com> wrote:
>>
>>>
>>> Few other comments:
>>> 1.
>>> + if (ndeletable > 0)
>>> + {
>>> + /* No ereport(ERROR) until changes are logged */
>>> + START_CRIT_SECTION();
>>> +
>>> + PageIndexMultiDelete(page, deletable, ndeletable);
>>> +
>>> + pageopaque = (HashPageOpaque) PageGetSpecialPointer(page);
>>> + pageopaque->hasho_flag &= ~LH_PAGE_HAS_DEAD_TUPLES;
>>>
>>> You clearing this flag while logging the action, but same is not taken
>>> care during replay. Any reasons?
>>
>> That's because we  conditionally WAL Log this flag status and when we
>> do so, we take a it's FPI.
>>
>
> Sure, but we are not clearing in conditionally.  I am not sure, how
> after recovery it will be cleared it gets set during normal operation.
> Moreover, btree already clears similar flag during replay (refer
> btree_xlog_delete).

You were right. In case datachecksum is enabled or wal_log_hint is set
to true, 'LH_PAGE_HAS_DEAD_TUPLES' will get wal logged and therefore
needs to be cleared on the standby as well. Attached is the patch that
clears this flag on standby during replay.

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