Re: Microvacuum support for Hash Index

On Fri, Mar 17, 2017 at 8:20 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Thu, Mar 16, 2017 at 9:39 PM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
>>>>
>>>
>>> Don't you think, we should also clear it during the replay of
>>> XLOG_HASH_DELETE? We might want to log the clear of flag along with
>>> WAL record for XLOG_HASH_DELETE.
>>>
>>
>> Yes, it should be cleared. I completely missed this part in a hurry.
>> Thanks for informing. I have taken care of it in the attached v2
>> patch.
>>
>
> + /*
> + * Mark the page as not containing any LP_DEAD items. See comments
> + * in hashbucketcleanup() for details.
> + */
> + pageopaque = (HashPageOpaque) PageGetSpecialPointer(page);
> + pageopaque->hasho_flag &= ~LH_PAGE_HAS_DEAD_TUPLES;
>
> Your comment here says, refer hashbucketcleanup and in that function,
> the comment says "Clearing this flag is just a hint; replay won't redo
> this.". Both seems contradictory. You need to change the comment in
> hashbucketcleanup.

Done. Please check the attached v3 patch.

As I said in my previous e-mail, I think you need
> to record clearing of this flag in WAL record XLOG_HASH_DELETE as you
> are not doing this unconditionally and then during replay clear it
> only when the WAL record indicates the same.

Thank you so much for putting that point. I too think that we should
record the flag status in the WAL record and clear it only when
required during replay.

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