Re: Page Scan Mode in Hash Index

On Wed, Sep 20, 2017 at 4:56 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Wed, Sep 20, 2017 at 7:19 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>>> Page-at-a-time index vacuum as in _hash_vacuum_one_page doesn't matter
>>> because such an operation doesn't allow TIDs to be reused.
>>
>> Page-at-a-time index vacuum also allows TIDs to be reused but this is
>> done only for already marked dead items whereas vacuum can make the
>> non-dead entries to be removed.  We don't have a problem with
>> page-at-a-time vacuum as it won't remove any items which the scan is
>> going to mark as dead.
>
> I don't think page-at-a-time index vacuum allows heap TIDs to be
> reused.
>

Right, I was thinking from the perspective of the index entry.  Before
marking index entry as dead, we do check for heaptid.  So, as heaptid
can't be reused via Page-at-a-time index vacuum, scan won't mark index
entry as dead.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com