Re: gist vacuum gist access

On Mon, Sep 8, 2014 at 12:51 PM, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com
> wrote:

> On 09/08/2014 11:19 AM, Alexander Korotkov wrote:
>
>> On Mon, Sep 8, 2014 at 12:08 PM, Alexander Korotkov <aekorotkov(at)gmail(dot)com
>> >
>> wrote:
>>
>> On Mon, Sep 8, 2014 at 11:13 AM, Heikki Linnakangas <
>>> hlinnakangas(at)vmware(dot)com> wrote:
>>>
>>> In the b-tree code, we solved that problem back in 2006, so it can be
>>>> done but requires a bit more code. In b-tree, we solved it with a
>>>> "vacuum
>>>> cycle ID" number that's set on the page halves when a page is split.
>>>> That
>>>> allows VACUUM to identify pages that have been split concurrently sees
>>>> them, and "jump back" to vacuum them too. See commit
>>>> http://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=
>>>> 5749f6ef0cc1c67ef9c9ad2108b3d97b82555c80. It should be possible to do
>>>> something similar in GiST, and in fact you might be able to reuse the
>>>> NSN
>>>> field that's already set on the page halves on split, instead of adding
>>>> a
>>>> new "vacuum cycle ID".
>>>>
>>> ...
>>>
>>
>> Another note. Assuming we have NSN which can play the role of "vacuum
>> cycle
>> ID", can we implement sequential (with possible "jump back") index scan
>> for
>> GiST?
>>
>
> Yeah, I think it would work. It's pretty straightforward, the page split
> code already sets the NSN, just when we need it. Vacuum needs to memorize
> the current NSN when it begins, and whenever it sees a page with a higher
> NSN (or the FOLLOW_RIGHT flag is set), follow the right-link if it points
> to lower-numbered page.

I mean "full index scan" feature for SELECT queries might be implemented as
well as sequential VACUUM.

------
With best regards,
Alexander Korotkov.