| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
| Cc: | Petr Jelinek <petr(at)2ndquadrant(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Robert Haas <robertmhaas(at)gmail(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Indirect indexes |
| Date: | 2016-10-20 15:50:57 |
| Message-ID: | CAGTBQpZz0axwuRoNFG+1Y1gBnR_EkYzNbJoxwoWtT-a5VJttuQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Thu, Oct 20, 2016 at 12:30 PM, Pavan Deolasee
<pavan(dot)deolasee(at)gmail(dot)com> wrote:
>
>
> On Thu, Oct 20, 2016 at 8:44 PM, Petr Jelinek <petr(at)2ndquadrant(dot)com> wrote:
>>
>>
>>
>> WARM can do WARM update 50% of time, indirect index can do HOT update
>> 100% of time (provided the column is not changed), I don't see why we
>> could not have both solutions.
>>
>
> I think the reason why I restricted WARM to one update per chain, also
> applies to indirect index. For example, if a indirect column value is
> changed from 'a' to 'b' and back to 'a', there will be two pointers from 'a'
> to the PK and AFAICS that would lead to the same duplicate scan issue.
>
> We have a design to convert WARM chains back to HOT and that will increase
> the percentage of WARM updates much beyond 50%. I was waiting for feedback
> on the basic patch before putting in more efforts, but it went unnoticed
> last CF.
With indirect indexes, since you don't need to insert a tid, you can
just "insert on conflict do nothing" on the index.
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