On Thu, Oct 20, 2016 at 12:30 PM, Pavan Deolasee
<pavan.deolasee@gmail.com> wrote:
>
>
> On Thu, Oct 20, 2016 at 8:44 PM, Petr Jelinek <petr@2ndquadrant.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.