Re: [WIP PATCH] Index scan offset optimisation using visibility map - Mailing list pgsql-hackers

Hello.

> Okay, it has been more than a couple of days and the patch has not been

> updated, so I am marking as returned with feedback. 

Yes, it is more than couple of days passed, but also there is almost no feedback since 20 Mar after patch design was changed :)

But seriously - I still working on it and was digging into just last night ( https://github.com/michail-nikolaev/postgres/commits/index_only_fetch )

The main issue currently is a cost estimation. In right case (10m relation, 0.5 index correlation, 0.1 selectivity for filter) - it works like a charm with 200%-400% performance boost.

But the same case with 1.0 selectivity gives 96% comparing to baseline. So, to do correct cost estimation I need correct selectivity of filter predicate.

Currently I am thinking to calculate it on fly - and switch to the new method if selectivity is small. But it feels a little akward.

Thanks,

Michail.