Re: [WIP PATCH] Index scan offset optimisation using visibility map

Hi, Michail!

Here are points that we need to address before advancing the patch.

> 20 февр. 2018 г., в 11:45, Andrey Borodin <x4mmm(at)yandex-team(dot)ru> написал(а):
>
> Minor spots:
> There are some trailing whitespaces at line ends
>> Offset cannot be optimized because parallel execution
> I'd replace with
>> Offset cannot be optimized [in spite of | due to] parallel execution
>

> From my point of view, you should add to patch some words here
> https://www.postgresql.org/docs/current/static/indexes-index-only-scans.html

And few thoughts about plan cost estimation. Plz check create_limit_path() logic on cost estimation. I don't think you have enough information there to guess about possibility of IoS offset computation.
> I do not know if it is possible to take into account this optimization in cost estimation.
> Does Limit node take cost of scanning into startup cost?

I'm marking patch as WoA, plz ping it to Need Review when done.

Thanks!

Best regards, Andrey Borodin.