Re: Index Skip Scan - Mailing list pgsql-hackers

From Dmitry Dolgov
Subject Re: Index Skip Scan
Date
Msg-id CA+q6zcX-8KTkkpydVAKDryGU9MZhP-nW3U-cj2AS9r4_69wBrA@mail.gmail.com
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In response to Re: Index Skip Scan  (Floris Van Nee <florisvannee@Optiver.com>)
List pgsql-hackers
> On Wed, Jul 10, 2019 at 5:00 PM Floris Van Nee <florisvannee@optiver.com> wrote:
>
>
> > Thanks for testing! Could you provide a test case to show what exactly is the
> > problem?
>
> Note that in the case of a regular non-skip scan, this cursor backwards works
> because the Unique node on top does not support backwards scanning at all.
> Therefore, when creating the cursor, the actual plan actually contains a
> Materialize node on top of the Unique+Index Scan nodes. The 'fetch backwards'
> never reaches the the index scan therefore, as it just fetches stuff from the
> materialize node.

Yeah, I'm aware. The last time when I was busy with cursors I've managed to
make it work as I wanted, so at that time I decided to keep it like that, even
though without skip scan it wasn't doing backwards.



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