From: Jesper Pedersen <jesper.pedersen@redhat.com>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: Bhushan Uparkar <bhushan.uparkar@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Cc: Alexander Korotkov <a.korotkov@postgrespro.ru>
Subject: Re: Index Skip Scan
Date: Fri, 17 Aug 2018 13:15:46 -0400
Message-ID: <9f2a0339-7d4a-e632-2ad6-237b24a95fa6@redhat.com> (raw)
In-Reply-To: <CAH2-WznxAN940e=2D8Auz06d=_ZK6F5LVH0HUMbCXGAa=Tirpw@mail.gmail.com>
References: <707b6f68-16fa-7aa7-96e5-eeb4865e6a30@redhat.com>
<CAPpHfducUiDw7hVT=Vui8rxTmawCkVc0H--v=jdbztMUGhzuRg@mail.gmail.com>
<89F84E17-D684-4717-B66F-0F05CB00168E@gmail.com>
<CAEepm=1ikXHVgSNruQ1HydDZm3OLnLNb5qT2c8S=Mh-VsFQXcQ@mail.gmail.com>
<CAH2-WznxAN940e=2D8Auz06d=_ZK6F5LVH0HUMbCXGAa=Tirpw@mail.gmail.com>
Hi Peter,
On 08/16/2018 03:48 PM, Peter Geoghegan wrote:
> On Wed, Aug 15, 2018 at 11:22 PM, Thomas Munro
> <thomas.munro@enterprisedb.com> wrote:
>> * groups and certain aggregates (MIN() and MAX() of suffix index
>> columns within each group)
>> * index scans where the scan key doesn't include the leading columns
>> (but you expect there to be sufficiently few values)
>> * merge joins (possibly the trickiest and maybe out of range)
>
> FWIW, I suspect that we're going to have the biggest problems in the
> optimizer. It's not as if ndistinct is in any way reliable. That may
> matter more on average than it has with other path types.
>
Thanks for sharing this; it is very useful to know.
Best regards,
Jesper
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: jesper.pedersen@redhat.com, pg@bowt.ie, thomas.munro@enterprisedb.com, bhushan.uparkar@gmail.com, a.korotkov@postgrespro.ru
Subject: Re: Index Skip Scan
In-Reply-To: <9f2a0339-7d4a-e632-2ad6-237b24a95fa6@redhat.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox