Reply-To: jesper.pedersen@redhat.com
Subject: Re: Index Skip Scan
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: pgsql-hackers@lists.postgresql.org, Thomas Munro <munro@ip9.org>
References: <707b6f68-16fa-7aa7-96e5-eeb4865e6a30@redhat.com>
 <CA+q6zcXdP=PCaVRx3OgpyKK+NgNfrnnSA66rkvxRLeZrkYjEaA@mail.gmail.com>
 <153909254478.1479.11809244127214809171.pgcf@coridan.postgresql.org>
From: Jesper Pedersen <jesper.pedersen@redhat.com>
Organization: Red Hat
Message-ID: <b0949c46-ec77-4b82-48fe-916cd5c12fd1@redhat.com>
Date: Tue, 9 Oct 2018 09:58:09 -0400
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Hi Pavel,

On 10/9/18 9:42 AM, Pavel Stehule wrote:
> I tested last patch and I have some notes:
> 
> 1.
> 
> postgres=# explain select distinct a10000 from foo;
> +-------------------------------------------------------------------------------------------+
> |                                        QUERY PLAN                                         |
> +-------------------------------------------------------------------------------------------+
> | Unique  (cost=0.43..4367.56 rows=9983 width=4)                                            |
> |   ->  Index Skip Scan using foo_a10000_idx on foo  (cost=0.43..4342.60 rows=9983 width=4) |
> +-------------------------------------------------------------------------------------------+
> (2 rows)
> 
> In this case Unique node is useless and can be removed
> 
> 2. Can be nice COUNT(DISTINCT support) similarly like MIN, MAX suppport
> 
> 3. Once time patched postgres crashed, but I am not able to reproduce it.
>

Please, send that query through if you can replicate it. The patch 
currently passes an assert'ed check-world, so your query clearly 
triggered something that isn't covered yet.

> Looks like very interesting patch, and important for some BI platforms
> 

Thanks for your review !

Best regards,
  Jesper