Re: Surprised by index choice for count(*) - Mailing list pgsql-general

From Rob Sargent
Subject Re: Surprised by index choice for count(*)
Date
Msg-id 59632FB7-2378-4A77-8B37-BCF5A438411F@gmail.com
Whole thread Raw
In response to Re: Surprised by index choice for count(*)  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-general
Thank you both.  Simple, as expected.  And I’m easily surprised.
Version 10 (perhaps obviously) for those scoring at home.

> On May 1, 2018, at 10:11 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Rob Sargent <robjsargent@gmail.com> writes:
>> Should I be?  I would have thought the pk would have been chosen v.
>> function index?
>
> If I'm reading this correctly, the PK index contains uuids while
> the fpv index contains float4s, meaning the latter is probably half
> the size.  So scanning it is a lot cheaper, at least according to
> the planner's cost model.
>
>             regards, tom lane



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