Re: postgresql 10.1 wrong plan in when using partitions bug

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От Mariel Cherkassky
Тема Re: postgresql 10.1 wrong plan in when using partitions bug
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Msg-id CA+t6e1mt-fkvZZX5Wx8B1oPrw=DQOZGr3s=xU_ZhEhKEJtJ-Og@mail.gmail.com
обсуждение исходный текст
Ответ на Re: postgresql 10.1 wrong plan in when using partitions bug  (Tomas Vondra <tomas.vondra@2ndquadrant.com>)
Ответы Re: postgresql 10.1 wrong plan in when using partitions bug
Re: postgresql 10.1 wrong plan in when using partitions bug
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Mybe I wasnt clear. I'm having a 2 layers patitions mechanism : 
My main table is called log_full : 
CREATE TABLE log_full (a text,b text,c text, start_stop text, end_Date date) partition range by (end_date))

Every day I create a partition that represent data from that day : 
create table log_full_04_02_2018 partition of radius_log_full(end_date) for VALUES from ('04-02-2018 00:00:00') TO ('05-02-2018 00:00:00') partition by list (start_stop) ;

The partition that represent the current day consist of 8 paritions on column start_stop that look like that : 
create table log_full_04_02_2018_action_status partition of log_full_04_02_2018 for VALUES in ('Start','Stop');

ALTER TABLE ONLY log_full_04_02_2018_action_status
    ADD CONSTRAINT log_full_04_02_2018_action_status_pkey PRIMARY KEY (a, b, c);

I checked the plan of the next query : 
explain select count(*) from log_full where end_date between to_date('2017/12/03','YY/MM/DD') and to_date('2017/12/03','YY/MM/DD');

and the result if full scan on all partitions.

Why it decided to run a full table scan on all partitions ?

2018-02-04 14:03 GMT+02:00 Tomas Vondra <tomas.vondra@2ndquadrant.com>:


On 02/04/2018 11:14 AM, Mariel Cherkassky wrote:
>
> Hi,
> I configured range partitions on a date column of my main
> table(log_full). Each partition represents a day in the month. Every day
> partition has a list parition of 4 tables on a text column.
>
> log_full
>           log_full_01_11_2017  -->
>                                           log_full _01_11_2017_x1
>                                           log_full _01_11_2017_x2
>                                           log_full _01_11_2017_x3 
>                                           log_full _01_11_2017_x4 
>             log_full_02_11_2017
>                                           log_full _02_11_2017_x1 
>                                           log_full _02_11_2017_x2 
>                                           log_full _02_11_2017_x3 
>                                           log_full _02_11_2017_x4
>
> and so on....
>       
>
> The date column consist of date in the next format : YYYY-MM-DD HH:24:SS
> for example : 2017-11-01 00:01:40
>
> I wanted to check the plan that I'm getting for a query that is using
> the date column and it seems that the planner choose to do seq scans on
> all tables.
>
> -Each partition consist from 15M rows.
> I have about 120 partitions.
>
> The query : 
> explain select count(*) from log_full where end_date between
> to_date('2017/12/03','YY/MM/DD') and to_date('2017/12/03','YY/MM/DD');
>
> The output is too long but it do full scans on all paritions...
> any idea what can be the problem? Is it connected to the date format ?
>

You haven't shown us how the partitions are defined, nor the query plan.
So it's rather hard to say. You mentioned text format, but then you use
to_date() to query the partitioned table. Which I guess might be the
cause, but it's hard to say for sure.

regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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