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From: Aniko Belim <[email protected]>
To: Justin Pryzby <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: Partitioned table - scans through every partitions
Date: Fri, 25 Aug 2017 16:08:19 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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Thank you, Justin!  

Aniko




On 8/25/17, 10:44 AM, "Justin Pryzby" <[email protected]> wrote:

>On Fri, Aug 25, 2017 at 03:36:29PM +0000, Aniko Belim wrote:
>> Hi,
>> 
>> We have an issue with one of our partitioned tables. It has a column with timestamp without time zone type, and we had to partition it daily. To do that, we created the following constraints like this example:
>> CHECK (to_char(impression_time, 'YYYYMMDD'::text) = '20170202'::text)
>> 
>> 
>> The problem we’re facing is no matter how we’re trying to select from it, it scans through every partitions.
>
>
>> It scans through every partitions. Shouldn’t it only scan the dfp_in_network_impressions.dfp_in_network_impressions_20170202 child table? Or we missing something?
>> Any advice/help would highly appreciated.
>
>https://www.postgresql.org/docs/9.6/static/ddl-partitioning.html#DDL-PARTITIONING-CAVEATS
>|The following caveats apply to constraint exclusion:
>|    Constraint exclusion only works when the query's WHERE clause contains
>|    constants (or externally supplied parameters). For example, a comparison
>|    against a non-immutable function such as CURRENT_TIMESTAMP cannot be
>|    optimized, since the planner cannot know which partition the function value
>|    might fall into at run time.
>
>...

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