Subject: Re: FW: Re: Query is running very slow......
To: Dinesh Chandra 12108 <Dinesh.Chandra@cyient.com>
Cc: "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
References: <3152be5a435f45649cef6bf9321beb9a@cyient.com>
 <4caed7cc-07d8-e364-78ca-7a96b9780a9d@2ndquadrant.com>
 <39b30cfde27a48898340a69940581727@cyient.com>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <acba2082-c299-e712-4964-29c47f839a57@2ndquadrant.com>
Date: Thu, 25 May 2017 17:38:13 +0200
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On 5/25/17 2:26 PM, Dinesh Chandra 12108 wrote:
> Hi Tomas,
> 
> Please find the below input for slow query.
> 
> (a) something about the hardware it's running on
>   RAM-->64 GB, CPU->40core
> 
> (b) amounts of data in the tables / databases
> Database size 	:32GB
> -----------------
> Tables size
> -----------------
> Workflow.project		: 8194 byte
> workflow.tool_performance	:175 MB
> workflow.evidence_to_do	:580 MB
> 
> (c) EXPLAIN or even better EXPLAIN ANALYZE of the query
> 
> "GroupAggregate  (cost=16583736169.63..18157894828.18 rows=5920110 width=69)"
> "  ->  Sort  (cost=16583736169.63..16714893857.43 rows=52463075120 width=69)"
> "        Sort Key: tool_performance.project_id, project.project_name, tool_performance.step_id, (date_trunc('day'::text, tool_performance.insert_time)), tool_performance.user_id"
> "        ->  Nested Loop  (cost=2.42..787115179.07 rows=52463075120 width=69)"
> "              ->  Seq Scan on evidence_to_do  (cost=0.00..119443.95 rows=558296 width=0)"
> "                    Filter: (status_id = ANY ('{15100,15150,15200,15300,15400,15500}'::bigint[]))"
> "              ->  Materialize  (cost=2.42..49843.24 rows=93970 width=69)"
> "                    ->  Hash Join  (cost=2.42..49373.39 rows=93970 width=69)"
> "                          Hash Cond: (tool_performance.project_id = project.project_id)"
> "                          ->  Seq Scan on tool_performance  (cost=0.00..48078.88 rows=93970 width=39)"
> "                                Filter: ((insert_time > '2017-05-01 00:00:00+05:30'::timestamp with time zone) AND (insert_time < '2017-05-02 00:00:00+05:30'::timestamp with time zone))"
> "                          ->  Hash  (cost=1.63..1.63 rows=63 width=38)"
> "                                ->  Seq Scan on project  (cost=0.00..1.63 rows=63 width=38)"
> 

Are you sure this is the same query? The query you posted includes there 
two join conditions:

     evidence_to_do.project_id = tool_performance.project_id
     evidence_to_do.project_id = project.project_id

But the plan only seems to enforce the equality between 'project' and 
'tool_performance'. So when joining the evidence_to_do, it performs a 
cartesian product, producing ~52B rows (estimated). That can't be fast.

regards

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


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