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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: vjoshi@zetainteractive.com, Jim Nasby <Jim.Nasby@bluetreble.com>
To: Scott Marlowe <scott.marlowe@gmail.com>
To: Varadharajan Mukundan <srinathsmn@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Performance issues
Date: Tue, 17 Mar 2015 12:42:06 +0100
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Hi,

On 17.3.2015 08:41, Vivekanand Joshi wrote:
> Hi Guys,
> 
> Next level of query is following:
> 
> If this works, I guess 90% of the problem will be solved.
> 
> SELECT
>                     COUNT(DISTINCT TARGET_ID)
>                 FROM
>                     S_V_F_PROMOTION_HISTORY_EMAIL PH
>                     INNER JOIN S_V_D_CAMPAIGN_HIERARCHY CH
>                         ON PH.TOUCHPOINT_EXECUTION_ID =
> CH.TOUCHPOINT_EXECUTION_ID
>                 WHERE
>                     1=1
>                     AND SEND_DT >= '2014-03-13'
>                     AND SEND_DT <= '2015-03-14'
> 
> 
> In this query, I am joining two views which were made earlier with CTEs. I
> have replaced the CTE's with subqueries. The view were giving me output in
> around 5-10 minutes and now I am getting the same result in around 3-4
> seconds.
> 
> But when I executed the query written above, I am again stuck. I am
> attaching the query plan as well the link.
> 
> http://explain.depesz.com/s/REeu
> 
> I can see most of the time is spending inside a nested loop and total
> costs comes out be cost=338203.81..338203.82.

Most of that cost comes from this:

Seq Scan on s_f_promotion_history base (cost=0.00..283,333.66 rows=1
width=32)
  Filter: ((send_dt >= '2014-03-13 00:00:00'::timestamp without time
zone) AND (send_dt <= '2015-03-14 00:00:00'::timestamp without time


That's a bit weird, I guess. If you analyze this part of the query
separately, i.e.

EXPLAIN ANALYZE SELECT * FROM s_f_promotion_history
 WHERE (send_dt >= '2014-03-13 00:00:00')
   AND (send_dt <= '2015-03-14 00:00:00')

what do you get?

I suspect it's used in EXISTS, i.e. something like this:

... WHERE EXISTS (SELECT * FROM s_f_promotion_history
                   WHERE ... send_dt conditions ...
                     AND touchpoint_execution_id =
     s_f_touchpoint_execution_status_history_1.touchpoint_execution_id)

and this is transformed into a nested loop join. If there's a
misestimate, this may be quite expensive - try to create index on

   s_f_promotion_history (touchpoint_execution_id, send_date)


regards

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


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