Date: Tue, 22 May 2018 13:23:07 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: pavan95 <pavan.postgresdba@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Help me in reducing the CPU cost for the high cost query below,
 as it is hitting production seriously!!
Message-ID: <20180522182307.GA9330@telsasoft.com>
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On Tue, May 22, 2018 at 03:51:44AM -0700, pavan95 wrote:
> Please find the output of explain(analyze,buffers) for the whole query in
> the below link.

> Seq Scan on res_users users (cost=750.92..1,836.69 rows=249 width=15) (actual time=3.962..17.544 rows=67 loops=1) 

Not sure but would you try creating an index on:
res_users.res_employee_id

> Seq Scan on res_users user1 (cost=0.00..58.03 rows=1,303 width=15) (actual time=0.002..0.002 rows=1 loops=1)

Also the planner's estimate for table:res_users is off by 1300x..so you should
probably vacuum analyze it then recheck.  I don't think we know what version
postgres you have, but last week's patch releases include a fix which may be
relevant (reltuples including dead tuples).

Also I don't know the definition of this table or its indices:
tms_workflow_history

..but it looks like an additional or modified index or maybe clustering the
table on existing index might help (active? is_final_approver?)
Or maybe this should be 3 separate indices rather than composite index?
Perhaps some of those could be BRIN indices, depending on postgres version

Justin