Subject: Re: Queries are taking way longer in 9.6 than 9.5
To: Ravi Tammineni <rtammineni@partner.aligntech.com>,
 Chris Mair <chris@1006.org>
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Cc: "pgsql-general@postgresql.org" <pgsql-general@postgresql.org>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <70190c66-cf64-4741-1cd7-a6cf08f4101f@2ndquadrant.com>
Date: Tue, 17 Jan 2017 23:21:15 +0100
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Hi,

after looking at the explain plans again, I very much doubt those come 
from the same query. The reason is the 9.5 plan contains this part:

     ->  HashAggregate  (cost=67.54..68.12 rows=192 width=4)
           Group Key: d.vip_patient_id
           ->  Nested Loop  (cost=0.17..67.44 rows=192 width=4)
                 ->  Index Scan using unq_user_name on tblcnaccounts ...
                       Index Cond: ((user_name)::text = 'dddddd'::text)
                 ->  Index Only Scan using idx_tblcndoctorpatientmap ...
                       Index Cond: (master_user_id = a.master_user_id)

while the 9.6 plan does not include anything like that, i.e. there's 
only a single aggregate at the top level, without any group keys. Also, 
the SQL query you've provided does not include any GROUP BY clause, so I 
claim that those plans are from two different queries.

regards
Tomas

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


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