Date: Thu, 18 Sep 2014 23:01:34 +0200 (CEST)
From: "Mkrtchyan, Tigran" <tigran.mkrtchyan@desy.de>
To: Merlin Moncure <mmoncure@gmail.com>
Cc: postgres performance list <pgsql-performance@postgresql.org>
Message-ID: <234230249.45693.1411074094865.JavaMail.zimbra@desy.de>
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 <CAHyXU0xSJR=r4savNfMcpzxBh9ZzgMc4aZtD4DxramZiexkYSw@mail.gmail.com>
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Subject: Re: postgres 9.3 vs. 9.4
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----- Original Message -----
> From: "Merlin Moncure" <mmoncure@gmail.com>
> To: "Tigran Mkrtchyan" <tigran.mkrtchyan@desy.de>
> Cc: "postgres performance list" <pgsql-performance@postgresql.org>
> Sent: Thursday, September 18, 2014 10:32:20 PM
> Subject: Re: [PERFORM] postgres 9.3 vs. 9.4
> 
> On Thu, Sep 18, 2014 at 4:58 AM, Mkrtchyan, Tigran
> <tigran.mkrtchyan@desy.de> wrote:
> >
> > 9.3.5:
> >         0.035940        END;
> >
> >
> > 9.4beta2:
> >         0.957854        END;
> 
> 
> time being spent on 'END' is definitely suggesting i/o related issues.
> This is making me very skeptical that postgres is the source of the
> problem.   I also thing synchronous_commit is not set properly on the
> new instance (or possibly there is a bug or some such).  Can you
> verify via:
> 
> select * from pg_settings where name = 'synchronous_commit';
> 
> on both servers?


here you are:

9.4beta2
postgres=# select version();
                                                     version                                                     
-----------------------------------------------------------------------------------------------------------------
 PostgreSQL 9.4beta2 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4), 64-bit
(1 row)

postgres=# select * from pg_settings where name = 'synchronous_commit';
        name        | setting | unit |          category          |                      short_desc                       | extra_desc | context | vartype |       
source       | min_val | max_val |          enumvals           | boot_val | reset_val |               sourcefile                | sourceline 
--------------------+---------+------+----------------------------+-------------------------------------------------------+------------+---------+---------+-------
-------------+---------+---------+-----------------------------+----------+-----------+-----------------------------------------+------------
 synchronous_commit | off     |      | Write-Ahead Log / Settings | Sets the current transaction's synchronization level. |            | user    | enum    | config
uration file |         |         | {local,remote_write,on,off} | on       | off       | /var/lib/pgsql/9.4/data/postgresql.conf |        622
(1 row)


9.3.5
postgres=# select version();
                                                   version                                                    
--------------------------------------------------------------------------------------------------------------
 PostgreSQL 9.3.5 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4), 64-bit
(1 row)

postgres=# select * from pg_settings where name = 'synchronous_commit';
        name        | setting | unit |          category          |                      short_desc                       | extra_desc | context | vartype |       
source       | min_val | max_val |          enumvals           | boot_val | reset_val |               sourcefile                | sourceline 
--------------------+---------+------+----------------------------+-------------------------------------------------------+------------+---------+---------+-------
-------------+---------+---------+-----------------------------+----------+-----------+-----------------------------------------+------------
 synchronous_commit | off     |      | Write-Ahead Log / Settings | Sets the current transaction's synchronization level. |            | user    | enum    | config
uration file |         |         | {local,remote_write,on,off} | on       | off       | /var/lib/pgsql/9.3/data/postgresql.conf |        166
(1 row)


> 
> What is iowait?  For pci-e SSD, these drives don't seem very fast...

iostat, top and pg_top never show iowait greater than  0.7%

Tigran.

> 
> merlin
> 


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