Subject: Re: postgresql tuning with perf
To: Purav Chovatia <puravc@gmail.com>, pgsql-performance@postgresql.org
References: 
 <CADrzpjHuvgoTNOQosjHDaJ8YW=jDiwCn8u2h8A1HWRTaPzVc5w@mail.gmail.com>
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <83f4911f-432f-8725-8fff-887753654396@2ndquadrant.com>
Date: Mon, 23 Oct 2017 22:55:56 +0200
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On 10/23/2017 09:19 PM, Purav Chovatia wrote:
> Hello Experts,
> 
> We are trying to tune our postgresql DB using perf.

Can you share some of the perf reports, then?

> We are running a C program that connects to postgres DB and calls
> very simple StoredProcs, one each for SELECT, INSERT & UPDATE.
> 
> The SPs are very simple. 
> *SELECT_SP*:
> CREATE OR REPLACE PROCEDURE query_dept_new(p1 IN numeric, p2 OUT
> numeric,p3 OUT numeric,.......,p205 OUT numeric) AS
> BEGIN
>     SELECT c2,c3,......,c205
>         INTO p2,p3,.......,p205
>         FROM dept_new
>         WHERE c1 = p1;
> END;
> 
> *UPDATE_SP*:
> CREATE OR REPLACE PROCEDURE query_dept_update(p1 IN numeric, p2 IN
> numeric,........,p205 IN numeric) AS
> BEGIN
>     update dept_new set  c2 = p2,c3 = p3,.....,c205 = p205 
>         WHERE c1 = p1;
> commit;
> END;
> 
> *INSERT_SP*:
> CREATE OR REPLACE PROCEDURE query_dept_insert(p1 IN numeric, p2 IN
> numeric,.....,p205 IN numeric) AS
> BEGIN
> insert into dept_new values(p1,p2,.....,p205);
> commit;
> END;
> 
> As shown above, its all on a single table. Before every test, the table
> is truncated and loaded with 1m rows. WAL is on a separate disk.
> 

It'd be nice if you could share more details about the structure of the
table, hardware and observed metrics (throughput, ...). Otherwise we
can't try reproducing it, for example.

> Its about 3x slower as compared to Oracle and major events are WAL
> related. With fsync=off or sync_commit=off it gets 10% better but still
> far from Oracle. Vacuuming the table does not help. Checkpoint too is
> not an issue. 

So how do you know the major events are WAL related? Can you share how
you measure that and the measurements?

> 
> Since we dont see any other way to find out what is slowing it down, we
> gathered data using the perf tool. Can somebody pls help on how do we go
> about reading the perf report.

Well, that's hard to do when you haven't shared the report.

regards

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


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