Re: postgresql tuning with perf

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
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