Re: INSERT - UPDATE throughput oscillating and SSD activity after stopping the client

On 12/02/2016 09:40 AM, Tom DalPozzo wrote:
> Hi,
> I've two tables, t1 and t2, both with one bigint id indexed field and
> one 256 char data field; t1 has always got 10000 row, while t2 is
> increasing as explained in the following.
>
> My pqlib client countinously updates one row in t1 (every time
> targeting a different row) and inserts a new row in t2. All this in
> blocks of 1000 update-insert per commit, in order to get better performance.
> Wal_method is fsync, fsync is on, attached my conf file.
> I've a 3.8ghz laptop with evo SSD.
>
> Performance is measured every two executed blocks and related to these
> blocks.
>
> Over the first few minutes performance is around 10Krow/s then it slowly
> drops, over next few minutes to 4Krow/s, then it slowly returns high and
> so on, like a wave.
> I don't understand this behaviour. Is it normal? What does it depend on?

Have you looked at the Postgres log entries that cover these episodes?

Is there anything of interest there?

>
> Also, when I stop the client I see the SSD light still heavily working.
> It would last quite a while unless I stop the postgresql server, in this
> case it suddenly stops. If I restart the server it remains off.
> I'm wondering if it's normal. I'd like to be sure that my data are safe
> once commited.
>
> Regards
> Pupillo
>
> P.S.: I put this question in general questions as my concern is not if
> the performance is high or not.
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--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com