On 19/09/14 09:10, Mkrtchyan, Tigran wrote:
----- Original Message -----
From: "Mark Kirkwood" <mark.kirkwood@xxxxxxxxxxxxxxx>
To: "Merlin Moncure" <mmoncure@xxxxxxxxx>, "Tigran Mkrtchyan" <tigran.mkrtchyan@xxxxxxx>
Cc: "postgres performance list" <pgsql-performance@xxxxxxxxxxxxxx>
Sent: Thursday, September 18, 2014 10:56:36 PM
Subject: Re: postgres 9.3 vs. 9.4
On 19/09/14 08:32, Merlin Moncure wrote:
On Thu, Sep 18, 2014 at 4:58 AM, Mkrtchyan, Tigran
<tigran.mkrtchyan@xxxxxxx> 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?
Yes, does look suspicious. It *could* be that the 9.4 case is getting
unlucky and checkpointing just before the end of the 60s run, and 9.3
isn't.
10 minutes run had the same results.
Is there some kind of statistics which can tell there time is spend?
Or the only way is to run on solaris with dtrace? For me it's more important
to find why I get only 1500tps with 9.3. The test with 9.4 was just a hope for
a magic code change that will give me a better performance.
Interesting. With respect to dtrace, you can use systemtap on Linux to
achieve similar things.
However before getting too carried away with that - we already *know*
that 9.4 is spending longer in END (i.e commit) than 9.3 is. I'd
recommend you see what wal_sync_method is set to on both systems. If it
is the same, then my suspicion is that one of the SSD's needs to be
trimmed [1]. You can do this by running:
$ fstrim /mountpoint
Also - are you using the same filesystem and mount options on each SSD?
Cheers
Mark
[1] if fact, for the paranoid - I usually secure erase any SSD before
performance testing, and then check the SMART counters too...
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