Message-ID: <37AC2C75CBA4411F84F5F995EDF91503@maumau>
From: "MauMau" <maumau307@gmail.com>
To: "Claudio Freire" <klaussfreire@gmail.com>
Cc: "Merlin Moncure" <mmoncure@gmail.com>, <pgsql-performance@postgresql.org>
References: 
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In-Reply-To: 
 <CAGTBQpYtod6ee6km0=C+U5yL9Wy5_9Bo7Nm719ymA42-SggLSA@mail.gmail.com>
Subject: Re: Could synchronous streaming replication really degrade the
	performance of the primary?
Date: Thu, 10 May 2012 20:34:43 +0900
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From: "Claudio Freire" <klaussfreire@gmail.com>
On Wed, May 9, 2012 at 7:34 PM, MauMau <maumau307@gmail.com> wrote:
>> Yes, I understand it is natural for the response time of each transaction 
>> to
>> double or more. But I think the throughput drop would be amortized among
>> multiple simultaneous transactions. So, 50% throughput decrease seems
>> unreasonable.

> I'm pretty sure it depends a lot on the workload. Knowing the
> methodology used that arrived to those figures is critical. Was the
> thoughput decrease measured against no replication, or asynchronous
> replication? How many clients were used? What was the workload like?
> Was it CPU bound? I/O bound? Read-mostly?

> We have asynchronous replication in production and thoughput has not
> changed relative to no replication. I cannot see how making it
> synchronous would change thoughput, as it only induces waiting time on
> the clients, but no extra work. I can only assume the test didn't use
> enough clients to saturate the hardware under high-latency situations,
> or clients were somehow experiencing application-specific contention.

Thank you for your experience and opinion.

The workload is TPC-C-like write-heavy one; DBT-2. They compared the 
throughput of synchronous replication case against that of no replication 
case.

Today, they told me that they ran the test on two virtual machines on a 
single physical machine. They also used pgpool-II in both cases. In 
addition, they may have ran the applications and pgpool-II on the same 
virtual machine as the database server.

It sounded to me that the resource is so scarce that concurrency was low, or 
your assumption may be correct. I'll hear more about their environment from 
them.

BTW it's pity that I cannot find any case study of performance of the 
flagship feature of PostgreSQL 9.0/9.1, streaming replication...

Regards
MauMau