Re: Could synchronous streaming replication really degrade the performance of the primary?

On Thu, May 10, 2012 at 8:34 PM, MauMau <maumau307(at)gmail(dot)com> wrote:
> 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.

So they compared the throughput of one server running on a single machine
(non replication case) with that of two servers (i.e., master and
standby) running
on the same single machine (sync rep case)? The amount of CPU/Mem/IO
resource available per server is not the same between those two cases. So
ISTM it's very unfair for sync rep case. In this situation, I'm not
surprised if I
see 50% performance degradation in sync rep case.

> 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...

Though I cannot show the detail for some reasons, as far as I measured
the performance overhead of sync rep by using pgbench, the overhead of
throughput was less than 10%. When measuring sync rep, I used two
set of physical machine and storage for the master and standby, and
used 1Gbps network between them.

Regards,

--
Fujii Masao