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Re: pg_basebackup blocking all queries with horrible performance

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: Lonni J Friedman <netllama(at)gmail(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Craig Ringer <ringerc(at)ringerc(dot)id(dot)au>, Jerry Sievers <gsievers19(at)comcast(dot)net>, pgsql-admin(at)postgresql(dot)org
Subject: Re: pg_basebackup blocking all queries with horrible performance
Date: 2012-06-20 12:02:57
Message-ID: CA+U5nMJmuYsFD35SvjhKat0Fcd=8DiALxB8JUdY9kFvF3=bStw@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-adminpgsql-hackers
On 13 June 2012 02:39, Magnus Hagander <magnus(at)hagander(dot)net> wrote:

>> I'm running the following, which gets piped over ssh to a remote
>> server (at gigabit ethernet speed):
>> pg_basebackup -v -D - -x -Ft -U postgres
>>
>> One thing that I've discovered is that if I throttle back the speed of
>> what is getting piped to the remote server, that directly correlates
>> to the load on the server.
>
> That seems to indicate that you're overloading the I/O system... Or
> the CPU, but more likely I/O.

CPU utilisation of ssl connections is bad. If network bandwidth is
good, perhaps running WALSender at full speed with encryption can tank
the server.

An effect related to cacheing of WAL files? Perhaps we need to mark
them as FADV_DONTNEED at some point.

Hard to say without detailed analysis.

-- 
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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