Hi, Andy,
Impact of other VMs is reflected as %steal time. And it's only this
specific UPDATE query on this specific table that ever exhibits the problem,
as measured over many days, a query that must represent something like <2%
of all queries run against the DB over the same period and <5% of all other
UPDATE queries running on the system across other tables in the same
tablespace over, again, the same period.
V.
----- Original Message -----
From: "Andy Colson" <andy@xxxxxxxxxxxxxxx>
To: "Vlad Romascanu" <vromascanu@xxxxxxxxxxxxx>;
<pgsql-performance@xxxxxxxxxxxxxx>
Sent: Thursday, September 17, 2009 9:45 AM
Subject: Re: Possible causes of sometimes slow single-row UPDATE
with trivial indexed condition?
Vlad Romascanu wrote:
Problem occurs when running (in production) Postgres 8.3.7 64-bit (from
RPM) on Ubuntu 8.04.2, on an Amazon EC2 (xen) "Large" instance (8GB RAM),
with the DB on a 50GB EC2 block device.
Problem does not occur when running (in staging/pre-production) Postgres
8.3.5 32-bit (from RPM) on Ubuntu 8.04.1, on a less beefy Amazon EC2
(xen) "Small" instance, with the DB on a 5GB EC2 block device.
I am running with slow query logging on, and somewhat inexplicably I've
been getting the following slow UPDATE query several times in the past
weeks (I'm also including some context lines above and below):
I'm not sure how Amazon vm's work, but are there multiple vm's on one box?
Just because your vm has zero cpu/disk does not mean the host isn't pegged
out of its mind.
Does Amazon give any sort of host stats?
-Andy
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