From: | Antonio Carlos Salzvedel Furtado Junior <acsfj08(at)inf(dot)ufpr(dot)br> |
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To: | pgsql-novice(at)postgresql(dot)org |
Subject: | Performance issue with virtualized DB |
Date: | 2012-08-07 22:05:51 |
Message-ID: | CAERqmVrbwek4eXSndwFGajJxuTrRQr+UDQ5BsmdxMzssEtdkVg@mail.gmail.com |
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Lists: | pgsql-novice |
Hello PostgreSQL users,
I'm running PostgreSQL 9 in a VM, sing KVM as hypervisor. The whole
database is loaded in a RAM file system.
As other hypervisors, there are some parameters to limit CPU that are
very important to me. I usually need to change the values of these
parameters.
However I'm having a bit of unexpected performance problems. Shouldn't
the query execution times vary linearly with the allocated CPU?
I ran some tests, and I found out that the costs vary "kind of"
linearly until some point. However if I give my VM less than about 20%
of the available CPU, the costs "explode".
The problem is that I need to run multiple VMs on the same host, and I
can't afford that much deterioration. I never heard about a "safe
limit" for CPU allocation. I always thought that CPU would affect the
query linearly.
Regards,
Antonio Carlos Furtado
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