From: | Jeff Janes <jeff(dot)janes(at)gmail(dot)com> |
---|---|
To: | Charles Nadeau <charles(dot)nadeau(at)gmail(dot)com> |
Cc: | "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Very poor read performance, query independent |
Date: | 2017-07-12 22:27:27 |
Message-ID: | CAMkU=1xU+GVfK5OmdPcvK9TjzPfn7E3BD5ugYn8iapg8OFy7Lw@mail.gmail.com |
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Lists: | pgsql-performance |
On Wed, Jul 12, 2017 at 3:04 AM, Charles Nadeau <charles(dot)nadeau(at)gmail(dot)com>
wrote:
> Jeff,
>
> Here are the 2 EXPLAINs for one of my simplest query:
>
It looks like dstexterne and flowcompact are both views over flow. Can you
share the definition of those views?
I think the iowait > 12.5% is due to the parallel query execution. But
then the question is, why is it only 25% when you have 10 fold parallelism?
It certainly looks like you are doing more than 4MB/s there, so maybe
something is wrong with the instrumentation, or how you are interpreting
it.
Although it is still less than perhaps it could do. To put a baseline on
what you can expect out of parallel seq scans, can you do something like:
explain (analyze, buffers) select avg(doctets) from flow;
Cheers,
Jeff
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