From: Justin Pryzby <pryzby@telsasoft.com>
To: Rambabu g <rambabu.g2564@gmail.com>
Cc: pgsql-performance@lists.postgresql.org
Subject: Re: HIGH IO and Less CPU utilization
Date: Tue, 29 Mar 2022 13:24:53 -0500
Message-ID: <20220329182453.GA28503@telsasoft.com> (raw)
In-Reply-To: <CADdgF6ecxpubq-wm4bcDCyj3yt6uNjJgXKcdCS2Jn+NvE4abFw@mail.gmail.com>
References: <CADdgF6ecxpubq-wm4bcDCyj3yt6uNjJgXKcdCS2Jn+NvE4abFw@mail.gmail.com>
Hi,
Thanks for providing all this info.
On Tue, Mar 29, 2022 at 11:34:18PM +0530, Rambabu g wrote:
> Hi All,
>
> We have an issue with high load and IO Wait's but less cpu on postgres
> Database, The emp Table size is around 500GB, and the connections are very
> less.
What indexes are defined on this table ?
How large are they ?
> Red Hat Enterprise Linux Server release 7.9 (Maipo)
> PostgreSQL 11.15 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44), 64-bit
>
> shared_buffers=12GB
> work_mem=128MB
> 14428 | 04:45:59.712892 | active | INSERT INTO target (empno, name)
> SELECT empno, '' AS name FROM (select distinct empno from emp where sname='test'
> and tp='EMP NAME 1' LIMIT 10) AS query ;
Is the only only problem query, or just one example or ??
Are your issues with loading data, querying data or both ?
> -bash-4.2$ iostat -x
It shows that you only have a few filesystems in use.
It's common to have WAL and temp_tablespaces on a separate FS.
That probably wouldn't help your performance at all, but it would help to tell
what's doing I/O. Is there anything else running on the VM besides postgres ?
You can also check:
SELECT COUNT(1), wait_event FROM pg_stat_activity GROUP BY 2 ORDER BY 1 DESC;
And the pg_buffercache extension:
SELECT COUNT(nullif(isdirty,'f')) dirty, COUNT(1) all, COALESCE(c.relname, b.relfilenode::text) FROM pg_buffercache b LEFT JOIN pg_class c ON b.relfilenode=pg_relation_filenode(c.oid) GROUP BY 3 ORDER BY 1 DESC,2 DESC LIMIT 9;
> Hypervisor vendor: KVM
Are KSM or THP enabled on the hypervisor ?
tail /sys/kernel/mm/ksm/run /sys/kernel/mm/transparent_hugepage/khugepaged/defrag /sys/kernel/mm/transparent_hugepage/enabled /sys/kernel/mm/transparent_hugepage/defrag
--
Justin
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Subject: Re: HIGH IO and Less CPU utilization
In-Reply-To: <20220329182453.GA28503@telsasoft.com>
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