Re: How to reduce IOWAIT and CPU idle time?

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От Samir Magar
Тема Re: How to reduce IOWAIT and CPU idle time?
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Msg-id CAA=to3hs=qnBTFBYBtQmKXproS6hh_w=uFRcKBvxCx5uCZ-NUQ@mail.gmail.com
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Ответ на Re: How to reduce IOWAIT and CPU idle time?  (Venkata B Nagothi <nag1010@gmail.com>)
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Hello Venkata,

Thank you for the reply!

I forgot to specify the application name.It is ZABBIX tool using postgreSQL database. All types of queries are running slow and i can see application is writing continuously.
Yesterday , i updated effective_io_concurrency to 25 which earlier set as default. But this has not helped me to solve the problem.

Yes, you are right, the database size has grown from 5 GB database to 100 GB database and may be there is problem in slownesss in disk. However we cannot replace the disk right now.

I ran vacuum and analyze manually on all the tables as well. Still it is not helping. Can you think of any other setting which i should enable?


Thanks,
Samir Magar

On Sun, Sep 11, 2016 at 6:04 AM, Venkata B Nagothi <nag1010@gmail.com> wrote:

On Sat, Sep 10, 2016 at 8:49 PM, Samir Magar <samirmagar8@gmail.com> wrote:
Hello,


My Application has normally 25 to 30 connections and it is doing lot of insert/update/delete operation.
The database size is 100GB. 
iowait  is at 40% to 45 % and CPU idle time is at 45% to 50%
TOTAL RAM = 8 GB   TOTAL CPU = 4 

postgresql.conf parametre:

shared_buffers = 2GB
work_mem = 100MB
effective_cache_size = 2GB
maintenance_work_mem = 500MB
autovacuum = off
wal_buffers = 64MB


How can i reduce iowait and CPU idle time. It is slowing all the queries. The queries that used to take 1 sec,it is taking 12-15 seconds.

That does not point out the specific problem you are facing. Queries can slow down for a lot of reasons like as follows -

- Lack of maintenance
- Bloats in Tables and Indexes
- Data size growth
- If writes are slowing down, then it could be because of slow disks

Are you saying that queries are slowing down when there are heavy writes ? Are you referring to SELECTs or all types of queries ?

Regards,
Venkata B N

Fujitsu Australia 

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