Re: How to reduce IOWAIT and CPU idle time?

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От Jeff Janes
Тема Re: How to reduce IOWAIT and CPU idle time?
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Msg-id CAMkU=1ywsxuMMok3Ux9EUmvqWQB4zdvjtHo-=w9qdxDwSy45zg@mail.gmail.com
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Ответ на How to reduce IOWAIT and CPU idle time?  (Samir Magar <samirmagar8@gmail.com>)
Ответы Re: How to reduce IOWAIT and CPU idle time?
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On Sat, Sep 10, 2016 at 3:49 AM, 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.

What changed between the 1 sec regime and the 12-15 second regime?  Just growth in the database size?

Index-update-intensive databases will often undergo a collapse in performance once the portion of the indexes which are being rapidly dirtied exceeds shared_buffers + (some kernel specific factor related to dirty_background_bytes and kin)

If you think this is the problem, you could try violating the conventional wisdom by setting shared_buffers 80% to 90% of available RAM, rather than 20% to 25%.

Cheers,

Jeff

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