Skip site navigation (1) Skip section navigation (2)

Re: slow i/o

From: "Jignesh K(dot) Shah" <J(dot)K(dot)Shah(at)Sun(dot)COM>
To: Junaili Lie <junaili(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: slow i/o
Date: 2006-08-30 18:17:02
Message-ID: 44F5D61E.6090103@sun.com (view raw or flat)
Thread:
Lists: pgsql-performance
The bgwriter parameters changed in 8.1

Try

bgwriter_lru_maxpages=0
bgwriter_lru_percent=0

to turn off bgwriter and see if there is any change.

-Jignesh


Junaili Lie wrote:
> Hi Jignesh,
> Thank you for my reply.
> I have the setting just like what you described:
> 
> wal_sync_method = fsync
> wal_buffers = 128
> checkpoint_segments = 128
> bgwriter_all_percent = 0
> bgwriter_maxpages = 0
> 
> 
> I ran the dtrace script and found the following:
> During the i/o busy time, there are postgres processes that has very 
> high BYTES count. During that non i/o busy time, this same process 
> doesn't do a lot of i/o activity. I checked the pg_stat_activity but 
> couldn't found this process. Doing ps revealed that this process is 
> started at the same time since the postgres started, which leads me to 
> believe that it maybe background writer or some other internal process. 
> This process are not autovacuum because it doesn't disappear when I  
> tried turning autovacuum off.
> Except for the ones mentioned above, I didn't modify the other 
> background setting:
> MONSOON=# show bgwriter_delay ;
>  bgwriter_delay
> ----------------
>  200
> (1 row)
> 
> MONSOON=# show bgwriter_lru_maxpages ;  bgwriter_lru_maxpages
> -----------------------
>  5
> (1 row)
> 
> MONSOON=# show bgwriter_lru_percent ;
>  bgwriter_lru_percent
> ----------------------
>  1
> (1 row)
> 
> This i/o spike only happens at minute 1 and minute 6 (ie. 10.51, 10.56) 
> . If I do select * from pg_stat_activity during this time, I will see a 
> lot of write queries waiting to be processed. After a few seconds, 
> everything seems to be gone. All writes that are not happening at the 
> time of this i/o jump are being processed very fast, thus do not show on 
> pg_stat_activity.
> 
> Thanks in advance for the reply,
> Best,
> 
> J
> 
> On 8/29/06, *Jignesh K. Shah* <J(dot)K(dot)Shah(at)sun(dot)com 
> <mailto:J(dot)K(dot)Shah(at)sun(dot)com>> wrote:
> 
>     Also to answer your real question:
> 
>     DTrace On Solaris 10:
> 
>     # dtrace -s /usr/demo/dtrace/whoio.d
> 
>     It will tell you the pids doing the io activity and  on which devices.
>     There are more scripts in that directory like iosnoop.d, iotime.d
>     and others which also will give
>     other details like file accessed, time it took for the io etc.
> 
>     Hope this helps.
> 
>     Regards,
>     Jignesh
> 
> 
>     Junaili Lie wrote:
>      > Hi everyone,
>      > We have a postgresql 8.1 installed on Solaris 10. It is running fine.
>      > However, for the past couple days, we have seen the i/o reports
>      > indicating that the i/o is busy most of the time. Before this, we
>     only
>      > saw i/o being busy occasionally (very rare). So far, there has
>     been no
>      > performance complaints by customers, and the slow query reports
>     doesn't
>      > indicate anything out of the ordinary.
>      > There's no code changes on the applications layer and no database
>      > configuration changes.
>      > I am wondering if there's a tool out there on Solaris to tell which
>      > process is doing most of the i/o activity?
>      > Thank you in advance.
>      >
>      > J
>      >
> 
> 

In response to

Responses

pgsql-performance by date

Next:From: Alex HaywardDate: 2006-08-30 18:22:18
Subject: Re: performance problems.
Previous:From: Jim C. NasbyDate: 2006-08-30 16:26:57
Subject: Re: performance problems.

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group