Re: slow i/o
От | Jignesh K. Shah |
---|---|
Тема | Re: slow i/o |
Дата | |
Msg-id | 44F5D61E.6090103@sun.com обсуждение исходный текст |
Ответ на | Re: slow i/o ("Junaili Lie" <junaili@gmail.com>) |
Ответы |
Re: slow i/o
("Junaili Lie" <junaili@gmail.com>)
|
Список | 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.K.Shah@sun.com > <mailto:J.K.Shah@sun.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 > > > >
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