Re: LGWR process priorities on the Solaris platform

  • From: "Tanel Poder" <tanel.poder.003@xxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 12 Jul 2006 18:54:53 +0300


> amounts of "log file sync" was observed. We started checking with 
> developers that apps hadn't increased commit rates, but

You don't check such things with developers, you measure 'em yourself (from 
statspack or AWR for example).

>       After doing a little reading up I came across Steve Adams' note on 
> process priorities with regards the background processes. Opinion 
> seems to be divided on whether it's wise to place the BG procs into 
> real-time and leave user process in shared? The only concern I have is 
> that profiling would need to be introduced into the DB to try to stop 
> the job/schedule J00x BG processes getting carried away.

As Alex said, your problem is probably somewhere else, than in the priorities.
Increasing LGWR priority would be justified if:

1) High user waits for "log file sync"


2) LGWR itself is NOT waiting significant time for "log file parallel write"


3) OS statistic "OS Wait-cpu (latency) time" for LGWR's session is a 
significant amount of logwriter's time (you've got to sample this over an 
interval, subtract CPU and wait times from the interval and hopefully then you 
can compare the remainder to the statistics value. And you need 
timed_os_statistics=true or statistics_level=all for that)

..if those conditions aren't satisfied, then you won't gain from increasing 
LGWRs priority even if your CPUs are 100% utilized.

>       The other question I have for Solaris admins on the list, would 
> process priorities be remembered by process signature across process 
> restarts? Ie if you shutdown the DB the LGWR process will get a new 
> process ID on each restart, so would the Solaris O/S remember and keep 
> hampering the LGWR process based on what it remembered about it 
> before?

As far as I know it's based on process or thread ID's, it wouldn't make sense 
to have it based on image as some systems have tens of thousands of processes 
running from the same image.

As you're on 10g, I'd suggest you to check the AWR stats and compare its 
reports between problematic and non-problematic periods.


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