In some of our benchmarks with our hybrid application on Oracle 8.1.7 , Oversizing
session_cached_cursors would HARM performance greatly . Our Optimal Value is 50
-----Original Message-----
Sent: Wednesday, November 27, 2002 12:20 AM
To: Multiple recipients of list ORACLE-L
Deborah,
First, don't remove Oracle's RedoLog duplexing, you may regret about it
later (see recent thread on this issue).
Second, if what you are telling ("logs are about 100 MB in 2 groups of 20
members each") is accurate, then this is your main problem. If you have
your log switches on avg 2.5 per day, change your RedoLog configuration to
be: 3 (or 4) groups, 3 members each (if you can put them on separate
"physical" devices, if not - 2 members should suffice), and you can make
them smaller, like 50Mb (or even smaller). You will have more log switches
per day, but it's perfectly fine as long, as don't have them every 5 min.
And "old school" is still right about not putting RedoLogs onto RAID5.
Igor Neyman, OCP DBA
[EMAIL PROTECTED]
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Tuesday, November 26, 2002 1:00 PM
> We are on 9.2.0.2, Solaris 8 on Sunfire 3800 with 16 GB memory and 128 MB
> on a hardware-controlled, mirrored RAID5 StorEdge T-3 Array.
>
> Periodically throughout the day the LGWR background process clocks 20+
> minutes of CPU time while actual CPU usage is quite low. I ran a statspack
> report and for a 45-minute period that included the slow LGWR process.
>
> The top 5 timed events in my 45-minute report are:
>
> CPU time 1,295 60.41
> db file sequential read 392,516 341 15.91
> db file scattered read 70,245 168 7.85
> log file sync 26,916 133 6.22
> library cache pin 22 59 2.76
>
> (Now that the top 5 is "timed" events, 3 spots almost always include CPU
> and the db file reads, so I only get two other events, usually log file
> sync, sometimes enqueue or latch free.)
>
> Statspack also shows the log file parallel write had 28,589 timeouts in
> that 45 minute period--rather typical for us.
>
> I have session_cached_cursors set to 150.
>
> I am considering the following:
>
> 1. Removing my own redo log duplexing (mirroring) since redo logs are on
> the mirrored, hardware-controlled RAID5 disk array. (I know, I know)
> My sysadmin talked to the sun engineer yesterday and he said this is
> "old school" thinking that redo logs should not be on RAID5. He said
> because the RAID controller caches to memory all IO requests from
> the CPUs, all physical writes to disk are done behind the scenes
> (known as writebehind). He says the system is NOT waiting for IO.
>
> 2. Increasing redo log size (again). For the most part, log switches
> average 2.5 per day, although there were 20 times in the last month of 3-7
> switches in a half hour. My logs are about 100 MB in 2 groups of 20
members
> each.
>
> 3. Upping the session_cached_cursors to ? (in response to the library
cache
> pin event).
>
> Or is there a better option I'm overlooking?
>
> I would appreciate some advise on the best approach to resolve the slow
> LGWR process, especially your thoughts on option 1.
>
> Thanks,
> Debi
> Deborah Lorraine, DBA
> University of California, Davis
> [EMAIL PROTECTED]
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Deborah Lorraine
> INET: [EMAIL PROTECTED]
>
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Author: Igor Neyman
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