Async/Sync IO

[Halo]

How can I tell if the OS supports/is Async or Sync IO?? OS is Sun Solaris 2.6. Thanx.

[marist89]

According to "Oracle 8i & Unix Performance Tuning" by Ahmed Alomari, Solaris 2.6 AIO is supported both on file systems and raw devices. However, he recommends disabling AIO when running on 2.6 with file systems. (The init.ora parameter is disk_asynch_io=false)

You can check this book out at [url]http://www.amazon.com/exec/obidos/ASIN/0130187062/o/qid=975958998/sr=8-1/ref=aps_sr_b_1_3/106-3395441-2765254[/url]

[Halo]

The parameter disk_async_io is set to True by default and I had set dbwr_io_slaves is set to 1. I just read that if disk_async_io is set to true, then dbwr_io_slaves should not be used. Is this correct?? The problem is that I notice a bottleneck with the DBWR and even with the LGWR. Is there a way to tune this?? I have only 1 CPU on the server. thanx.

[marist89]

Yes, if you are running AIO, you would not need to use dbwr_io_slaves. However, you may want to configure more than one DBWR process to help with your writes.

You may want to look to see if any of your devices are getting saturated. (iostat -xdM 5)

[Halo]

But I don't think I can use more than 1 DBWR with only 1 CPU!!

[marist89]

Sure you can. I just set up 4 dbwrs on a single CPU box. If your CPU is not swamped and you have adequate I/O bandwidth, go ahead, knock yourself out.

[Halo]

Cool. What exactly do you mean by 'adequate I/O bandwidth'. Can you explain?? thanx.

[marist89]

4 dbwr processes on 1 5400RPM disk = performance sucks
4 dbwr processes on stiped 15KRPM FCAL disks = good performance.

If you have 4 dbwr processes configured and they are all pumping data to the same disk, there will be disk contention. If you have 4 dbwr processes configured and the CPU is spinning at around 80-90% and the disks are < 50% busy, you are doing pretty good.

[Halo]

Thanx. I will try it out.