This blog contains experience gained over the years of implementing (and de-implementing) large scale IT applications/software.

HowTo: Read ST03 IO Redo Log Per Hour, Log Switches in SAP

Within the SAP St03 transaction, the analysis view “Wait Event Analysis -> IO Redo Log Per Hour” or “Redo Log Switches” (from SAPKB70029 onwards), is able to show you the Oracle redo log switch measure.
SAP Oracle IO Redo Log Per Hour
You will need to adjust the “Minimum Time Between Switches[sec]” and “Maximum Time Between Switches [sec]” values, then click the refresh button.
The results tell you in what hour period, the number of times a redo log switch was performed where the time between the switches was within your defined range.
As an example, the screen shot above shows that on 29-11-2013 between 04:00 and 05:00, a redo log switch occurred on only 1 occasion where the time between one log switch and another was within 120 seconds (2 minutes).
It’s difficult to say if too many log switches is an actual problem for your specific database, but I would tend to investigate any database where the logs are switching on more than a couple of occasions a day, within 60 seconds.

Solaris 10 – Asynch I/O on UFS – Not Really

Whilst investigating a performance issue on an Oracle database running on Solaris 10, I had to do a little digging to discover exactly how asynchronous I/O is implemented within Oracle when the database is using the UFS filesystem.

It was not as straightforward as i thought, because I had to start from the beginning and not trust any current Oracle settings.  For example, FILESYSTEMIO_OPTIONS was set to “ASYNCH” in the spfile.
This would normally indicate that a DBA has specifically determined that ASYNCH I/O is possible and that they do not want to use DIRECTIO (or concurrent I/O).

Yet, reading the SAP notes, you would think that this is a moot point.
SAP note  830576 “Parameter recommendations for Oracle 10g” v227 clearly states that Oracle 10.2 on Solaris with UFS filesystems, supports asynchronous I/O, so therefore set the FILESYSTEMIO_OPTIONS to “SETALL”.

However, if you have access to “My Oracle Support” you can check Oracle document “SOLARIS: Asynchronous I/O (AIO) on Solaris (SPARC) servers (Doc ID 48769.1)” which explains that, in Solaris with UFS, Oracle does not actually perform asynchronous I/O at the kernel (Solaris) level.  Instead, Solaris simulates AIO by performing parallel writes (calls pwrite() ) but to Oracle it still looks and feels like KAIO.
So, the details in the SAP note are not exactly accurate.  AIO is not supported in Solaris, but is simulated.  Also, the simulation is just issuing more parallel I/O requests. 

If your disk sub-system is slow, it’s still going to be slow, but Oracle writes might be slightly faster if you handle/tune for more parallel requests at the storage layer.

Here’s a nice article that explains it really well: