Re: directio performance question

Hi, I think your test is not a good test for this purpose. You are doing a DDL. I am not sure what gets written to redo in this case. I think it is probably just the DDL SQL without the physical data ( or logical changes only ).

Although writes do affect db writers, however because they are not real time, using timing in sqlplus won't tell you anything, unless you happen to bump into a checkpoint.

So the best way to test this is to test your log writer, not db writer.

If you test DML you would notice big difference. I have benchmarked inserts before. Your main interest would be log writer CPU usage and 'log file sync' wait time. DIO performs fairly close to QIO.

Solaris has forcedirectio Veritas has convosync option that you can set to "direct".

Perform a simple test without DIO of inserting a large number of rows and get the difference of 'log file sync' before and after and then do the same with DIO. The difference is several fold.

It is harder to collect exact redo CPU % usage without proper tools, but you can get a rough idea using ps.

Of course your redo needs to be on the DIO volume. Received on Mon Jul 07 2003 - 20:30:36 CDT