Oracle Database Discussions

Hello guys,
at my current project i am performing some performance tests for oracle data guard. The question is "How does a LGWR SYNC transfer influences the system performance?"
To get some performance values, that i can compare i just built up a normal oracle database in the first step.

Now i am performing different tests like creating "large" indexes, massive parallel inserts/commits, etc. to get the bench mark.

My database is an oracle 10.2.0.4 with multiplexed redo log files on AIX.

I am creating an index on a "normal" table .. i execute "dbms_workload_repository.create_snapshot()" before and after the CREATE INDEX to get an equivalent timeframe for the AWR report.
After the index is built up (round about 9 GB) i perform an awrrpt.sql to get the AWR report.

And now take a look at these values from the AWR

                                                                   Avg
                                             %Time  Total Wait    wait     Waits
Event                                 Waits  -outs    Time (s)    (ms)      /txn
---------------------------- -------------- ------ ----------- ------- ---------
......
......
log file parallel write              10,019     .0         132      13      33.5
log file sync                           293     .7           4      15       1.0
......
......

How can this be possible?

Regarding to the documentation

-> log file sync: http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/waitevents003.htm#sthref3120

Wait Time: The wait time includes the writing of the log buffer and the post.

-> log file parallel write: http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/waitevents003.htm#sthref3104

Wait Time: Time it takes for the I/Os to complete. Even though redo records are written in parallel, the parallel write is not complete until the last I/O is on disk.

This was also my understanding .. the "log file sync" wait time should be higher than the "log file parallel write" wait time, because of it includes the I/O and the response time to the user session.
I could accept it, if the values are close to each other (maybe round about 1 second in total) .. but the different between 132 seconds and 4 seconds is too noticeable.

Is the behavior of the log file sync/write different when performing a DDL like CREATE INDEX (maybe async .. like you can influence it with the initialization parameter COMMIT_WRITE??)?
Do you have any idea how these values come about?


Any thoughts/ideas are welcome.

Thanks and Regards