Re: Solaris Asynchronous I/O & Oracle

In a previous article, Intesar.Ali_at_dcs.warwick.ac.uk (Intesar Ali) says:

>I am wondering if anyone can shed any light on the matter of Asynchronous
>I/O (or AIO) on Solaris 2.3 with Oracle 7.0.16.4.
>
>I have my datafiles partitioned on five different disks, which is not to
>be confused with raw devics (as this is not an option for me,
>unfortunately), and wonder if I can set the parameter async_write=true to
>perform asynchronous writes!!!.

   async_write doesn't buy you anything unless you are using raw devices.   

>Something else I tried was the fact that I set db_writers (in the
>init.ora file) to 10.

   Do you have ten drives on ten controllers? Setting db_writers > 1 will buy you some improvement during heavy write activity, but I would imagine that too many could make things worse. I suggest you experiment. On an idle system, see how long it takes to load a large table with various numbers of db writers. (Note: when you set db_writers to say 2, you will actually get 3: DBWR, DB01, DB02. I guess DBWR stays in charge and delegates writes to the others).

> One of the parameters is DB_BLOCK_WRITE_BATCH, but when I list parameters
>in SQLDBA it does not appear.

   I think that one disappeared a while ago.

>In total I am looking for better I/O throughput.

   Have you determined that you are in fact I/O bottlenecked? are you getting a lot of write_busy_waits? You can tune I/O until you are blue in the face and you will not see any overall improvement unless that is in fact the problem.

>As far as I understand
>setting the async_write=true is a better option than having multiple
>database writers.

   Probably, since it also means moving to raw devices which improves I/O.

• Doug

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