Re: db_writer_processes and Async IO ???
- From: Jared Still <jkstill@xxxxxxxxx>
- To: mccdba1@xxxxxxxxx
- Date: Mon, 17 Aug 2009 10:16:01 -0700
On Mon, Aug 17, 2009 at 9:39 AM, Jared Still <jkstill@xxxxxxxxx> wrote:
> On Sat, Aug 15, 2009 at 3:36 PM, dba1 mcc <mccdba1@xxxxxxxxx> wrote:
>
>> db_writer_processes = 2
>>
>> filesystemio_options = asynch
>> DISK_ASYNCH_IO = true
>> TAPE_ASYNCH_IO = true
>>
>> Based on what I know "db_writer_processes " and "filesystemio_options =
>> asynch" are exclusive. Can anyone tell me database will use whiche one?
>>
>
> This should help answer your question:
>
> ps -flu<oracle_owner> | grep dbw.*$ORACLE_SID
>
>
After re-reading this I realized it wasn't terrible helpful.
Here's a test I performed:
This is 10gR2 on Linux ES 4
alter system set db_writer_processes=2 scope=spfile;
verify the sync parameters:
NAME VALUE
VAL? MOD? MOD?
------------------------- --------------------------------------------------
---- ---- ----
disk_asynch_io TRUE
Y N N
tape_asynch_io TRUE
Y N N
filesystemio_options ASYNCH
N N N
restart the database in nomount mode
start a trace on each of the 2 db writer processes
alter database mount
alter database open
logon and create a table:
create table xxx
as
select * from dba_objects
where 1=0;
insert /*+ append */ into xxx
select * from dba_objects
/
Now shutdown the database.
Examine the trace files and find lots of io_submit calls
Linux man page says that this is an async_io call.
So, it would appear that both multiple db writers and
async IO are being used.
One parameter does not preclude the use of the other.
I am sure someone else can give a better explanation of
the async IO calls, as I only know what I read in the man
page about them
Jared Still
Certifiable Oracle DBA and Part Time Perl Evangelist
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