Re: Vertias ODM and Oracle 9i

From: Yong Huang <yong321_at_yahoo.com>
Date: 3 Dec 2004 07:52:22 -0800
Message-ID: <b3cb12d6.0412030752.1f84df32@posting.google.com>

rlro99_at_hotmail.com (Ralph) wrote in message news:<e2c49cae.0412020318.25c0c2d5_at_posting.google.com>...
> rlro99_at_hotmail.com (Ralph) wrote in message news:<e2c49cae.0411300747.50aa4f3f_at_posting.google.com>...
> > Oracle 9.2.0.4 (64-bit)
> > Veritas version 1
> > Solaris 9
> >
> > We have performed various tests on Oracle db_file_scattered_read
> > performance in various combinations of:
> >
> > VxFS - with and without ODM
> > VxVM partition - with and without ODM
> > VTOC partition - with and without ODM
> >
> > and tried various combinations of db_block_size.
> >
> > Whilst we can get VxFS and any raw partition to perform IOs in
> > db_file_multiblock_read_count * db_block_size requests, any use of ODM
> > always results in the transfers being of db_block_size. This is
> > clearly less effcient since more requests must be issued for this kind
> > of read.
> >
> > This seems at odds with the documentation which claims that odm_io()
> > will perform sequential reads/writes, direct read/writes, scattered
> > reads, dbwr batch writes etc in the most efficient manner available.
> >
> > Is there any way that the behaviour of ODM can be influenced such that
> > scattered reads are performed in db_file_multiblock_read_count *
> > db_block_size requests?
> >
> >
> > Cheers
> >
> > Ralph

>...

>
> A summary of the results are available here
>
> http://www.jorgensen.org.uk/odm.pdf
>
> These were obtained by sar odmstat statspack etc.
>
> We are only interested in the scattered read perfromance, rather than
> the overall IO performance.

Excellent test, Ralph. I suggest you open a Tar with Oracle and a ticket with Veritas. Their partnership may assign one person from Veritas and one from Oracle to handle your Tar.

Now I know that your observation of db_block_size used by ODM is obtained by sar column blks/s divided by r+w/s. (I thought you were saying using ODM, you don't see db_file_scattered_read events.) For my curiosity, when you run full table scans in Oracle, does the Oracle shadow process perform pread (or pread64) or readv? Is it different on ODM and non-ODM? My guess is no difference; ODM hides the details below the system call level.

Yong Huang Received on Fri Dec 03 2004 - 09:52:22 CST