Re: Exclusive Unix file system file write locks and Oracle and Veritas

Under Unix file system, writers lock readers and readers lock writers independently of anything that Oracle is doing. The lock is on the inode to ensure that a read cannot read data that is changing.

This also happens under Veritas, but the nature of vxfs makes the lock (usually) a little shorter. Also the latest version of veritas has further optimisation in it for 'quick db' which I think helps further.

The main benefit for 'small files' is in mixing parallel query and TEMP. If you run create index in parallel, then all the query slaves are likely to be reading and writing to TEMP at the same time and interfering at the O/S level, so it is better to have N files in temp matching the degree of parallelism to reduce the probability of O/S collisions.

(This is the extreme case of course, but the same idea holds any tablespace which is likely to be subject to large numbers of concurrent reads and writes - Rollback segment tablespaces are __likely__ to be the next candidate on busy systems).

--

Jonathan Lewis
Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk

NetComrade wrote in message <37d93dab.269121198_at_news.earthlink.net>...
>What I really meant, what are the UNIX constraints on Oracle (or
>should I say veritas constraints), since theoretically on a UFS there
>are locks placed on a file upon writes. DOes Veritas do the same
>thing? As for Oracle locking, I really don't have any on any of my
>machines, expect for some MR locks, which are constantly there, and I
>don't really know what they mean, but they are placed by PMON, so it
>must be cleaning up something.
>
Received on Fri Sep 10 1999 - 13:11:51 CDT