Re: Databse File layout on only 4 drives Ideas?

From: Howard J. Rogers <howardjr2000_at_yahoo.com.au>
Date: Sat, 1 Feb 2003 12:35:53 +1100
Message-ID: <pnF_9.37812$jM5.95874@newsfeeds.bigpond.com>

"Ralf Fernan" <ralphfernan_at_yahoo.com> wrote in message news:UaC_9.14531$rq4.1057151_at_bgtnsc05-news.ops.worldnet.att.net...
> I've see different published sources say different things. The O'Reilly
> book Oracle Perf. Tuning suggests separating indexes and tables into
> separate tablespaces because they are inserted into and read from
> concurrently.

Oh well, if O'Reilly says it, it must be true, and let's not get too concerned about whether they are correct or not!

>The Oracle documentation website says that there is no need
> to do so because indexes are read first.

They are most definitely NOT read from concurrently, and it is highly likely that they won't be written to concurrently, either -because what DBWR decides to flush depends on the state of the LRU list. And index blocks will tend to not be in the same place on the LRU list as the associated table blocks (they contain more 'rows' than a table, and thus tend to be hit more often by readers, and thus tend to be 'hotter' than the table blocks, and thus tend to stay more towards the MRU-end of the LRU list).

HJR Received on Fri Jan 31 2003 - 19:35:53 CST