Re: Databse File layout on only 4 drives Ideas?

From: Joel Garry <joel-garry_at_home.com>
Date: 3 Feb 2003 16:03:33 -0800
Message-ID: <91884734.0302031603.59a9bb98@posting.google.com>

"Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message news:<LiF_9.37810$jM5.96195_at_newsfeeds.bigpond.com>...

> "Joel Garry" <joel-garry_at_home.com> wrote in message


> > > > I've always had a problem with this statement.  Wouldn't a db buffer

> > > > cache hot-spot like this be a "dirty write" attractor, often flushing

> > > > and making a hot-spot on the disk?

> > >
> > > No, because there's no relationship between the adjacent-ness of blocks

>  on

> > > disk and what DBWR decides to flush.
> >
> > Even in the case of, say, doing an update on everything in a partition
> > that takes an hour during an otherwise low-usage time?

> 
> Probably even in such a case, no. The fact that you're doing a big update
> means a lot of stuff will be flushed, fine. Will that be to adjacent blocks
> on disk? Not necessarily. The blocks within an extent are not physically
> adjacent to each other, raw partitions aside.

Well, I decided not to take this at face value. I copied a quiet db file, ran it into od -c|more, and searched for some data that I knew would be there (ie, a knew a character key was 300007, so I entered /3 0 0 0 0 7), and sure enough, I could see the next row, and the next, and the next, just like import loads them in.

So "not necessarily" is NOT the same as what one can expect is going to be out there on a well-managed disk.

--
@home is bogus.
Everything is a file.

Received on Mon Feb 03 2003 - 18:03:33 CST