Re: Explain what is Oracle Logical IO

"Niall Litchfield" <niall.litchfield_at_dial.pipex.com>

> > Logical I/O != Physical I/O
>
> But Physical I/O = Logical I/O ta da.
>
> Ok what I mean is logical I/O consists of *every* io request (usually for a
> database block read or update, but also logs etc) that Oracle makes.
> Physical I/O are those io requests that result in a physical disk access.

True. We need to revise that formula of "Logical I/O != Physical I/O" to indicate that a logical i/o could result in a physical i/o even though it is not a physical i/o in itself.

Which of course raises that pesky question.. just where the heck do all those deleted bytes go after a physical i/o has completed? After all, the number #1 rule in the universe is that nothing can be destroyed (the state merely change). Deleted bytes do not change into energy (I have yet to burn a disk due to too many deleted bytes). I've crawled around the bottom of the EMC array (with a magnifying glass) and have yet to see any of those deleted bytes. So what happens to them?

--
Billy