Re: Excessive Logical and Physical I/O

> > Building a read consistent image is on a block by block basis. If one
> > user only needs 1MB of read consistent images, then they only rebuild
> > the number of blocks to satisfy that request.
> >
> > HTH,
> > Brian
>
> Does that mean that rollbacks that are allowed to overextend don't
> have a negative impact on performance...? because everything I have
> read points to the opposite...

I'm having a hard time understanding how you went from my comments to your comments. I must have missed the logic somewhere along the lines there.

And what do you mean by "overextend"? A rollback segment can extend, up to MAXEXTENTS. It can't extend past that. MAXEXTENTS is the maximum number of extents. How can you go over this amount?

Any time an extent has to be allocated or deallocated, work has to be done. If your task requires an allocation or deallocation of an extent, then the time it takes to complete the task will be longer than if you were able to accomplish the same task without the allocation/deallocation of that extent. Will that have a negative impact on performance? It depends on many factors. I don't subscribe to the theory that just because something takes a little longer, it negatively impacts performance. To me, negative (or positive) performance impacts are measured by user pain (or joy) over the job that they are trying to accomplish. If the user doesn't notice anything, and therefore they are not experiencing any pain, then the allocation of extents is not causing a performance problem. If you stop the allocation of extents, and the user is happy with the results, because it is a noticable improvement, then there was a negative performance impact.

HTH,
Brian

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Brian Peasland
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