How many RBS waits are too many?

I'm using Guy Harrison's script that shows the percent of waits for WRITES to rollback segmants, and also the percent of waits for READS from rollback segments. If there are too many waits he suggests adding additional rollback segments.

My problem is the book says waits become significant if they happen more than 0.5% of the time, but in the script he's got a comment that prints out saying add more rollback segments if waits for READS happen more than 5% of the time.

So,
(1) Should I use 0.5% or 5% as a guideline?
(2) Should I focus more on waits for WRITES or READS, or both?

Thanks.

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Author: Greg Moore
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