Re: understanding RBS - Guidelines

Dave,

I think that the following guidelines are not bad and easy to apply:

• Set MINEXTENTS and OPTIMAL so that you have 10 extents per RBS.
• NEVER forget to set OPTIMAL!!!
• select sum(waits)/sum(gets) from v$rollstat; should be less than 1%, otherwise increase nr of RBS (it represents the number of times a transaction had to wait to access the rbs header. If too many tx's go to the same rbs, this value will be high)
• select wraps from v$rollstat; should not increase too often, otherwise take bigger extents.
• select extends, shrinks from v$rollstat; should be close to zero otherwise take bigger extents.
• if select hwmsize from v$rollstat; is big, you either have done a very long transaction, or otherwise take bigger extents.
• If you encounter snapshots too old, increase RBS size, or optimize your long running queries.

The wraps, extends, shrinks and hwmsize mean what you would think they mean.
Know that you can always add/remove rbs while database is up and running.

Greetings from an ex dba-instructor,
Geert

-- 

HIGDON'S LAW:
Good judgement comes from experience, experience comes from bad
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