Re: rollback segments, why two extents?

Strictly the point is that a transaction will not extend itself from the end of one extent into the beginning of another extent that contains an active transaction, even though a transaction may start in an extent which already contains many active transactions.

This is related to the need to maximise the opportunity for maintaining the option for read-consistency whilst keeping track of the head and tail of the rollback usage.

--

Jonathan Lewis
Yet another Oracle-related web site: www.jlcomp.demon.co.uk

John Higgins wrote in message <372D16E0.69CABD28_at_deere.com>...
>No, many transactions can share a rollback extent. It is at the block
>level that no sharing occurs.
>
>The two extents minimum has to do with the fact that Oracle needs at least
>two active extents whenever a wraparound occurs.
>
Received on Mon May 03 1999 - 02:28:25 CDT