Re: Do I really need more than 1 rollback segment?

Jonathan Lewis doodled thusly:
>your rollback segment size has to be large
>enough to allow the single longest event
>that requires consistent reads to complete
>at its worst possible run time.

Yup. That's how I arrived at the 400M size. Left it much smaller, then watched how much they growed in heavy batch use. 4 peaked at 400M. 4 being the number of concurrent batch jobs we allow.

>from 25MB minimum size to 400MB is
>an over-reaction that is causing redundant
>I/O to take place - but if you can't see any
>side-effects on the I/O subsystem. who cares ?

Exactly. :-)

>
>You MAY want to experiment with reducing
>the rollback segment size to see if this improves
>the I/O load on the system.

will do. Thanks.

>in which case you MAY reduce the total
>rollback segment volume by reducing the
>number of rollback segments - at which point
>Howard's observation kicks in: if you have too
>few rollback segments you start to see contention
>for the rollback segment header block (the GETS
>reported in v$rollstat start colliding, so the WAITS
>count starts to climb).
>

Yeah. Currently collecting stats to see if I can reduce their number/size. But not too worried: I've got disk space and I/O capacity coming out of my gills in this site! Might as well use it for good measure and get rid of those annoying 1555's once and for all.

Starting to move them to 8.1.7 from 8.0.6 during the Xmas break as well. Wish me luck.

Cheers
Nuno Souto
nsouto_at_optushome.com.au.nospam Received on Thu Dec 20 2001 - 06:13:19 CST