Re: rollback after crash

"Pradeep" <agarwalp_at_eeism.com> wrote in message news:1134578650.960249.62470_at_z14g2000cwz.googlegroups.com...
> Thanks lewis your reply was great and easy to understand. One question
> on smon & pmon. Below is from Expert oe-on one
>
> for PMON "If your dedicated server 'fails' PMON will rollback
> uncommited work"
> for SMON " SMON responsible for peforming crash recovery of a failed
> instance upon restart"
>
> And this is what confuses me between PMON & SMON. Please can you
> clarify?
>

All Oracle processes are the same on-disc code, so any process could run any bit of the code - in theory - so it's perfectly feasible for smon and pmon both to have the ability to perform a rollback of a transaction that has no parent.

smon happens to do this only at system recovery, when there may be lots of dead transactions and you don't want pmon to be tied up for a long time.

pmon does this whenever it finds a dead process - which isn't very often (you hope).

Smon wakes up every 5 minutes to do all sorts of things; pmon wakes up every 3 seconds to do a check for dead processes. The different time-scales explain why it is smon that does the rollbacks on recovery and pmon does it only in normal running.

-- 
Regards

Jonathan Lewis

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