oracle redo log transaction

hi,
i've read the guides from oracle but don't understand fully how redo logs works exactly.
i'm coming from sqlserver world and i know i can't make a comparaison but ...

I know that when a redolog is full, the LGWR do a log switch but what occrurs when a log are switched ?
LGWR call DBWR to applies change from the current redolog (which will be switched) to the datafiles or/and the rollback segment ? then DBWR notifes LGWR that it can resume ?

Now after the second log switch the first redo log will be rewritten and if i issue a rollback, from
where the data are taken to rollback? from the rollback segment ? what process write to the rollback segment ? And if the DB crash, since the statement is not finished there will be a rollback ?

why from a performance view, no one recommend a important redolog size ? > 50 Mo and onl 3 to 5 files ?

Let's take a update statement on a big table (10 millions rows), if i have only 2 redo logs about 10 Mo each.
How oracle does not return an error that redolog is full (like in mssql) ? is this the size of the rollback segment who actually limit the size of the transaction ?

thx
tom (apologies for my english) Received on Fri Nov 12 2004 - 04:06:27 CST