Instance recovery behaviour

[pando]

well not only redo is read during instance recovery, RBS are read as well

imagine I have an uncommitted transaction in redo log 1 and I have 3 redo logs, this transaction is recorded in redo log 1, then several transactions are going on, checkpoints are occuring all the time so my uncommitted trsanction is flushed to disk as well since it's dirty block, my redo log 1 gets overwritten, in redo log 2 instance crashes

then in instance recovery Oracle reads Redo logs and RBS and noticed I had an uncommitted transaction so it rolls back my transaction (and hey the redo has been overwritten), so no big deal

what happens with committed transactions? well checkpoints ensure they are flushed to disk, checkpoint occurs all the time and during log switches as well so at the end of the day I only really have to read the last redo log to recover any committed changes and in instance recovery *most* of the time Oracle only reads the last redo log