Oracle database transaction restart

Question

So let's suppose that the system has pending transactions and finished ones. How does the system know during restart which transaction must restart or resume ?

Answer 1

Some Oracle database shutdown modes wait for certain events to occur (such as transactions completing or users disconnecting) before actually bringing down the database. There is a one-hour timeout period for these events. You can see details on the four different shutdown modes (NORMAL, IMMEDIATE, TRANSACTIONAL, ABORT) here: http://docs.oracle.com/cd/B19306_01/server.102/b14231/start.htm#i1006543

Ultimately every transaction either ends in a commit or a roll-back. So if, for example, the server powered down unexpectedly, the database manager process (or service) would handle any uncompleted transactions when the server is restarted (generally by performing a roll-back on them). The details of intermediate progress made on transactions currently in process is stored in database log files (which can generally survive a sudden shutdown). Without these database logs, the database manager would not be able to perform a proper roll-back.