On 2/24/2016 10:08 AM, Stephen Chrzanowski wrote: > IMO, all that, plus the fact that you have an easy roll back mechanism. > Anything that needs to be put in the database is external to the pristine > database. Lock the database with a transaction, fill up the journal, the > power goes out, your pristine database isn't touched.
Rollback journal works the other way round. New data is written to database file; previous content of overwritten pages is copied to journal file. Committing a transaction is fast - simply delete the journal. Rolling back (e.g. after power failure) means copying original pages from the journal back to the database file. In the world you describe - how would you implement committing a transaction? At some point, something must write to the database file; at that point, the file is no longer "pristine". What happens if power goes out in the middle of this? Note also that a typical application commits much more often than it rolls back, so the system should be designed to make the former fast; the latter can be slow. -- Igor Tandetnik
