So yes it is periodic by default (in the millisecond range). However you can wait on any request until it has become durable.
As for replication, people seem to have some hate for that, but the reality is that a journalled system that has failed (any database/operating system) will take a large amount of time to come back up, replay/recover journals etc. Not that useful.
http://www.mongodb.org/display/DOCS/Journaling
So yes it is periodic by default (in the millisecond range). However you can wait on any request until it has become durable.
As for replication, people seem to have some hate for that, but the reality is that a journalled system that has failed (any database/operating system) will take a large amount of time to come back up, replay/recover journals etc. Not that useful.