OpenEdge supports one or more after-image extents per database when after-imaging is enabled. Each extent of the after-image file is its own area with a unique area number, but it is more common to refer to them as extents. You need more than one extent for each after-image file to support a high-availability environment.
Each extent has five possible states. They are:
Empty — An extent that is empty and ready for use.
Busy — The extent that is currently active. There can only be one busy extent per database.
Full — An extent that is closed and contains notes. A full extent cannot be written to until the extent is marked as empty and readied for reuse.
Locked — An extent that is full and has not been replicated by OpenEdge Replication. You will only see this state when you have OpenEdge Replication enabled.
Archived — An extent that is full and has been archived by AI File Management, but has not been replicated by OpenEdge Replication. You will only see this state when AI File Management and OpenEdge Replication are enabled.
Multiple extents allow you to support an online backup of your database. When an online backup is executed the following occurs:
1. A latch is established in shared memory to ensure that no update activities take place.
2. The modified buffers in memory are written (pseudo-checkpoint).
3. An after-image extent switch occurs (if applicable).
4. The busy after-image extent is marked as full, and the next empty extent becomes the busy extent.
5. The primary recovery area is backed up.
6. The latch that was established at the start of the process is released.
7. The database blocks are backed up until complete.
Empty — An extent that is empty and ready for use.