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Database Essentials
Administrative Planning : Database areas : Primary recovery (before-image) information : Extent size rules
Extent size rules
These rules apply to both the primary recovery area and the data areas:
*Do not make them too large
*Always make the last extent variable length
*Enable large files as a safety valve
Enabling large files is particularly important on file system that holds the primary recovery area because this is the place most likely to experience issues. A large update program with poor transaction scoping or a transaction held open by the application for a long period of time can cause abnormal growth of this area. If the fixed portion of an area is 2GB in size, you start extending your variable portion in that same transaction. Only then do you notice that you might need more than 2GB of recovery area to undo the transaction. If you are large-file enabled and have enough disk space, there is no problem. If you are not large-file enabled, the database might crash and not be recoverable because there is no way to extend the amount of space for the recovery area without going through a proper shutdown of the database.