Fragmentation occurs naturally when a database is used frequently by adding, deleting, and modifying the data within it.  The more changes occur, the more fragmented the database gets as data becomes scattered through the pag files, and the size of the database becomes inflated.  The index files have to compensate for this, and what starts as a simple map becomes a spaghetti mess. 

If you are unfamiliar with Essbase’s storage method, here is a brief overview.  Essbase has two sets of files related to the data stored in a database.  The numeric data is stored in files with an extension of pag.  Essbase also has files with an ind extension.  These index files are used to store the pointers to the data in the pag files.  As data is requested, Essbase must read the index files to know where the data is located in the pag files.

The result of a more fragmented database can have drastic effects on size and performance.  If you have a database where performance continues to decrease, fragmentation might be the source of the problem.  Performance degradation can occur over weeks or months, but can also occur much more frequently.  Databases with frequent data loads, or updates, can be impacted within a day.

A great way to identify the impact fragmentation is having with a database is to export your data (level 0 in most cases), reload it, and execute the process in question.  By exporting and reloading the data, fragmentation can be completely eliminated.

For more information about pag or ind files, please refer to the database administrator’s guide provided by Oracle.