A table can become fragmented after many updates, causing performance to deteriorate. If you collected statistics and did not notice a visible performance improvement, reorganizing table data may help. When you reorganize table data, you are rearranging the data into a physical sequence according to a specified index, and removing the free space that is inherent in fragmented data. This can provide faster access to the data, thereby improving performance.
Before you reorganize tables, it is recommended that you invoke the REORGCHK command, and collect statistics on the table. Running this command will help you determine whether a reorganization of the table data is appropriate. Refer to the Command Reference for information about the REORGCHK command.