Beginning with V13, an online file compact feature is available.
Online Compact allows for physical reorganization of the records within data files in order to eliminate unused space. It also provides a means to migrate all records to the newest schema version following one or more Hot Alter Table operations. The file may be actively in use by other users while this compact takes place. On completion, the file size is reduced which returns extra space to the file system. Additionally, if the file is under full transaction control, the indexes are then automatically rebuilt using Online Rebuild.
Online Rebuild allows for an index rebuild to occur on ctTRNLOG files while the file is actively in use by other users. This can reduce index file system usage, and generate more optimized indexes. It can also be used to change the index from a smaller PAGE_SIZE to a larger one.
Online Compact and Online Rebuild operations are generally slower than the exclusive compact and rebuild versions, but can take place in the background allowing for continuous file access. However, applications may encounter issues such as locking errors due to interaction from these operations.
NOTE: When the online compact is run on a file that uses the hot alter feature (also known as FLEXREC) which permits the record schema to be quickly updated, all the records are updated to the current schema definition.