Overview of the Online/Defrag feature
No function has been able to reorganize a database while the database remains online and available for updates—until now.
Online/Defrag provides increased availability and performance for IMS databases that require continuous or near-continuous availability. Online/Defrag can reorganize a single database record or an entire database with
- No down time
- Minimal user interaction
- Concurrent updates
Online/Defrag provides reorganization functions for HDAM, HIDAM, PHDAM, and PHIDAM databases that are experiencing performance problems caused by record fragmentation. Online/Defrag offers an analysis component that lets you target a reorganization to only those areas within the database that need to be reorganized. Moreover, Online/Defrag recommends the reorganization parameters that will reduce I/O activity the most.
Online/Defrag does not replace existing BMC reorganization utilities because those utilities are still needed for reorganizations that require database description (DBD) or space allocation changes. Online/Defrag complements the existing reorganization utilities to provide a comprehensive end-to-end reorganization solution for IMS full-function databases.
The Online/Defrag job schedules a batch message processing (BMP) program to communicate with DBCTL. The process by which the database is reorganized is dependent on the specified mode. Online/Defrag offers the following reorganization modes:
- Record
Online/Defrag reorganizes only those records that are recommended for reorganization by the Online/Defrag Record Analysis. - Scan
Online/Defrag analyzes every record in the database and reorganizes only those records that meet specified criteria. - Block
Online/Defrag reorganizes every record in the database. No analysis is performed to determine the fragmentation level of the records.
During initialization, Online/Defrag identifies blocks that have a user-defined amount of free space. Blocks are identified as free or full. The free blocks are reserved for use as reorganization targets. There must be enough free space in the database to reorganize the largest record. A record might be skipped if not enough target blocks are available to contain it.
Block status (free or full) is continuously updated throughout the reorganization process. Blocks that were previously free might become full; blocks that were previously full become free when they meet the user-defined amount of free space. The status is dynamic because of the movement of records during the reorganization.
Online/Defrag lets you interrupt a reorganization and then resume the same job. When the job is interrupted, Online/Defrag stores the key value of the restart record for use when the reorganization is restarted. For more information about interrupting and resuming a reorganization, see RESUME.
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