15.7.1 Automatic extension of an RDAREA

When a space shortage occurs in an RDAREA, the size of the RDAREA can be expanded by means of automatic addition of segments, provided that there is sufficient free space in the HiRDB file system area. This process is called RDAREA automatic extension. Figure 15-1 illustrates RDAREA automatic extension.

Figure 15-1 RDAREA automatic extension

[Figure]

A contiguous area in a HiRDB file system area is called an extent. The maximum number of extents in a HiRDB file is 24. During automatic extension, if contiguous free space can be allocated following the last allocated extent of the target HiRDB file, the number of extents does not increase. However, if non-contiguous free space is allocated, the number of extents increases. Extent information can be checked with the pdfls command.

When RDAREAs are deleted, reinitialized (allocated size is reduced or with reconstruction is specified), or combined, allocated extents are deleted or their sizes are reduced, as a result creating fragmented free spaces within the HiRDB file system. Note that if RDAREAs are added, expanded, or reinitialized in this state, multiple extents may be allocated to a single HiRDB file even if automatic extension is not executed.

Organization of this subsection
(1) RDAREAs eligible for automatic extension
(2) Setting automatic extension
(3) Notes

(1) RDAREAs eligible for automatic extension

Automatic extension can be applied to the following RDAREAs:

(2) Setting automatic extension

The following is the procedure for setting automatic extension:

Procedure
To set the automatic extension:
  1. When the HiRDB file system area is created with the pdfmkfs command, specify the maximum number of extensions (in the -e option).
  2. When an RDAREA is created, use a utility control statement* to specify use of the automatic extension facility.
* This can be specified in the CREATE RDAREA, EXPAND RDAREA, INITIALIZE RDAREA, or ALTER RDAREA statement of the database initialization utility, database structure modification utility, or registry facility initialization utility.

(3) Notes

  1. Automatic extension cannot be applied to an RDAREA that stores an abstract data type provided by a plug-in. However, in the case of the HiRDB Text Search Plug-in with the SGMLTEXT type, a portion of the index management area can be extended automatically.
  2. If automatic extension is not possible because of a space shortage in the HiRDB file system area, you must either extend the RDAREA or reorganize the tables or indexes in the RDAREA.
  3. If the number of extents exceeds the maximum, which is 24, you must either consolidate the extents in the HiRDB file system area into a single extent or extend the RDAREA. To consolidate extents in a HiRDB file system area, first make a backup of the HiRDB file system area with the pdfbkup command, then initialize the HiRDB file system area with the pdfmkfs command. You can then use the pdfrstr command to restore the HiRDB file system area.
  4. While an RDAREA is in updatable backup hold status or updatable backup hold (WAIT mode) status, RDAREA automatic extension is suppressed. For this reason, you should refrain, while an RDAREA is in either of theses statuses, from executing a job that adds or updates a large volume of data, thus requiring allocation of new pages. To release suppression of RDAREA automatic extension, use the pdrels command to release the RDAREA from the hold.
  5. When the hybrid method is used in Real Time SAN Replication, HiRDB waits for the database to be synchronized with the remote site when RDAREA automatic extension occurs. For this reason, an extension operation my result in a processing overhead of 2 seconds or longer.