Automatic extension is available for the following RDAREAs:

• Data dictionary RDAREAs
• User RDAREAs
• Registry RDAREA
• User LOB RDAREAs
• Data dictionary LOB RDAREA
• Registry LOB RDAREA

Automatic extension is not available for 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.

HiRDB automatically extends an RDAREA when either of the following automatic extension triggers occurs:

• The number of free segments in an RDAREA falls to or below the number of segments to be automatically extended in a single process.
  For example, the number of segments to be automatically extended in a single process is set to 50. If the number of free segments falls to or below 50, automatic extension takes place.
  
• There are no free segments in an RDAREA, and new segments cannot be secured.

Automatic extension triggers can be specified using the pd_rdarea_extension_timing operand. For details, see the manual HiRDB Version 9 System Definition.

We generally recommend method 1 for automatically extending an RDAREA. Because method 1 automatically expands the HiRDB file system area to the maximum size of the HiRDB file (64 GB), it makes it easy to estimate the area size and extend the database.

However, because method 1 is subject to the following restrictions, select method 2 when method 1 cannot be used:

• Only a single HiRDB file can be stored in each HiRDB file system area, and so you must create as many HiRDB file system areas as there are files comprising the RDAREA.
• The HiRDB file system area is automatically extended to 64 GB provided that there is sufficient free space on the disk, and so you cannot set a maximum size for disk usage.

When you perform automatic extension of an RDAREA, monitor the size of the following items:

• Size of the HiRDB file system area
• Free space on the disk on which the HiRDB file system area was created

Especially if you are using method 1, you must monitor the free space because you cannot set a maximum size for disk usage.

Additionally, we recommend that you reorganize the tables and indexes in the RDAREAs to prevent RDAREAs and HiRDB file system areas from becoming unnecessarily large. You can specify the pd_rdarea_warning_point operand to monitor the HiRDB file usage rate and extent count and issue a warning message. In this way, you can take the necessary action before automatic extension becomes impossible. For details about the pd_rdarea_warning_point operand, see the manual HiRDB Version 9 System Definition.

When size cannot be monitored

When size cannot be monitored, a space shortage in the HiRDB file system area or disk might cause an error shutdown if a space shortage occurs during RDAREA automatic extension. Therefore, either do not apply RDAREA automatic extension, or use a setting that initializes the area to be extended during automatic extension if any of the following conditions applies:

• A method that automatically expands the HiRDB file system area is used.
• The HiRDB file system area of an RDAREA is created in a regular file.

For details about how to initialize an area during automatic extension, see 15.8.3(2) Initializing a HiRDB file system area to be expanded during automatic extension.

Reference note

Relationship between RDAREAs and extents

An extent is a group of contiguous areas inside the HiRDB file system area. The following figure illustrates extents.

The maximum number of extents that a single HiRDB file can hold is 24. During automatic extension, if a free space is secured that is contiguous to the last allocated extent of the target HiRDB file, the number of extents is not increased. However, if non-contiguous free spaces are allocated, the number of extents increases. For example, in the above figure, the number of extents in HiRDB file A is 2. Extent information can be checked with the pdfls command.

When an RDAREA is deleted, re-initialized (assigned size reduction or with reconstruction operand), or consolidated, the assigned extents are deleted or their size is reduced. This causes fragmentation in the HiRDB file system area. Note that if an RDAREA is added, extended, or re-initialized from this state, multiple extents might be assigned to a single HiRDB file even without automatic extension.