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Nonstop Database, HiRDB Version 9 System Operation Guide
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Job tasks that repeatedly insert or delete rows in a table reduce the storage efficiency of tables or indexes and become a factor in reducing performance. Therefore, you must regularly use the database reorganization utility to reorganize tables or indexes. However, you must stop job tasks that access the table to be reorganized because that table or index cannot be accessed by other UAPs or by utilities while the database reorganization utility is executing. If job tasks cannot be stopped or indexes cannot be reorganized, you can use the following facilities:
Releasing used free pages and used free segments makes it possible to reuse those free pages and segments. Using the free space reusage facility makes it possible to reuse the free space in a page. Combining these facilities makes it possible to increase the time between reorganizations of tables and indexes because data storage efficiency in increased and performance degradation is minimized.
When you delete a large amount of table data, such as with a batch job for example, there are cases where some of the pages (data pages) storing that table data become used free pages. Also, if you have defined an index, some of the pages (index pages) storing the index key values become used free pages. Executing the free page release utility (pdreclaim command) makes it possible to change these used free pages into unused pages which can then be reused. This is called releasing used free pages. You can also reuse used free segments by turning them into unused segments. This is called releasing used free segments.
For details about releasing used free pages and used free segments, see 15.11 Re-using used free pages and used free segments.
If data cannot be stored within a segment using INSERT or UPDATE processing, data is stored in a free area within a used segment (a free area in a page) without allocating a new unused segment. This is called the free space reusage facility. Using this facility makes it possible to reuse free areas that became unavailable when data was deleted.
To use the free space reusage facility, specify SEGMENT REUSE when you execute CREATE TABLE. For details about the free space reusage facility, see the HiRDB Version 9 Installation and Design Guide.
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