The amount of disk space required depends on the sizes of segments and pages that constitute RDAREAs. You should take this point into account when designing RDAREAs. Table 14-1 lists the items to be examined during RDAREA design, and Table 14-2 lists the maximum and minimum values for RDAREAs.
Table 14-1 Items to be examined during RDAREA design
Design task and items to be examined | Advantages | Disadvantages | Section | |
---|---|---|---|---|
Segment size | Size increased | If a row length changes as a result of update processing or if a row is added to a table for which a cluster key is specified, unused pages can be allocated that are adjacent to the page containing the specified row, thereby reducing the data input/output time. | Because the number of segments is reduced, the number of tables and indexes that can be stored per user RDAREA is also reduced. | 14.2.1 |
Size reduced | If many tables, each of which contains a small amount of data, are stored in one user RDAREA, wasted space caused by unused pages can be minimized. |
| ||
Per-cent-age of free space in segment | Specified | When data is added to a table for which a cluster key is specified, data can be stored in the page close to the cluster key value, thereby reducing the number of data input/output operations. | As the value becomes larger, more disk space is required. | 14.2.2 |
Set to 0 | The disk space required can be reduced. | When data is added to a table for which a cluster key is specified, data cannot be stored in the page close to the cluster key value, resulting in poor storage status; therefore, reduction in the number of data input/output operations is no longer beneficial. | ||
Page length | Percent-age of unused space in page specified |
| For a table with the FIX attribute, storage efficiency is poor. | 14.3.2 |
Percent-age of unused space in page set to 0 | For a table with the FIX attribute, storage efficiency is improved if the data is placed in ascending order. | If a row becomes longer than before as a result of update processing, the row spans multiple pages, resulting in overhead in row accesses. | ||
Free space reusage | Used |
| If there is insufficient free space for reuse, the overhead for free space search increases. | 14.5 |
Not used | If there is adequate free space, rapid insertion processing is possible. | RDAREA storage efficiency is reduced. Performance of free space search after the RDAREA is full is degraded. | ||
Shared RDAREA | Used | If a heavily accessed table that is difficult to partition is stored in a shared RDAREA, the efficiency of parallel processing improves because the table can be referenced by all back-end servers. | When a shared table is updated, the shared RDAREA containing the table is locked, and deadlock may occur if an application accesses another table in the shared RDAREA. | 14.6 |
Not used | Deadlock and server-to-server global deadlock, which sometimes result from use of a shared RDAREA, are avoided. | For complex search processing, such as join processing, overhead associated with connection establishment between multiple back-end servers and with data transfer increases. | ||
Temporary table RDAREA | Used | Temporary tables can be used to perform complex data processing, as well as for executing transactions and SQL sessions without being affected by other users. Temporary tables do not require postprocessing. | There is overhead for initializing a temporary table RDAREA when HiRDB starts or when the first INSERT statement is executed on a temporary table. | 14.7 |
Not used | There is no overhead for initializing temporary table RDAREAs when HiRDB starts. | When intermediate processing results are stored in a table during complex processing, postprocessing is required (such as deleting data after completion of processing). |
Table 14-2 Maximum and minimum values for RDAREAs
Item | Maximum and minimum values |
---|---|
Total number of RDAREAs | 3 to 8,388,592 |
Number of master directory RDAREAs | 1 |
Number of data directory RDAREAs | 1 |
Number of data dictionary RDAREAs | 1 to 41 |
Number of user RDAREAs | 1 to 8,388,589 |
Number of data dictionary LOB RDAREAs | 1 to 2 |
Number of user LOB RDAREAs | 0 to 8,388,325 |
Number of registry RDAREAs | 0 to 1 |
Number of registry LOB RDAREAs | 0 to 1 |
Number of list RDAREAs | 0 to 8,388,588 |
Number of HiRDB files per RDAREA | 1 to 16 |
Number of base tables per RDAREA | 0 to 500 |
Number of indexes per RDAREA | 0 to 500 |
Number of lists per RDAREA | 0 to 50,000 |
Total number of HiRDB files | 1 to 134,217,728 |