When system log files need to be swapped, HiRDB (the unit) will terminate abnormally if there are no swappable target system log files. To prevent this, HiRDB has a facility for monitoring the free space remaining for system log files (monitoring free area for system log files facility). This facility operates when the percentage of available free area for the system log files reaches a warning value. Select one of the following two levels.
If level 2 is selected, all transactions in the server are terminated forcibly when there becomes insufficient free space in the system log files. Because of the severity of this action, the system log files should be designed quite carefully.
The following explains some of the design considerations for system log files.
Size of one system log file (bytes) ![]() ![]() ![]() ![]() |
System log file total size (bytes) ![]() |
If the total size of the system log files is unchanged, the size of each generation will depend on how many generations of system log files are being maintained. The following table describes the effect on operations of the number of generations of system log files. The total size of the system log files is unchanged.
Table 9-5 Effects on operations of the number of generations of system log files
Comparison item | System log file configuration | |
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Small number of generations | Large number of generations | |
Size of each generation of system log files | Becomes larger. | Becomes smaller. |
Swap interval | Because the size of each generation of system log files becomes larger, the swap interval becomes longer. | Because the size of each generation of system log files becomes smaller, the swap interval becomes shorter. |
Unload frequency | Because the swap interval becomes longer, the unload frequency becomes lower. | Because the swap interval becomes shorter, the unload frequency becomes higher. |
Effects on the system log size when something such as a disk failure makes several generations of system log files unusable |
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In normal operations, the lower the number of generations of system log files, the more advantageous the swapping interval and the unload frequency will become. However, if there is a failure, the effects on operations will be reduced with a larger number of log file generations.
When system log file duplexing is used, HiRDB acquires the same system log information in both versions. In the event of an error on one of the versions, the system log can be read from the other version, thereby improving system reliability. When dual system log files are used, they must be used under the management of HiRDB rather than using a mirror disk. When using dual system log files, create the files for each system on a separate hard disk.
To use dual system log files, specify the following operands in the server definition:
Single operation of system log files is employed when dual system log files are used.
In the event of an error in a system log file, processing can continue using the normal version of the system log file without having to terminate the HiRDB unit abnormally even if neither system has a usable system log file. This is called single operation of system log files. To perform single operation of system log files, specify pd_log_singleoperation=Y in the server definition.
As opposed to single operation of system log files, continuing processing using both versions of system log files (normal processing mode) is called double operation of system log files
If there is no overwrite-enabled system log file at the time of a HiRDB restart, but a reserved file is available, then HiRDB continues processing by opening the reserved file and placing it in overwrite-enabled status. This is called automatic opening of system log files.
To perform automatic opening of system log files, specify pd_log_rerun_reserved_file_open=Y in the server definition.
Use the pdloginit command's -l option to specify the record length of a system log file. You can select 1,024, 2,048, or 4,096 as the record length.
When you are constructing a new HiRDB, we recommend that you select 1,024 as the record length, because this will improve system log storage efficiency. To do this, specify a value of 1024 in the pd_log_rec_leng operand in the server definition.
If the record length is small, the number of file input/output operations increases for large-sized data. However, file utilization efficiency improves because empty areas created by rounding up to a multiple of the record length are small.
If the record length is large, the number of file input/output operations decreases for large-sized data. However, file utilization efficiency becomes poor because empty areas created by rounding up to a multiple of the record length are large.
If the record length is not 1,024, we recommend that you change it to 1,024 to improve system log storage efficiency.
For details about how to change the system log file record size, see the HiRDB Version 9 System Operation Guide.
The pdlogadfg and pdlogadpf operands are used to define the correspondence between file groups and the created system log files.