10.12.2 Trigger for reducing the size of the system log files
As a database is updated, system logs are output, which increases the size of system log files. Especially, when a database is massively updated (for example, by an unscheduled operation), the size of some user log files might increase considerably. A problem, such as DB directory suppression, might occur as a result. To prevent the size of the DB directory from being suppressed, the HADB server automatically reduces the size of system log files triggered by the following conditions.
- Trigger for reducing the size of the master log file
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If the size of the master log file is larger than 2 megabytes when the transaction that updated the database was settled, the size of the master log file is reduced. However, if either of the following conditions is satisfied, the processing of reducing the size of the master log file is skipped because the system logs being used exist in the master log file:
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Another transaction that updates the database exists.
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The transaction that caused processing to reduce master log file size is running processing to delete data in the archive directory.
- Important
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If multiple transactions that update the database continue running, processing to reduce master log file size is not executed. Therefore, we recommend that you regularly (for example, once a day) and intentionally set the time period during which update transactions are not concurrently executed.
- Note
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If you execute the following SQL statements or command for the archivable multi-chunk table, the processing for deleting data in the archive directory is executed:
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DROP SCHEMA statement
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REVOKE statement with SCHEMA specified
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DROP TABLE statement
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TRUNCATE TABLE statement
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ALTER TABLE statement (when executed to change an archivable multi-chunk table to a regular multi-chunk table)
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PURGE CHUNK statement
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adbunarchivechunk command
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- Trigger for reducing the size of user log files
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When the update transaction was settled, the size of a user log file used by that update transaction might be larger than the size specified (as the trigger value for reducing the size of user log files) in the adb_log_usrfile_size operand in the server definition. In this case, the size of the user log file is reduced to the initial size#.
- #
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This is the size specified as the initial size of user log files in the adb_log_usrfile_size operand.
Consider the following related to reduction of user log file size.
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To prevent the impact (on update performance) of processing to reduce user log file size:
If there is enough free space on the disk, in the adb_log_usrfile_size operand, specify 0 as the trigger value for reducing user log file size. If 0 is specified, processing to reduce user log file size is not performed.
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To prevent a shortage of disk space due to increased user log file size:
Omit specifying the adb_log_usrfile_size operand. Alternatively, in the adb_log_usrfile_size operand, specify a value other than 0 for the trigger value for reducing user log file size. In this case, processing to reduce user log file size is performed. However, during normal operation, an increased number of processes for reducing user log file size might impact update performance. Therefore, regularly check the number of processes for reducing user log file size. For details about how to check the number of processes for reducing user log file size, see 13.1.9 Re-evaluating the trigger size for reducing user log files.