This parameter determines the frequency of soft checkpoints and the recovery range, which help out in the crash recovery process.
The softmax parameter is replaced with the new page_age_trgt_mcr and page_age_trgt_gcr parameters, which are both configured as a number of seconds.
Existing upgraded databases continue to use the softmax parameter. You can check if you are using softmax by querying the database configuration and checking the value of this parameter. You can switch from using softmax to these new parameters by setting the value of softmax to 0.
New databases are created with the value of softmax set to 0 by default.
To influence the number of log files required for crash recovery, the database manager uses this parameter to trigger the page cleaners to ensure that pages older than the specified recovery window are already written to disk.
To determine which records from the log file need to be applied to the database, the database manager uses information recorded in a log control file. (The database manager actually maintains two copies of the log control file, SQLOGCTL.LFH.1 and SQLOGCTL.LFH.2, so that if one copy is damaged, the database manager can still use the other copy.) These log control files are periodically written to disk, and, depending on the frequency of this event, the database manager might be applying log records of committed transactions or applying log records that describe changes that have already been written from the buffer pool to disk. These log records have no impact on the database, but applying them introduces some additional processing time into the database restart process.
The log control files are always written to disk when a log file is full, and during soft checkpoints. You can use this configuration parameter to control the frequency of soft checkpoints.
( (space between recorded and current states) / logfilsiz ) * 100
Recommendation: You might want to increase or reduce the value of this parameter, depending on whether your acceptable recovery window is greater than or less than one log file. Lowering the value of this parameter will cause the database manager both to trigger the page cleaners more often and to take more frequent soft checkpoints. These actions can reduce both the number of log records that need to be processed and the number of redundant log records that are processed during crash recovery.
In both of these cases, the log control information kept in memory does not change frequently and there is no advantage in writing the log control information to disk, unless it has changed.