17. Backing Up and Restoring the Database : Logging System : Logging Facility
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Logging Facility
Each installation has an installation-wide transaction log file that keeps track of all transactions for all users. The installation-wide log file can be distributed among up to sixteen partitions (locations), but the files are treated as one logical file.
With dual logging enabled, the installation has an alternate log file. With dual logging, a media failure on one of the logs does not result in the loss of data or the interruption of service. If one of the log file disks fail, the logging system automatically switches to the other log without interrupting the application.
When log files are properly configured, the use of dual logging has a negligible impact on system performance.
In addition to the installation-wide log file every database has its own wal directory. The wal directory files contain an up-to-date representation of the memory structures required for database recovery.