Understanding Transaction Log Files

Transaction log files are used by Calendar Server to capture all of the additions, modifications and deletions made to the calendar database since the latest snapshot. The transactions are not actually applied to the live database until the log file is closed for writing. The interval parameter specifies how often the old log files are closed and new log files are created.

The log file names consist of a configurable name with a unique number appended to the end.

As the log files are closed, they are ready to be applied to the live database. This happens asynchronously, meaning the creation of log files and the writing of transactions into them is done in “real time”, whereas the program applying the transactions to the database is running independently, without regard to the writing of the transactions into the log files. If the system is very busy, the number of log files awaiting application to the database can rise. When the system has slow periods, the program applying the transactions has time to “catch up” and may actually sit idle, waiting for the next transaction log.

After the transactions have been applied to the live database, they are applied to the hot backup snapshot (if enabled). The log files are also written to the same archive directory where the snapshot resides.