All operations that affect the “state” of the Queue Manager and its objects are logged to a log file.
What is “state”?
- Object definitions (queue manager, queues, processes, channels, etc)
- Queue content (messages)
Message channel states are logged separately by each channel. There are two forms of Logging
Circular – log records are written sequentially across several files, then “wrap” back to the first file.
log records are written sequentially across files. New files are allocated as current files fill. No automatic reuse of file space!
Problem: Length (in time) of longest running transaction vs amount of writes to log determines size of log needed.
Circular logging is easy to manage, but is fatal if log is damaged (hard to backup circular logs!).
Linear logging is hard to maintain but provides for archiving of previous logs (still a problem if “current” log is damaged).