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Achieving specific recovery targets
Use this topic for guidance on how you can achieve specific recovery target times by adjusting backup frequency.
Formula (A)
Required restart time * System recovery log read rate
(in secs) (in MB/sec)
Backup frequency = -----------------------------------------------------
(in hours) Application log write rate (in MB/hour)
For example, consider a system in which IBM MQ MQI clients generate a total load of 100 persistent messages a second. In this case, all messages are generated locally.
100 * (1 + 1.3) KB * 3600 = approximately 800 MB
where
100 = the message rate a second
(1 + 1.3) KB = the amount of data logged for
each 1 KB of persistent messages
3600 seconds * 2.7 MB a second / 800 MB an hour = 12.15 hours
If your IBM MQ application day lasts approximately 12 hours, one backup each day is appropriate. However, if the application day lasts 24 hours, two backups each day is more appropriate.
Another example might be a production system in which all the messages are for request-reply applications (that is, a persistent message is received on a receiver channel and a persistent reply message is generated and sent down a sender channel).
50((2 * (1+1.3) KB) + 1.4 KB + 2.5 KB) * 3600 = approximately 1500 MB
where:
50 = the message pair rate a second
(2 * (1 + 1.3) KB) = the amount of data logged for each message pair
1.4 KB = the overhead for each batch of messages
received by each channel
2.5 KB = the overhead for each batch of messages sent
by each channel
1800 seconds * 2.7 MB a second / 1500 MB an hour = 3.24 hours
Periodic review of backup frequency
Monitor your IBM MQ log usage in terms of MB an hour. Periodically perform this check and amend your page set backup frequency if necessary.