Log manager data records
The format of the log manager statistics record is described in assembler macro thlqual.SCSQMACS(CSQDQJST).
In the statistics, these counts are important:
- The total number of log write requests:
Nlogwrite = QJSTWRW + QJSTWRNW + QJSTWRF- The total number of log read requests:
Nlogread = QJSTRBUF + QJSTRACT + QJSTRARH
The problem symptoms that can be examined using log manager statistics are described in Table 17.
Table 17. Problem symptoms that can be examined using log manager statistics
- Symptom 1
- QJSTWTB is nonzero.
- Reason
- Tasks are being suspended while the in-storage buffer is being written to the active log.
There might be problems writing to the active log.
The OUTBUFF parameter within CSQ6LOGP is too small.
- Action
- Investigate the problems writing to the active log.
Increase the value of the OUTBUFF parameter within CSQ6LOGP.
- Symptom 2
- The ratio:
QJSTWTL/Nlogread is greater than 1%.
- Reason
- Log reads were initiated that had to read from an archive log, but WebSphere MQ could not allocate a data set because MAXRTU data sets were already allocated.
- Action
- Increase MAXRTU.
- Symptom 3
- The ratio:
QJSTRARH/Nlogread is larger than normal.
- Reason
- Most log read requests should come from the output buffer or the active log. To satisfy requests for back out, unit-of-recovery records are read from the in-storage buffer, the active log, and the archived logs.
A long-running unit of recovery, extending over a period of many minutes, might have log records spread across many different logs. This degrades performance because extra work has to be done to recover the log records.
- Action
- Change the application to reduce the length of a unit of recovery. Also, consider increasing the size of the active log to reduce the possibility of a single unit of recovery being spread out over more than one log.
- Other pointers
- The ratio
Nlogread/Nlogwrite gives an indication of how much work has to be backed out.
- Symptom 4
- QJSTLLCP is more than 10 an hour.
- Reason
- On a busy system you would expect to see typically 10 checkpoints an hour. If the QJSTLLCP value is larger than this, it indicates a problem in the setup of the queue manager.
The most likely reason for this is that the LOGLOAD parameter in CSQ6SYSP is too small. The other event that causes a checkpoint is when an active log fills up and switches to the next active log data set. If your logs are too small, this can cause frequent checkpoints.
- Action
- Increase the LOGLOAD parameter, or increase the size of your log data sets as required.