- 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.
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- 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.
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- 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.
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- 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.
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