Logging and checkpoints
The parameters affecting the performance of logging are spread across two PROCLIB members, PB and VSAM.
- DFSPBxxx
- CPLOG
- WADS
- DFSVSMxx
- WADSDEF
- OLDSDEF
IRUR: Logger Statistics
The Logger Statistics report is one of the Internal Resource Utilization reports (IRUR) and provides various statistics describing the performance of the IMS log and write-ahead data set (WADS).
I/O counts and Buffer Wait counts can be used to see if any performance problems are being caused by bad logger or WADS I/O times.
Logger Statistics Interval : 20.00 (HHHH.MM.SS)
Count /Transact /Second
Logical Logger: Records written 212,075 24.18 176.73
Check write requests 15,400 1.76 12.83
Waits for writes 20 .00 .02
Buffer waits: chkpt invokers 8 .00 .01
Buffer waits: non-chkpt invokers 1 .00 .00
Awe submitted on wrt 0 .00 .00
Physical Logger: WADS EXCPVRs 8,607 .98 7.17
2K segment writes initiated 24,482 2.79 20.40
OLDS writes initiated 1,766 .20 1.47
OLDS reads initiated 2 .00 .00
Internal checkpoint requests 6 .00 .00
Accumulative wtwt wait time 2,125 .24 1.77 A key performance indicator is the number of Logical Logger Buffer waits for non-checkpoint invokers. A high value might indicate that the Log Buffer allocation might be too low.
System Checkpoint report
The second part of the System Checkpoint report summarizes checkpoint activity, including:
- Average checkpoint duration and frequency
- Record counts by subtype
The following figure shows an example of a Checkpoint Summary report.
Start 21Jan2018 11.49.45.70 IMS Performance Analyzer End 21Jan2018 12.58.45.16 Page 111
Checkpoint Summary - PROD
Completed Checkpoints = 7
Average Checkpoint Duration = 0.204 (hhhh.mm.ss.ths)
Average Checkpoint Frequency = 11.29.713 (hhhh.mm.ss.ths)
CPLOG = 46613
Checkpoint Start: 21Jan2018 12:58:45:16 End: 21Jan2018 12:58:45:41 Number : 117
Subtype Description Count Bytes %Total
_______ _______________________________________ __________ __________ ______
01 Begin Checkpoint 1 1,504 0.24
03 CNT - Communication Name (Node) Table 2 6,064 0.49
04 SMB - Scheduler Message Block 173 685,128 42.09
05 CTB - Communication Terminal Block 1 3,488 0.24
06 DDIR - DMB Directory Entry 50 50,080 12.17
07 PDIR - PSB Directory Entry 82 83,720 19.95
08 CLB - Communication Line Block 1 192 0.24
0D CCB - Conversational Control Block 1 1,376 0.24
0F LCB - Link Control Block 1 176 0.24
10 CRB - Communication Restart Block 1 352 0.24
14 SPQB - Subpool Queue Block 16 60,636 3.89
21 VTCB - VTAM Terminal Control Block 8 30,796 1.95
22 Queue Anchor block (LU 6.2) 1 32 0.24
30 RRE - Residual Recovery Element 6 5,330 1.46
31 SIDX - Subsystem Index Entry 1 132 0.24
32 OTMA TPIPES/QABS 1 240 0.24
33 OTMA MTES/MCBS 1 248 0.24
80 Fast Path Begin Checkpoint 1 307 0.24
83 RCTE - Routing Code Table Entry 1 56 0.24
84 DMCB - DEDB Master Control Block 49 32,396 11.92
86 DMHR - Fast Path Buffer Header 3 13,176 0.73
87 ADSC - Area Data Set Control Block 8 7,696 1.95
89 Fast Path End Checkpoint 1 52 0.24
98 End Checkpoint 1 40 0.24
_______ _______________________________________ __________ __________ ______
TOTAL 411 983,217 100.00 A Checkpoint Summary report is produced for each IMS Subsystem ID and contains the following information:
- Completed Checkpoints
- Number of completed checkpoints found in the log file. A complete checkpoint is one that starts with a 4001 record and ends with a 4098 record.
- Average Checkpoint Duration
- The average elapsed time per checkpoint in the format hhhh.mm.ss.ths.
If there are insufficient completed checkpoints to allow a meaningful calculation, the following message is printed:
Insufficient Checkpoints to calculate. - Average Checkpoint Frequency
- The average time between checkpoints, or how frequently checkpoints are taken, in the format
hhhh.mm.ss.ths.
If there are insufficient completed checkpoints to allow a meaningful calculation, the following message is printed:
Insufficient Checkpoints to calculate. - CPLOG
- Checkpoint frequency. The average number of log records written between checkpoints.
- Checkpoint
-
- Start:
- Checkpoint start date and time.
- End:
- Checkpoint end date and time.
- Number:
- Checkpoint number.
- Subtype
- Checkpoint record subtype.
- Description
- Subtype description.
- Count
- Total number of checkpoint records of this subtype.
- Bytes
- Total bytes of checkpoint records of this subtype.
- %Total
- Percentage of records of this subtype over all checkpoint records.
- Total
- Count
- Total number of records in the checkpoint.
- Bytes
- Total number of bytes of all records in the checkpoint.
- %Total
- Should always be 100.00.