IMS internal resource usage
There are several summary reports that you can use to examine the level of internal contention for resources.
The following list gives a brief explanation of these reports.
- Pool space failure
- The Pool Space Failure Summary report gives the number of times
in each region a given amount of storage was unavailable. It shows
the number of bytes, the identification of the pool, and the number
of occurrences when storage was unavailable. You can use this summary
to determine if you need to increase the buffer pool allocation, either
by a system definition change or by overriding the number of buffers
in the EXEC statements in the JCL.
The format of the report is shown in the following example.
POOL SPACE FAILURE SUMMARY POOL ID BYTES REQ. OCCURRENCES DLMP 8888 1 DLDP 7777 1 TOTAL 2 - Programs experiencing deadlock
- Each time a pair of programs reaches a deadlock over ownership
of a segment in a given database data set, the Deadlock-Event-Summary
report records the occurrence. Each line in the report shows the two
PSBs involved and indicates which is given processing right-of-way
(REQ-ING PSB) and which has to reprocess after dynamic backout occurs
(LOSING PSB). The report is illustrated in the following example.
DEADLOCK EVENT SUMMARY REQ-ING PSB LOSING PSB DMBNAME OCCURRENCES PSBNAME1 TPPSBRE3 DBASEBAL 1 TOTAL 1 - IMS latch conflict
- The basic serialization of the task processing in IMS is controlled by ownership of an IMS latch. When different programs are executing,
they compete for the ownership. If they wait for the resource, the
one possessing the latch has to post the other ITASK waiting for it.
Use the Latch Conflict Statistics report to judge the level of contention
for a resource.
The latch names, which are abbreviations for the different types of resources being serialized, are as follows:
- Abbreviation
- Latch Name
- DISP
- SYS/DISPATCHER
- DCSL
- DC/CHECKPOINT DC SYSTEM
- LUML
- DC/LU 6.2 LUM
- CONV
- DC/CONVERSATION CHECKPT
- TERM
- DC/TERMINAL
- LUBT
- DC/LU62 LUB-TIB CHAIN
- SCHD
- TM/SCHEDULING
- TCTB
- TM/TCT BLOCK
- APSB
- TM/ALLOCATE PSB (BLK MVR)
- PDRB
- TM/PDIR BLOCK (BLK MVR)
- PSBP
- TM/PSB POOL (BLK MVR)
- DMBP
- TM/DMB POOL (BLK MVR)
- PSBB
- TM/PSB BLOCK (BLK MVR)
- DMBB
- TM/DMB BLOCK (BLK MVR)
- PDRP
- TM/PDIR POOL (BLK MVR)
- DBAU
- TM/DBRC AUTH (BLK MVR)
- DDRB
- TM/DDIR BLOCK (BLK MVR)
- DDRP
- TM/DDIR POOL (BLK MVR)
- DBBP
- DB/OSAM BUFFER POOL
- DBLR
- DB/DFSDBLR0 MODULE
- SUBQ
- TM/TM SUBQUEUES
- DBSL
- DB/DB CHECKPOINT
- USER
- DC/USER
- CCTL
- SYS/DBCTL RESOURCE
- VTCB
- SYS/CBTS VTCB POOL
- VLQB
- SYS/CBTS LQB POOL
- CBTS
- SYS/CBTS POOLS (ALL)
- BLKM
- TM/SMB QUEUE HASH TABLE
- QMGR
- SYS/QUEUE MANAGER
- QBSL
- SYS/QUEUE BUFFER
- SMGT
- SYS/STORAGE MANAGEMENT
- DBLK
- SYS/DEPENDENT REGION
- XCNQ
- DB/EXCLUSIVE ENQ/DEQ
- ACTL
- SYS/STATISTICS
- LOGL
- SYS/LOGGER
When a system checkpoint is taken during the time the monitor is active, latch conflict statistics are reset to zero, thus corrupting the values presented in this report. If this situation exists, the following message will be inserted at the top of the report:
**** A CHECKPOINT OCCURRED DURING MONITOR RUN **** **** LATCH CONFLICT STATISTICS ARE INVALID **** **** SEE UTILITIES REFERENCE MANUAL ****However, if the master terminal operator issues the /CHECKPOINT command with the STATISTICS keyword parameter, latch conflict statistics are reset to zero, but the IMS monitor is not notified. Therefore, DFSUTR20 cannot detect that the statistics have been corrupted and does not issue this message.
Recommendation: Do not issue statistics checkpoints while the monitor is running.The different types of latches and the counters that exhibit the level of contention are given in the Latch Conflict Statistics report. The following example shows a sample of the latch-conflict-statistics report. The entries are organized according to the latch names.
IMS MONITOR ** GENERAL REPORTS ** TRACE START 1993 209... LATCH CONFLICT STATISTICS LATCH COUNT AT AT NAMES FIELD START END DIFF. LOGL CONTENTIONS 0 0 0 SMGT CONTENTIONS 0 0 0 XCNQ CONTENTIONS 0 0 0 ACTL CONTENTIONS 0 0 0 CBTS CONTENTIONS 0 0 0 DBLK CONTENTIONS 0 0 0