This Service Bulletin contains information about a z/TPF and TPF 4.1 problem that results in a catastrophic 0006DF system error dump. Special consideration for TPF 4.1 customers is included at the end of this bulletin. There will be no TPF 4.1 APAR available.
The system can run out of I/O control blocks (IOBs), which results in a catastrophic 0006DF system error dump, because the system might not be protected if an individual ECB creates an excessive commit scope. To prevent this problem, immediately set your MCMTB value in keypoint A (CTKA) by entering ZCTKA ALTER MCMTB-x , where x is a value from 1024 to 25% of the lowest number of IOBs allocated for any enabled memory configuration in the system. APAR PJ39130 enforces this requirement so that z/TPF systems will no longer allow unlimited commit buffers in the commit scope for an individual ECB.
CTKA field CK1MCB contains the maximum number of commit buffers that can be used in a commit scope. You can change this value by entering the ZCTKA ALTER command with the MCMTB parameter specified. Currently, CK1MCB defaults to zero. A value of zero indicates that unlimited commit buffers can be used, which can cause the system to run out of IOBs and result in a catastrophic 0006DF system error.
With APAR PJ39130, the maximum number of commit buffers (MCMTB) in a commit scope cannot be set to unlimited (zero). The value of MCMTB must be from 1024 to 25% of the number of allocated IOBs.
This APAR includes three (3) changes:
- Updates to CCCTIN copy module ct41.cpy. This change determines if the MCMTB value is valid. If the MCMTB value is not valid, the in core value that is stored in ICRCT macro field ICT_RM_DMAX will be changed to a valid value. If the CTKA field CK1MCB is zero or is higher than 25% of the number of allocated IOBs, the MCMTB value in ICT_RM_DMAX will be set to be 25% of the number of allocated IOBs. If the value in CK1MCB is less than 1024 but not zero, the MCMTB value in ICT_RM_DMAX will be set to 1024.
- Changes were made to the ZCTKA ALTER command. When you enter the ZCTKA ALTER command with the MCMTB parameter specified, the new value is validated. If the number is less than 1024, the command is rejected. If the number is greater than 25% of lowest number of IOBs allocated for any memory configuration, the request is also rejected. In addition, when you enter the ZCTKA ALTER command with the MEMORY and IOB parameters specified, the IOB value is validated. If the new IOB value will result in the MCMTB value being larger than 25% of the number of allocated IOBs, the command is rejected.
- A new parameter was added to the SIP macro CORREQ. The MCMTB parameter was added to provide the ability to set MCMTB in SIP.
You can use information in data collection reports to determine how to set the value for the MCMTB parameter. The system summary report includes the largest size commit scope that existed in the z/TPF system since the last IPL (COMMIT SCOPE BUFFERS PER COMMIT SCOPE-MAX SINCE IPL in the COMMIT/ROLLBACK DATA section of the report). Set the MCMTB value to a value that is larger than this maximum since the last IPL value.
For TPF4.1 systems, change the maximum number of commit buffers by entering the ZCTKA ALTER command with the MCMTB parameter specified with a value from 1024 to 25% of the allocated IOBs.
For questions or concerns about the information in this service bulletin, send an e-mail to TPFQA@US.IBM.COM.