Deadlock Between Multiple DADS Plus batch interface DADB Transactions. One DADB holding ENQUEUE on itself and causes DADS batch interface jobs and CICS to hang.

Products

• DADS Plus

Issue/Introduction

Region locked up with multiple DADB transactions running.  We recycled the CICS region to resolve the situation.  Two of the DADB transactions was shown as running in SYSVIEW.  The 3rd DADB transaction shows as ENQUEUE  KCADDR.  None of the transactions could be purged.  No one could sign on to the CICS region and was not recognizing any input from the console.  We have captured an SVC dump and can provide several excerpts from the SYSVIEW monitor to show the condition at the region. 

Environment

Z/OS 

CICS

Cause

The console dump shows that program DADSLOCT +x'253C', running on behalf of DADB task# 41368, had issued a DYNALLOC SVC directly on the QR TCB. GRS then put the QR TCB into a wait, needing an ENQ owned by the FO TCB.
 At dump time, the QR TCB time-of-day clock had not been updated for over 2 hours.
DADB task# 41371 was trying to open file SMPSF (dataset PINVPCS.SSC.SMPS.KE). The OPEN request was issued under the FO TCB, but VSAM module IDA019SE +3FE (UA92647) put the FO TCB into a wait, apparently due to reaching EOV.
DADS Plus  should not be issuing the DYNALLOC SVC directly on the QR TCB as it can cause the entire CICS region to hang, as it did here.

Resolution

With regard to DADS issuing the SVC99 from the QR TCB, Please check that you have SUBTASKING set as follows to prevent the SVC99 from being issued on the QR TCB. The SUBTASKING parameter
is stored in the DADS Control file and can be updated by executing the DADBCNTL utility program as outlined in the DADS Plus r 4.0 installation guide.

SUBTASKING  ==>     Y         Y

The DADC online transaction will show the value of SUBTASKING parameter and the other parameters stored on the DADS control file.

Here is the description of SUBTASKING from the Installation guide.

SUBTASKING N/Y 

Determines how online SVC99s will be issued.

N 
Specifies that online SVC99s be issued under the CICS TCB with no
mounting of off-line volumes requested.

Y 
Specifies that all online SVC99s be issued by an OS subtask with
mounting of off-line volumes requested. A CICS shutdown will wait
until any outstanding mount requests are satisfied or canceled. Any
unusually long waits in SVC99 will not affect CICS processing. A small
amount of OS core will be required when Advantage CA-DADS Plus
for CICS allocates or deallocates a file or DBD, and a shortage of OS
core may cause the SVC99 to be issued within the CICS TCB, or an SER
error during the attaching of the SVC99 OS subtask may occur. SVC99s
issued during initialized are always issued under the CICS TCB,
regardless of this option.

The client changed subtasking to Y which resolved the problem.