A fix is available
APAR status
Closed as program error.
Error description
ABEND878-08 occurs due to high use of ECSA storage by an MQ MSTR job in Subpool 231 key 7 SP231 KEY7 K7 Many storage segments shown in IPCS OWNCOMM output have a length of x'000002A0'. The getmains are from CSQSGMN. The storage has eycatchers that look like ........SYSOPR ........245.DB2MST00............ ........CSQ1 ........ where CSQ1 is the queue manager name. The first word of storage is 007102A0, which is associated with an MQ CCB control block. The growth in ECSA occurs when there are repetitive abends when CSQ5CONN calls DB2. During queue manager startup, CSQ5CONN is called on the DB2MST00 internal task in the queue manager to establish the initial connection from the queue manager to DB2. While MQ is attempting to read the queue manager object from DB2, the abend occurs. CSQ5CONN retries and ends gracefully. This causes the DB2MST00 task to end and another to be automatically started. The new task similarly attempts to read the queue manager object, abends, and ends on retry, causing a new task to be started. If the underlying problem is persistent, it causes a loop in the connection processing from MQ to DB2. Because this is during queue manager startup, the CCB control blocks for the tasks are not obtained/freed from the usual PHB pool and are instead obtained using CSQSGETM. The expectation is that these tasks are long running internal tasks, and so the CCBs are not explicitly freed - instead they will be implicitly freed at queue manager shutdown. In normal operation this is fine. However in this situation it leads to the CCB for each failed attempt remaining allocated for the lifetime of the queue manager. The huge number of failed attempts to access DB2 has led to a large amount of ECSA being used by the queue manager. These CCBs should be freed in a more timely manner rather than waiting for queue manager shutdown. For one of the reports of this problem, the underlying problem was repetitive ABENDs seen in LOGDATA associated with SUBFUNCTION DB2 CSQ5CONNREADQMGR and an UNKNOWN module. The PSW was in a vendor module. There could be other underlying abends interrupting the processing. Additional Symptom(s) Search Keyword(s): ABENDS878 878 S878 S0878 000002A0 2A0 x2A0 IEA705I ERROR DURING GETMAIN SYS CODE = 878-08 MSTJCL00
Local fix
Restart the queue manager if possible. Resolve the underlying abend that is preventing the connection from MQ to DB2 from working.
Problem summary
**************************************************************** * USERS AFFECTED: All users of IBM MQ for z/OS Version 9 * * Release 1 Modification 0. * **************************************************************** * PROBLEM DESCRIPTION: Storage leak of SP231 Key 7 ECSA * * storage occurs if tasks repeatedly fail * * during queue manager startup. * **************************************************************** During queue manager startup CSQ3AUGI is called to obtain and free CCB control blocks for tasks started before CSQ3AUCM is available. However CSQ3AUGI only expects to be called to free CCBs during queue manager shutdown, and does not explicitly free the storage used. This can result in CCBs remaining allocated but unused in ECSA until the queue manager shuts down. In the reported case, an external error caused the DB2 connection task to abend and retry repeatedly, resulting in a large number of such CCBs remaining allocated and causing a shortage of ECSA.
Problem conclusion
CSQ3AUGI is changed to explicitly free the CCB when called during queue manager startup.
Temporary fix
Comments
APAR Information
APAR number
PH05604
Reported component name
IBM MQ Z/OS V9
Reported component ID
5655MQ900
Reported release
100
Status
CLOSED PER
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2018-11-21
Closed date
2019-01-11
Last modified date
2019-02-02
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UI60628
Modules/Macros
CSQ3AUGI
Fix information
Fixed component name
IBM MQ Z/OS V9
Fixed component ID
5655MQ900
Applicable component levels
R100 PSY UI60628
UP19/01/26 P F901 ¢
Fix is available
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Document Information
Modified date:
02 February 2019