Latch identification

RRS uses numerous latches to establish an orderly flow during transaction processing. If a unit of work hangs up while holding a latch, other work units may also wait for the latch causing a hung transaction. The Display GRS Contention (D GRS,C) command, will establish there is contention but does not provide sufficient information to quickly narrow the problem down to a particular transaction. If contention persists, the command: D GRS,ANALYZE,LATCH,DEPENDENCY,DETAIL will display more information along with the latch identifiers that have been established for some of the RRS latches. For the RRS address space, the following Latch Identifiers have been created.

Table 1. Latch Identifiers
Latch set	Latch identifier	Identifier description	Identify the transaction by RRS panel option:
CD Context Data	CD URID: `urid`	urid - Unit of Recovery Identifier	3 - Display/Update RRS Unit of Recovery information and search on the urid.
RM Resource Manager	RM: `rmname`	rmname – Resource Manager Name	2 - Display/Update RRS related Resource Manager information and search on the rmname.
SHT System Hash Table	SHT System: `sysname`	sysname – name of the system that owns the SHT. See note below.	If SHT contention persists, contact your IBM® Support Center.
SHT System Bucket Hash Table	SHT Bucket: `number` System: `sysname`	number – bucket number. sysname – name of the system that owns the SHT. See note below.	If SHT Bucket contention persists, contact your IBM Support Center.
SHE Sysplex Hash Element	SHE SURID: `surid`	surid - Sysplex Unit of Recovery Identifier	3 - Display/Update RRS Unit of Recovery information and search on the surid.
UR Units of Recovery	UR URID: `urid`	urid - Unit of Recovery Identifier	3 - Display/Update RRS Unit of Recovery information and search on the urid.
UR Main State Log	MainQ Log: `log`	log – UR Log Stream Name	If State Log contention persists, contact your IBM Support Center.
UR Compression State Log	CompQ Log: `log`	log – UR Log Stream Name	If State Log contention persists, contact your IBM Support Center.

Note: For the SHT and SHT Bucket Latch Sets, “Unknown” might be displayed for the system name. The Unknown SHT table keeps track of transactions that are moving between systems sometimes because of system restart problems.

As an alternative to identify the transaction by the RRS panels, the DISPLAY RRS command (D RRS,RM or D RRS,UR) can be used for CD, RM, and UR latch sets.

The following output is an example from command: D GRS,ANALYZE,LATCH,DEPENDENCY,DETAIL

SY1  ISG374I 16.25.10 GRS ANALYSIS 220
   DEPENDENCY ANALYSIS: ENTIRE SYSTEM
   ----- LONG WAITER #1
            JOBNAME: RRS       (ASID=002A, TCB=004E03E8)
            REQUEST: EXCLUSIVE                       LT:7EA8907800000007
   WAITING  00:59:17 FOR RESOURCE (CREATOR ASID=002A)
   SYS.ATRURCPO.00000001                            LST:7EA8C10000000124
   5: UR URID:C30C9DB97E0AC0000000000201020000
            JOBNAME: MAINASID  (ASID=0030, TCB=004E6D90)
            REQUEST: EXCLUSIVE                       LT:7EA8B010000000A2
   ANALYSIS ENDED: THIS UNIT OF WORK IS NOT WAITING

In the example, the Latch Identifier is: 
UR URID:C30C9DB97E0AC0000000000201020000.

For more information about the DISPLAY RRS and DISPLAY GRS commands, see z/OS MVS System Commands.