NoSQL Basics and Skills
NoSQL Basics and Skills

A tricky file handling point in CICS. During Read how CICS handles integrity. There are two ways -One way is read waits till update completes, and option -2 is first READ completes and then UPDATE completes.

Details of CICS READ:

The record is read with a level of read integrity provided by a VSAM shared lock that lasts for the duration of the request.

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If the record is being modified by another task, which therefore holds an exclusive lock, the READ request waits until the update is complete (unless NOSUSPEND is also specified) as follows:

  • For a READ request against a non-recoverable file, the READ completes as soon as any VSAM request performing the update completes.
  • For a READ request against a recoverable file, the READ request completes when the updating task completes its next sync point or rollback.

CICS READ Syntax from IBM manual:

READ--FILE(filename)--+------------------------------+------->
                         +-UNCOMMITTED------------------+   
                         +-CONSISTENT-------------------+   
                         +-REPEATABLE-------------------+   
                         '-UPDATE--+------------------+-'   
                                   '-TOKEN(data-area)-'     

>--+-INTO(data-area)-+--RIDFLD(data-area)----------------------->
   '-SET(ptr-ref)----'                      

>--+------------------------------------+----------------------->
   '-KEYLENGTH(data-value)--+---------+-'   
                            '-GENERIC-'     

>--+--------------------------------------+--+--------+--------->
   +-SYSID(systemname)--LENGTH(data-area)-+  +-DEBKEY-+   
   '-LENGTH(data-area)--------------------'  +-DEBREC-+   
                                             +-RBA----+   
                                             +-RRN----+   
                                             '-XRBA---'   

   .-EQUAL-.                  
>--+-------+--+-----------+------------------------------------><
   '-GTEQ--'  '-NOSUSPEND-'
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