CICS follows data integrity in different ways for different file types. UPDATE guarantees read integrity. The mechanism used to ensure data integrity depends on the type of file resource:
Data Integrity Methods That CICS Follows
- For a VSAM file accessed in RLS mode, the record to be updated is locked by the SMSVSAM server.
- For a VSAM file accessed in non-RLS mode, the record to be updated is locked by CICS and, in addition, the control interval containing the record is held in exclusive control by VSAM.
- For a VSAM file accessed in non-RLS mode, and log(UNDO), CICS holds a record lock until the task syncpoints.
- For a BDAM file, the record to be updated is held in exclusive control by BDAM.
- For a user-maintained data table, the record to be updated is locked by CICS.
- For a CICS-maintained data table, the record to be updated is locked by CICS and, in addition, the control interval containing the record is held in exclusive control by VSAM. The VSAM control interval lock is required because changes to the data table are reflected in the source data set, which is accessed in non-RLS mode.
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