Advanced Topics › Performance Considerations › Control File Internals › Global Management Record (GMR)

Global Management Record (GMR)

The internal structure of the control file is the same regardless of the type of control file medium (DASD, coupling facility, CTC, or XCF) being used. The internal structure of a CA MIM control file always consists of a GMR followed by transactions. The GMR is created as part of the control file formatting process and contains information regarding the following:

• Identity of each system in the MIMplex (system name, alias, index number)
• Current status of the CA MIM address space on each system: active, freed, migrating, and so on
• Time of last control file access for every CA MIM address space
• Control file structural information (BLKSIZE, COMPATLEVEL, and so on)
• Control file statistics (access rates, transaction counts)

The following illustration depicts the internal structure of a CA MIM control file.

The first block of a control file contains the GMR and a number of CA MIM transactions. All subsequent blocks in the CA MIM control file are used to temporarily store CA MIM transactions. Transactions are deleted from the control file as soon as all CA MIM address spaces have read and processed them.