Changes to the value of a USERVAR are not propagated by VTAM® at the time of the change. Instead, when a domain using a USERVAR to establish a session encounters a specific USERVAR for the first time, it uses an adjacent SSCP table to perform a cross-domain search to obtain the USERVAR value. Subsequent attempts to use the same USERVAR can result in a repeat of the cross-domain search to update the USERVAR value, depending on the value of the TYPE operand. The TYPE operand is specified on the MODIFY USERVAR command when the USERVAR is created. The TYPE operand is copied, along with the USERVAR value, when an automatic USERVAR is created in another domain. Following are the types of USERVARs:

Static USERVAR

The value is assumed not to change. It is saved as an automatic USERVAR upon initial use but is not updated automatically using the cross-domain search process (unless the existing copy of the automatic USERVAR is explicitly deleted by the operator).

Dynamic USERVAR

The value is expected to remain relatively stable but change occasionally (for example, when an XRF takeover occurs). To establish a cross-domain session to an application program identified by a dynamic USERVAR, VTAM must recheck the USERVAR value after every abnormal session termination involving the application program that it references.

DYNAMIC is the default value for the MODIFY USERVAR command and is recommended for use within XRF complexes.

Volatile USERVAR

The value is expected to change often. Rather than creating an automatic copy of the USERVAR, a remote VTAM repeats the cross-domain search to reestablish the USERVAR current value each time it is referenced to establish a session. Because of the additional search flow that is necessary for each session establishment, use of volatile USERVARs might have a substantial impact on the time required for session establishments.