Introduction › How EDIF Prevents Simultaneous Updates When Serialization Is Omitted

How EDIF Prevents Simultaneous Updates When Serialization Is Omitted

EDIF prevents simultaneous updates that occur when a job does not serialize access to a data set or uses the wrong technique to serialize access. Most programs rely on JCL to serialize access to data sets on their behalf. When you specify DISP=OLD on a DD statement in your JCL, z/OS issues an ENQ request that obtains exclusive access to the data set for your job. However, when you specify DISP=SHR, your job obtains shared access, which lets other tasks that request shared access use that data set at the same time.

To prevent other tasks from using the data set, the program that your JCL calls must request serialization. If serialization is not requested, then a simultaneous update can occur. To detect and prevent simultaneous updates, EDIF automatically issues an ENQ request whenever a job issues an OPEN request to update a data set. If you want to detect updates for testing purposes, then you can record updates in an SMF record and run an EDIF activity report against those records. You also can prevent simultaneous updates if you tell EDIF to make subsequent tasks wait for access when a data set is being used.