Creating and formatting Log and History File data sets
The Log and the History File are key components of DELTA PLUS and DELTA PLUS VIRTUAL TERMINAL. Both the Log and the History File are pairs of formatted BSAM data sets that record all product updates to a control region. Dual data sets are maintained for both the Log and the History File for recovery and reliability reasons, since both are integral to product operation. Both the dual Log data sets and the dual History File data sets must be available before any updates can be made to the control region. Only one Log data set and one History File data set is necessary for the Log and History File utilities to function.
The IMS control region must have UPDATE authority for the Log and History File data sets.
Note
During IMS control region initialization, the IMS DB/DC SYSGEN linkedit dates are written to the Log and History File control record (if required). The Log and History File SYSGEN dates are also updated following an online change MODBLKS GEN implementation.
To create and format the Log data set
Warning
Log format processing deletes all Log entries. After this is done, an IMS warm start (/NRE without CHKPT 0) or emergency restart (/ERE) is not possible. Therefore, you must cold start IMS after formatting the Log data sets, which will cause all restart information in the Log data sets to be lost.
To create and format the History File data set
Warning
If you reformat an existing History File data set, you destroy the data set contents. You will lose all audit information concerning any changes that have been made to the control regions that are associated with the History File.
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