Use the IXGUPDAT service to modify the UTC time stamp control information for a log stream. Once modified, the next log block written to the log stream will be assigned a UTC time stamp equal to or greater than the one specified on the IXGUPDAT request.
For coupling facility log streams, the time stamp for a log stream maintained in the coupling facility list controls.
For DASD-only log streams, the time stamp for a log stream maintained in the local control blocks for the system associated with the log stream and the staging data set control records.
On the IXGUPDAT service, you must supply a time stamp that is equal to or greater than the current time stamp maintained in the Log Stream Control information. You can obtain the current time stamp for the log stream by issuing the IXGQUERY service.
You must be in task mode to issue the IXGUPDAT service or else the request is rejected. The program issuing IXGUPDAT must also have specified AUTH=WRITE on the IXGCONN request to connect to the log stream to issue this request.
Why would I need to change a time stamp on a log stream? The IXGUPDAT service is useful mainly to coupling facility log streams. If an application writes to multiple coupling facility log streams at the time of a failure necessitating recovery processing, database recovery processing truncates the log streams to the latest point consistent across all the log streams. This can mean a loss of data. For example, let's say an application writes to two log streams. In log stream 1, the last log block written was at 9 A.M.. In log stream 2, the last log block was written at 9:15 A.M.. The recovery process logically truncates log stream 2 data to 9 A.M., to be consistent with log stream 1 for recovery. This means that the data written to log stream 2 between 9:00 and 9:15 is lost.
In this situation, you would use IXGUPDAT to update the time stamp for log stream 1 to 9:15 or greater so that all data for both log streams can be recovered. All data written to the two log streams up until 9:15 A.M can then be recovered. IXGUPDAT lets you advance the time stamp for a log stream or streams to the latest time among all the log streams. This ensures that log streams have a consistent time stamp and include all the data written to any of the log streams.