The journal file header includes a field that stores the name of the previous generation of the journal file when switched, thereby creating a chain of generations (i.e., each journal file points to its previous generation). The resynchronization and rollback operations use this chain to locate all the required generations of a journal file.
The previous generation of a journal file is listed as part of the output of the following command that displays the header information of a journal file. To display the header information of a journal file <jnl_file>, invoke the following command:
mupip journal /show=header <jnl_file>
Invoke the following command to change the previous generation journal file name in the journal file header:
mupip set /jnlfile <jnl_file> /[no]prevjnlfile=<jnlfilename> [-bypass]
Descriptions of the command qualifiers follow:
/JNLFILE
Use this qualifier to indicate that the target for the SET function is a journal file.
<journal file>
Use this qualifier to define the target journal file for the SET function.
/PREVJNLFILE = <jnlfilename>
Use this qualifier to change the name of the previous generation of the journal file in the header of <jnl_file> to <jnlfilename> (e.g., when moving the previous generation journal file to a different location). The file name can be a full path-name or a relative path name; however, before the file-name is stored in the header, it is expanded to its full path-name.
/NOPREVJNLFILE
Use this qualifier to cut the generation link of the journal file <jnl_file>. The name of the previous generation journal file is nullified in the header of <jnl_file>. Such an operation is appropriate when it is assured that there will never be a reason for a rollback to the previous generation journal file.
/BYPASS
Use this qualifier to override the requirement that database files (or their corresponding journal files) affected by the set command be available standalone.
![[Caution]](images/caution.png)
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Caution |
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Changing the previous generation file link when a rollback operation is in progress or when the Source Server is actively replicating, can damage the journal file and hamper recoverability. |
To eliminate the generation link of a journal file, specify noprevjnlfile option as part of the /JOURNAL=<journal-options> qualifier for MUPIP SET. When switching the journal file for database file mumps.dat, use the following command to cut the journal file generation link of the newly created journal file newmumps.mjl:
mupip set
/journal=(before,noprevjnlfile,file=newmumps.mjl)
/file mumps.dat
When journal files are switched as part of the online backup command, the generation link of a journal file can be cut. mupip backup accepts the /JOURNAL=<journal-options> qualifier along with /NEWJNLFILEs qualifier of online backup. Specify the noprevjnlfile as a journal-option to cut the journal file generation link of the newly created journal file.