Using Caché Objects - InterSystems Documentation

Object Synchronization
This functionality prevents creating infinite loops in which two databases continually update
each other with the same set of transactions.
17.2 Running an Update
This process involves preparing for the update and then running the update itself.
17.2.1 Preparing for the Update
Object synchronization requires that the sites have data with matching sets of GUIDs. If you
are starting with an already-existing database that does not yet have GUIDs assigned for its
records, you need to assign a GUID to each instance (record) in the database, and then make
sure there are matching copies of the database on each site. In detail, the process is:
1. For each class being synchronized, set the value of the OBJJOURNAL parameter to 1 or
2. This activates the logging of filing operations (that is, insert, update, or delete) within
each transaction; this information is stored in the ^OBJ.JournalT global.
If OBJJOURNAL equals 1, then the property values that are changed in filing operations
are stored in the system journal file; during synchronization, data that needs to be synchronized
is retrieved from that file.
If OBJJOURNAL equals 2, then the property values that are changed in filing operations
are stored in the ^OBJ.Journal global; during synchronization, data that needs to be
synchronized is retrieved from that global. Note that storing information in the global
increases the size of the database very quickly.
2. For each class being synchronized, set the value of its GUIDENABLED parameter to 1;
this tells Caché to allow the class to be stored with GUIDs. You can do this in Studio,
adding the following line to the class definition:
Parameter GUIDENABLED = 1;
Note that if this value is not set, the synchronization does not work properly. Also, you
must set GUIDENABLED for serial classes, but not for embedded objects.
3. For each class being synchronized, give each object instance its own GUID by running
the AssignGUID method:
Set Status = ##Class(%Library.GUID).AssignGUID(classname,displayoutput)
where
150 Using Caché Objects