Using Caché Objects - InterSystems Documentation

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• If two changes require reconciliation. This requires determining if the two changes were
to a common property or to non-intersecting sets of properties.
17.1.3 The SyncSet and SyncTime Objects
When two databases are to be synchronized, each has transactions in it that the other lacks.
This is illustrated in the following diagram:
Two Unsynchronized Databases
Here, database A and database B have been synchronized at transaction 536 for database A
and transaction 112 for database B. The subsequent transactions for each database need to
be updated from each to the other. To do this, Caché uses what is called a SyncSet object.
This object contains a list of transactions that are used to update a database. For example,
when synchronizing database B to database A, the default contents of the SyncSet object are
transactions 547, 555, 562, and 569. Analogously, when synchronizing database B to database
A, the default contents of the SyncSet object are transactions 117, 124, 130, and 136. (The
transactions do not use a continuous set of numbers, because each transaction encapsulates
multiple inserts, updates, and deletes — which themselves use the intermediate numbers.)
Each database holds a record of its synchronization history with the other. This record is
called a SyncTime table. For database, its contents are of the form:
Database Namespace Last Transaction Sent Last Transaction Received
------------------------------------------------------------------------------
B User 536 112
Using Caché Objects 147