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SQL Anywhere 11.0.0 » SQL Remote » Replication Design for SQL Remote » SQL Remote installation design » Managing conflicts

 

Designing triggers to avoid errors

Actions performed by triggers are not replicated: triggers that exist at one database in a SQL Remote setup are assumed by the replication procedure to exist at other databases in the setup. When an action that fires a trigger at the consolidated database is replicated at the replicate site, the trigger is automatically fired. By default, the database extraction utility extracts the trigger definitions, so that they are in place at the remote database also.

If a publication includes only a subset of a database, a trigger at the consolidated database may refer to tables or rows that are present at the consolidated database, but not at the remote databases. You can design your triggers to avoid such errors by making actions of the trigger conditional using an IF statement. The following list suggests some ways in which triggers can be designed to work on consolidated and remote databases.

  • Have actions of the trigger be conditional on the value of CURRENT PUBLISHER. In this case, the trigger would not execute certain actions at the remote database.
  • Have actions of the trigger be conditional on the object_id function not returning NULL. The object_id function takes a table or other object as argument, and returns the ID number of that object or NULL if the object does not exist.
  • Have actions of the trigger be conditional on a SELECT statement which determines if rows exist.

The RESOLVE UPDATE trigger is a special trigger type for the resolution of UPDATE conflicts, and is discussed in the section Conflict resolution examples.

The actions of RESOLVE UPDATE triggers are replicated to remote databases, including the database that caused the conflict.