Synchronization Failure Compensation

If implicit synchronization fails for a target resource (for example, due to a policy validation failure on the target, or the target being unavailable), the synchronization operation stops at that point. In this scenario, a record might be changed in the repository, and in the targets on which synchronization was successful, but not on the failed target, or on any targets that would have been synchronized after the failure. This can result in disparate data sets across resources. Although a reconciliation operation would eventually bring all targets back in sync, reconciliation can be an expensive operation with large data sets.

You can configure synchronization failure compensation to prevent data sets from becoming out of sync. This mechanism involves reverting an implicit synchronization operation if it is not completely successful across all configured mappings.

Failure compensation ensures that either all resources are synchronized successfully, or that the original change is rolled back. This mechanism uses an onSync script hook in the managed object configuration (conf/managed.json file). The onSync hook references a script (compensate.js) located in the /path/to/openidm/bin/defaults/script directory. This script prevents partial synchronization by "reverting" a partial change in the event that all resources are not synchronized.

The following excerpt of a sample managed.json file shows the addition of the onSync hook:

...
"onDelete" : {
    "type" : "text/javascript",
    "file" : "onDelete-user-cleanup.js"
},
"onSync" : {
    "type" : "text/javascript",
    "file" : "compensate.js"
},
"properties" : [
    ... 

With this configuration, a change to a managed object triggers an implicit synchronization for each configured mapping, in the order in which the mappings are defined. If synchronization is successful for all configured mappings, IDM exits from the script. If synchronization fails for a particular resource, the onSync hook invokes the compensate.js script, which attempts to revert the original change by performing another update to the managed object. This change, in turn, triggers another implicit synchronization operation to all external resources for which mappings are configured.

If the synchronization operation fails again, the compensate.js script is triggered a second time. This time, however, the script recognizes that the change was originally called as a result of a compensation and aborts. IDM logs warning messages related to the sync action (notifyCreate, notifyUpdate, notifyDelete), along with the error that caused the sync failure.

If failure compensation is not configured, any issues with connections to an external resource can result in out of sync data stores.

With the compensate.js script, any such errors will result in each data store retaining the information it had before implicit synchronization started. That information is stored, temporarily, in the oldObject variable.