Understanding The Update Overwrite Scenario
If a MapStore is in use and the network to the database is available, one or both of the mini-clusters will write updates to the same database. There is a potential for the mini-clusters to overwrite the same cache entry records if modified in both mini-clusters. This overwrite scenario represents a potential data loss, and thus the database design should consider an insert and aggregate on read or version strategy rather than update records in place.
If the network to the database is not available, then based on the configured or coded consistency level or transaction, entry updates are held in cache or updates are rejected (fully synchronous and consistent). When held in cache, the updates will be considered dirty and will be written to the database when it becomes available. You can view the dirty entry counts per cluster member in the Management Center web console (please see the Map Monitoring section).