@Override
        public String toString() {
            return "MigrationState{" +
                    "totalMaps=" + totalMaps +
                    ", mapsMigrated=" + mapsMigrated +
                    ", entriesMigrated=" + entriesMigrated +
                    '}';
        }
Migrate the data for refStreamId into destinationStore
stroom-pipeline/src/main/java/stroom/pipeline/refdata/store/offheapstore/StoreMigrator.java