private boolean proceedWithMergePlanning(TableDescriptor tableDescriptor) {
    String value = tableDescriptor.getValue(MERGE_ENABLED_KEY);
    return (value == null ? isMergeEnabled() : Boolean.parseBoolean(value))
      && isMasterSwitchEnabled(MasterSwitchType.MERGE);
  }
Returns size of region in MB and if region is not found than -1
hbase-server/src/main/java/org/apache/hadoop/hbase/master/normalizer/SimpleRegionNormalizer.java