default void postMergeRegionsCommitAction(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final RegionInfo[] regionsToMerge, final RegionInfo mergedRegion) throws IOException {
  }
This will be called after META step as part of regions merge transaction.
@param ctx the environment to interact with the framework and master
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java