private void preMergeRegionsCommit(final MasterProcedureEnv env) throws IOException {
    final MasterCoprocessorHost cpHost = env.getMasterCoprocessorHost();
    if (cpHost != null) {
      @MetaMutationAnnotation
      final List<Mutation> metaEntries = new ArrayList<>();
      cpHost.preMergeRegionsCommit(regionsToMerge, metaEntries, getUser());
      try {
        for (Mutation p : metaEntries) {
          RegionInfo.parseRegionName(p.getRow());
        }
      } catch (IOException e) {
        LOG.error("Row key of mutation from coprocessor is not parsable as region name. "
          + "Mutations from coprocessor should only be for hbase:meta table.", e);
        throw e;
      }
    }
  }
Post merge region action
@param env MasterProcedureEnv
hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/MergeTableRegionsProcedure.java