default void preTableFlush(final ObserverContext<MasterCoprocessorEnvironment> ctx,
    final TableName tableName) throws IOException {
  }
Called before the table memstore is flushed to disk.
@param ctx       the environment to interact with the framework and master
@param tableName the name of the table
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/MasterObserver.java