default void preWALRoll(ObserverContext<? extends WALCoprocessorEnvironment> ctx, Path oldPath,
    Path newPath) throws IOException {
  }
Called before rolling the current WAL
@param oldPath the path of the current wal that we are replacing
@param newPath the path of the wal we are going to create
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/WALObserver.java