public void preWALRoll(Path oldPath, Path newPath) throws IOException {
    execOperation(coprocEnvironments.isEmpty() ? null : new WALObserverOperation() {
      @Override
      protected void call(WALObserver observer) throws IOException {
        observer.preWALRoll(this, oldPath, newPath);
      }
    });
  }
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/regionserver/wal/WALCoprocessorHost.java