apache/hadoop · error · UnsupportedOperationException

${className} does not support setting the readahead caching

Error message

${className} does not support setting the readahead caching strategy.

What it means

Error "${className} does not support setting the readahead caching strategy." thrown in apache/hadoop.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSDataInputStream.java:181

  @Override
  public FileDescriptor getFileDescriptor() throws IOException {
    if (in instanceof HasFileDescriptor) {
      return ((HasFileDescriptor) in).getFileDescriptor();
    } else if (in instanceof FileInputStream) {
      return ((FileInputStream) in).getFD();
    } else {
      return null;
    }
  }

  @Override
  public void setReadahead(Long readahead)
      throws IOException, UnsupportedOperationException {
    try {
      ((CanSetReadahead)in).setReadahead(readahead);
    } catch (ClassCastException e) {
      throw new UnsupportedOperationException(in.getClass().getCanonicalName() +
          " does not support setting the readahead caching strategy.");
    }
  }

  @Override
  public void setDropBehind(Boolean dropBehind)
      throws IOException, UnsupportedOperationException {
    try {
      ((CanSetDropBehind)in).setDropBehind(dropBehind);
    } catch (ClassCastException e) {
      throw new UnsupportedOperationException("this stream does not " +
          "support setting the drop-behind caching setting.");
    }
  }

  @Override
  public ByteBuffer read(ByteBufferPool bufferPool, int maxLength,
      EnumSet<ReadOption> opts) 

View on GitHub (pinned to 2add963021)

Solutions

1. Only call setReadaheadStrategy on streams whose wrapped input supports it (e.g. HDFS streams).
2. Guard the call with an instanceof/capability check and skip when unsupported.

When it happens

Trigger: Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSDataInputStream.java:181 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/c2b980500dc49900. Report an issue: GitHub.