apache/hadoop · error · UnsupportedOperationException

this stream does not support setting the drop-behind caching

Error message

this stream does not support setting the drop-behind caching setting.

What it means

Error "this stream does not support setting the drop-behind caching setting." thrown in apache/hadoop.

Source

Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSDataInputStream.java:192

  @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) 
          throws IOException, UnsupportedOperationException {
    try {
      return ((HasEnhancedByteBufferAccess)in).read(bufferPool,
          maxLength, opts);
    }
    catch (ClassCastException e) {
      ByteBuffer buffer = ByteBufferUtil.
          fallbackRead(this, bufferPool, maxLength);
      if (buffer != null) {
        extendedReadBuffers.put(buffer, bufferPool);
      }

View on GitHub (pinned to 2add963021)

Solutions

1. Check stream capabilities before calling setDropBehind.
2. Use a stream implementation that supports drop-behind caching, or omit the setting.

When it happens

Trigger: Thrown at hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FSDataInputStream.java:192 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/1e8140ac7a404d47. Report an issue: GitHub.