apache/iceberg · error · UncheckedIOException

Failed to close equality delta writer

Error message

Failed to close equality delta writer

What it means

PartitionedDeltaWriter.close runs RowDataDeltaWriter::close for every per-partition delta writer via Tasks; if any of those closes throws IOException it is wrapped as UncheckedIOException with this message. Closing writes the remaining data/delete files, so this failure can leave files partially written.

Source

Thrown at flink/v2.3/flink/src/main/java/org/apache/iceberg/flink/sink/PartitionedDeltaWriter.java:97

      writer = new RowDataDeltaWriter(copiedKey, dvFileWriter());
      writers.put(copiedKey, writer);
    }

    return writer;
  }

  @Override
  public void close() {
    try {
      super.close();
      Tasks.foreach(writers.values())
          .throwFailureWhenFinished()
          .noRetry()
          .run(RowDataDeltaWriter::close, IOException.class);

      writers.clear();
    } catch (IOException e) {
      throw new UncheckedIOException("Failed to close equality delta writer", e);
    }
  }
}

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Inspect the wrapped IOException cause to find the failing filesystem and fix storage/credentials/network issues
2. Increase executor ulimit (nofile) or reduce partition cardinality to limit concurrently open writers
3. Retry the job from the last checkpoint; Iceberg commits are transactional so partial files are cleaned up
4. Enable retry/backoff settings for the object store filesystem to absorb transient throttling

try {
  partitionedWriter.close();
} catch (UncheckedIOException e) {
  LOG.error("delta writer close failed; failing task so checkpoint retries", e.getCause());
  throw new IOException(e.getCause()); // rethrow as checkpoint-recoverable failure
}

When it happens

Trigger: Closing a PartitionedDeltaWriter (e.g. at checkpoint or record end) when the underlying writers' close() hits IOException — disk full, filesystem outage, object-store throttling during file upload.

Common situations: S3 503/slow-down under load; HDFS DataNode failures; disk quota exceeded on executors; too many open files (ulimit) with high partition cardinality.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• Failed to close equality delta writer
• Failed to close equality delta writer
• Failed to close equality delta writer
• Already closed files for partition:
• Failed to close current writer

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/e36e734c8946d037. Report an issue: GitHub.