apache/iceberg · error · UncheckedIOException

Failed to encode partition

Error message

Failed to encode partition

What it means

StructLikeSerializer.encodePartition serializes a partition StructLike into bytes for use as an index key; any IOException from the DataOutputStream is wrapped in an UncheckedIOException with this message. Like serializeKey, the stream is in-memory so failures are unexpected.

Source

Thrown at flink/v2.2/flink/src/main/java/org/apache/iceberg/flink/maintenance/operator/StructLikeSerializer.java:88

    return new SerializedEqualityValues(baos.toByteArray());
  }

  public byte[] encodePartition(StructLike partition, Types.StructType partitionType) {
    List<Types.NestedField> fields = partitionType.fields();
    if (fields.isEmpty()) {
      return EMPTY_PARTITION;
    }

    baos.reset();
    try {
      for (int i = 0; i < fields.size(); i++) {
        writeField(partition, i, fields.get(i).type());
      }

      dos.flush();
    } catch (IOException e) {
      throw new UncheckedIOException("Failed to encode partition", e);
    }

    return baos.toByteArray();
  }

  public static StructLike decodePartition(byte[] encoded, Types.StructType partitionType) {
    PartitionData partition = new PartitionData(partitionType);
    List<Types.NestedField> fields = partitionType.fields();
    if (fields.isEmpty()) {
      return partition;
    }

    try (DataInputStream dis = new DataInputStream(new ByteArrayInputStream(encoded))) {
      for (int i = 0; i < fields.size(); i++) {
        boolean isNull = dis.readBoolean();
        if (isNull) {
          partition.set(i, null);
        } else {

View on GitHub (pinned to 86d9c8fc54)

Solutions

1. Retry the failing Flink task/job; the failure is typically transient.
2. Check the wrapped cause for JVM-level issues (OOM, thread interruption during flush).
3. If reproducible for a specific partition type, file a bug with the partition schema.

try {
  bytes = serializer.encodePartition(partition, partitionType);
} catch (UncheckedIOException e) {
  LOG.error("Partition encoding failed", e.getCause());
  throw e;
}

When it happens

Trigger: IOException raised while writing partition fields in encodePartition during table-change processing in the maintenance operators.

Common situations: Rare runtime/IO fault; often appears alongside broader task failures during checkpoint-heavy maintenance jobs.

Understand the failure class

Background: "JSON serialization failed", "not JSON serializable", "Failed to serialize": why JSON marshaling errors happen and how to fix them — this error's family across 46 libraries.

Related errors

• Failed to serialize sort key
• Failed to serialize sort key
• Fail to serialize data statistics
• Fail to serialize aggregated statistics
• Failed to serialize PK index key

AI-assisted analysis of apache/iceberg@86d9c8fc54 (2026-09-12). Data as JSON: /api/errors/976f39ddadc3ef3d. Report an issue: GitHub.