apache/druid · error · IllegalStateException

written out already

Error message

written out already

What it means

IntermediateColumnarLongsSerializer buffers longs into a temp output; once the column has been serialized (written out), the delegate is set and add() is permanently disabled. Calling add() after that transition throws this IllegalStateException because new values can no longer be inserted into the finished column.

Solutions

1. Create a new IntermediateColumnarLongsSerializer for each column instead of reusing a finished one
2. Ensure all add() calls happen before close()/serialization completes
3. Audit aggregation code paths for values arriving after the column was flushed

Example fix

// before
serializer.close();
serializer.add(42L); // throws
// after
serializer.close();
IntermediateColumnarLongsSerializer next = serializerFactory.makeSerializer(...);
next.add(42L);

if (serializer.isDone()) { serializer = factory.makeSerializer(...); }

try { serializer.add(v); } catch (IllegalStateException e) { throw new IOException("column already finalized; create a new serializer", e); }

When it happens

Trigger: Calling add(long) after close()/writeTo() has completed serialization of the column; reusing a serializer across columns without constructing a new instance.

Common situations: Custom segment generation code that keeps appending after finishing a column; aggregation logic that writes more rows than declared to the ingester; reusing a serializer object for multiple input files.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

Related errors

• Incompatible serializer for type
• written out already
• Actual Row count mismatch. Expected
• Attempt to add row to swapped-out sink for segment
• Column capacity exceeded

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/b2bd76ebaf987630. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/segment/data/IntermediateColumnarLongsSerializer.java:97

  @Override
  public void open()
  {
    tempOut = new LongArrayList();
  }

  @Override
  public int size()
  {
    return numInserted;
  }

  @Override
  public void add(long value)
  {
    //noinspection VariableNotUsedInsideIf
    if (delegate != null) {
      throw new IllegalStateException("written out already");
    }
    tempOut.add(value);
    ++numInserted;
    if (numInserted < 0) {
      throw new ColumnCapacityExceededException(columnName);
    }
    if (uniqueValues.size() <= CompressionFactory.MAX_TABLE_SIZE && !uniqueValues.containsKey(value)) {
      uniqueValues.put(value, uniqueValues.size());
      valuesAddedInOrder.add(value);
    }
    if (value > maxVal) {
      maxVal = value;
    }
    if (value < minVal) {
      minVal = value;
    }
  }

View on GitHub (pinned to 9b90983fd2)