apache/druid · error · java.lang.UnsupportedOperationException

StringFirstAggregator does not support getLong()

Error message

StringFirstAggregator does not support getLong()

What it means

StringLastBufferAggregator cannot produce a long from its stored timestamp/string pair, so getLong(ByteBuffer,int) throws UnsupportedOperationException. This enforces that string aggregators are consumed through their string result path.

Source

Thrown at processing/src/main/java/org/apache/druid/query/aggregation/firstlast/last/StringLastBufferAggregator.java:121

    }
  }

  @Override
  public Object get(ByteBuffer buf, int position)
  {
    return StringFirstLastUtils.readPair(buf, position);
  }

  @Override
  public float getFloat(ByteBuffer buf, int position)
  {
    throw new UnsupportedOperationException("StringFirstAggregator does not support getFloat()");
  }

  @Override
  public long getLong(ByteBuffer buf, int position)
  {
    throw new UnsupportedOperationException("StringFirstAggregator does not support getLong()");
  }

  @Override
  public double getDouble(ByteBuffer buf, int position)
  {
    throw new UnsupportedOperationException("StringFirstAggregator does not support getDouble()");
  }

  @Override
  public void close()
  {
    // no resources to cleanup
  }

  @Override
  public void inspectRuntimeShape(RuntimeShapeInspector inspector)
  {
    inspector.visit("timeSelector", timeSelector);

View on GitHub (pinned to 9b90983fd2)

Solutions

Extract the value via get(ByteBuffer,int) (the string pair) instead of getLong
Choose a numeric aggregator (longFirst/longLast) when a long is needed
Check AggregatorFactory.getTypeName() and only call the matching typed accessor
Apply SQL CAST(... AS BIGINT) if the string should be interpreted as a long

Example fix

// before
long l = bufAgg.getLong(buf, position); // throws
// after
Object val = bufAgg.get(buf, position); // string result
long l2 = Long.parseLong((String) val); // only if conversion intended

Defensive patterns

Strategy: type-guard

Validate before calling

if ("long".equals(factory.getTypeName())) { l = bufAgg.getLong(buf, pos); } else { /* string path */ }

Type guard

static boolean hasLongAccessor(AggregatorFactory f) { return f.getTypeName().equals("long"); }

Try / catch

try { l = bufAgg.getLong(buf, pos); } catch (UnsupportedOperationException e) { l = 0L; }

Prevention

Check the metric type before integer result extraction
Use longFirst/longLast for integer aggregations
Convert string results explicitly (parseLong) when numeric output is intended

When it happens

Trigger: Calling getLong(buf, position) on a StringLastBufferAggregator instance during result collection when the metric is assumed numeric.

Common situations: Generic result merge/extraction code in custom extensions; tests that call all three numeric accessors on every buffer aggregator; SQL plans that expect a numeric type but were given stringFirst/stringLast.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/336143f56240be4d. Report an issue: GitHub.