What causes "index[%d] >= size[%d] or < 0" in apache/druid?

Iterate using size() as the exclusive upper bound

apache/druid · error · IAE

index[%d] >= size[%d] or < 0

Error message

index[%d] >= size[%d] or < 0

What it means

ArrayBasedIndexedInts.get(int) bounds-checks the index against the current active size, throwing IAE when the index is negative or >= size. The expansion array may be larger than the active size, so checking against size (not array length) preserves semantics.

Source

Thrown at processing/src/main/java/org/apache/druid/segment/data/ArrayBasedIndexedInts.java:91

    this.size = size;
  }

  public void setValue(int index, int value)
  {
    expansion[index] = value;
  }

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

  @Override
  public int get(int index)
  {
    if (index < 0 || index >= size) {
      throw new IAE("index[%d] >= size[%d] or < 0", index, size);
    }
    return expansion[index];
  }

  @Override
  public void inspectRuntimeShape(RuntimeShapeInspector inspector)
  {
    // nothing to inspect
  }
}

View on GitHub (pinned to 9b90983fd2)

Solutions

Iterate using size() as the exclusive upper bound
Re-read size() after any resize/setValues call
Ensure index >= 0 before calling get

Example fix

// before
for (int i = 0; i < arr.length; i++) { int v = indexed.get(i); }
// after
for (int i = 0; i < indexed.size(); i++) { int v = indexed.get(i); }

Defensive patterns

Strategy: validation

Validate before calling

if (index >= 0 && index < indexed.size()) { int v = indexed.get(index); }

Type guard

boolean inRange(IndexedInts v, int i) { return i >= 0 && i < v.size(); }

Try / catch

try { return indexed.get(index); } catch (IAE e) { return Indexable.NOT_FOUND; }

Prevention

Always bound loops by size(), never by array length
Re-fetch size() after any mutation
Use indexed iteration (iterator()) instead of manual index math where possible

When it happens

Trigger: Calling get(index) with index < 0 or index >= size on an IndexedInts, typically from row-iteration code using a stale size or wrong loop bound.

Common situations: Iterating with the backing array length instead of size(); reusing a resized ArrayBasedIndexedInts with old indexes; concurrent modification during iteration.

Related errors

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/87e834c86ff984ac. Report an issue: GitHub.