apache/druid · error · IllegalArgumentException

Index[ ] >= size[ ]

Error message

Index[%d] >= size[%d]

What it means

Indexed.checkIndex validates that an index used to look up an element in an Indexed collection is within [0, size). The library throws this IAE whenever index >= size to fail fast rather than reading out of bounds from the underlying data structure. The odd format is a quirk: '%s' would be more accurate than the mismatched '%d' on the first argument, but the values are index and size.

Solutions

1. Print the collection's size() next to the offending index and fix the loop bound to `index < size()`
2. Ensure the size you bound iteration by comes from the same Indexed instance you call get() on
3. Check for off-by-one errors (i <= size() instead of i < size())
4. If indexes come from another column (e.g. IndexedInts offsets), validate them against this collection's size before lookup

Example fix

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

if (index < 0 || index >= indexed.size()) { throw new IllegalArgumentException("index " + index + " out of range, size=" + indexed.size()); }

boolean inBounds(Indexed<?> col, int i) { return col != null && i >= 0 && i < col.size(); }

try { value = indexed.get(i); } catch (IllegalArgumentException e) { log.error("index %d out of bounds (size=%d)", i, indexed.size()); throw e; }

When it happens

Trigger: Calling Indexed.get(index) (or via IndexedInts/IndexedLongs accessor paths) with an index equal to or greater than the collection's size(), or a stale index held after the column shrank or was re-read.

Common situations: Row-by-row iteration using a cached row count from a different segment version; off-by-one loops (i <= size()); reading a column after the segment was replaced or partially loaded.

Related errors

• != 0
• Index[ ] >= size[ ] or < 0
• index[ ] >= size[ ] or < 0
• Actual Row count mismatch. Expected
• Attempt to add row to swapped-out sink for segment

AI-assisted analysis of apache/druid@9b90983fd2 (2026-09-07). Data as JSON: /api/errors/c0c4742e2a421723. Report an issue: GitHub.

Appendix: source

Thrown at processing/src/main/java/org/apache/druid/segment/data/Indexed.java:127

    return false;
  }

  /**
   * Checks  if {@code index} is between 0 and {@code size}. Similar to Preconditions.checkElementIndex() except this
   * method throws {@link IAE} with custom error message.
   * <p>
   * Used here to get existing behavior(same error message and exception) of V1 {@link GenericIndexed}.
   *
   * @param index identifying an element of an {@link Indexed}
   * @param size size of the {@link Indexed}
   */
  static void checkIndex(int index, int size)
  {
    if (index < 0) {
      throw new IAE("Index[%s] < 0", index);
    }
    if (index >= size) {
      throw new IAE("Index[%d] >= size[%d]", index, size);
    }
  }
}

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