apache/cassandra · error · IllegalArgumentException

Hint of bytes is too large - the maximum size is

Error message

Hint of %s bytes is too large - the maximum size is %s

What it means

HintsBuffer.allocate() throws IllegalArgumentException when a hint (plus its per-entry overhead) does not fit within half of the allocated slab capacity. The hints buffer slab has a fixed size, and an incoming hint larger than that threshold can never be buffered, so it is rejected at allocation time rather than corrupting the slab.

Solutions

  1. Increase max_hinted_handoff / hints buffer configuration so the slab can hold workload-sized hints, or reduce mutation size.
  2. Split very large batches into smaller mutations; Cassandra recommends batches under ~0.5MB anyway.
  3. If the node receiving hints cannot handle the size, let the client retry writes directly to the replica once it returns instead of relying on hinted handoff.
  4. Tune cassandra.yaml hints settings (max_hint_window, hint buffer sizing) consistently across the cluster.

Example fix

// before
// one huge mutation hinted while replica is down
session.execute(veryLargeBatchInsert);
// after
for (List<Statement> chunk : Lists.partition(statements, 100))
    session.execute(BatchStatement.newInstance(BatchStatement.Type.UNLOGGED, chunk));
Defensive patterns

Strategy: try-catch

Validate before calling

// reject oversized batches before writing when a replica may be down
if (estimatedSerializedSize(mutation) > maxHintSize())
    throw new IllegalArgumentException("mutation too large to hint");

Try / catch

try { hintsService.write(descriptor, hint); } catch (IllegalArgumentException e) { logger.warn("Hint too large for buffer, dropping: {}", e.getMessage()); }

Prevention

When it happens

Trigger: Writing a hint whose serialized mutation is larger than the hints buffer slab allows — typically a huge batch mutation, very large partition update, or a row count/size that inflates the hint beyond slab capacity / 2. Reached via HintsService/allocator when buffering hints for a down node.

Common situations: Very large batchlog-sized batches applied while a replica is down; max_hinted_handoff or buffer sizes configured small while workloads emit giant mutations; migration from clusters with bigger hints buffers; huge counters or wide partitions exceeding the hint ceiling.

Understand the failure class

Background: payload too large / request exceeds maximum size: why libraries cap bytes and how to fix oversize payloads — this error's family across 50 libraries.

Related errors

AI-assisted analysis of apache/cassandra@88fd0f6a0e (2026-09-10). Data as JSON: /api/errors/d7c0b9b1240787ad. Report an issue: GitHub.

Appendix: source

Thrown at src/java/org/apache/cassandra/hints/HintsBuffer.java:154

                Integer offset = bufferOffsets.poll();

                if (offset == null)
                    return endOfData();

                int totalSize = slab.getInt(offset) + ENTRY_OVERHEAD_SIZE;

                return flyweight.clear().position(offset).limit(offset + totalSize);
            }
        };
    }

    Allocation allocate(int hintSize)
    {
        int totalSize = hintSize + ENTRY_OVERHEAD_SIZE;

        if (totalSize > slab.capacity() / 2)
        {
            throw new IllegalArgumentException(String.format("Hint of %s bytes is too large - the maximum size is %s",
                                                             hintSize,
                                                             slab.capacity() / 2));
        }

        OpOrder.Group opGroup = appendOrder.start(); // will eventually be closed by the receiver of the allocation
        try
        {
            return allocate(totalSize, opGroup);
        }
        catch (Throwable t)
        {
            opGroup.close();
            throw t;
        }
    }

    private Allocation allocate(int totalSize, OpOrder.Group opGroup)
    {

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