wrangler queues consumer failed: batch size too large

wrangler queues consumer failed: batch size too large

TL;DR

The consumer's maxbatchsize exceeds what the handler can process (time or memory), so batches fail. Lower maxbatchsize, make the handler faster, or split work. The batch setting must fit the handler's real capacity.

wrangler queues consumer failed: batch size too large

Steps

1. Check the consumer's maxbatchsize and the handler's actual per-message cost. Expected: The mismatch is quantified.

2. Lower maxbatchsize to what the handler reliably processes within limits. Expected: Batches complete.

3. Speed up the handler if the batch size is business-required: less per-message work, more parallelism. Expected: Capacity rises.

4. Watch for poison messages: one bad message can fail the whole batch repeatedly. Expected: Dead-letter it.

5. Set max_retries and a dead-letter queue so failures are bounded. Expected: The queue stays healthy.

When to use

• queue consumers fail on batch size
• handlers time out mid-batch
• batch settings were raised recently

When not to use

• single messages fail (that is the handler, not the batch)
• the error is on produce, not consume (different path)
• the batch size is already small (look for poison messages)

Tool compatibility

• wrangler
• Cloudflare Queues

Variant phrasings

• "queues consumer batch size too large"
• "queue batch failed too large"
• "maxbatchsize consumer failed"

Why it happens

Batches multiply the handler's per-message cost by the batch size, and the product must fit in the worker's time and memory limits. Raising maxbatchsize for throughput without measuring the handler turns the consumer into a batch-sized failure. The setting is a capacity contract.

Edge cases

• the product of batch size and per-message time is what matters, not either alone
• poison messages fail whole batches; the dead-letter queue is essential
• batch timeouts interact with maxbatchtimeout; tune both together

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_xxCsKknAKwAcPbLfY3qZsg