MyCATApache/Mycat-Server · error · IllegalArgumentException

n must be > 0

Error message

n must be > 0

What it means

MultiProducerSequencer.next(n) claims n consecutive sequences for a publisher. It validates n >= 1 and throws IllegalArgumentException for n < 1, since claiming zero or a negative number of slots is meaningless. This is the blocking claim path; the argument check happens before any spinning on the gating sequences.

Solutions

1. Only call next() with n >= 1; skip the call entirely for empty batches
2. Clamp the requested count: Math.max(1, n) if a claim is always required
3. Fix the batch computation so batchSize reflects the actual number of events to publish

Example fix

// before
int batchSize = endIndex - startIndex;
long seq = sequencer.next(batchSize);
// after
int batchSize = endIndex - startIndex;
if (batchSize <= 0) return;
long seq = sequencer.next(batchSize);

if (n >= 1) { long seq = sequencer.next(n); }

boolean canClaim(int n) { return n >= 1; }

try { long seq = sequencer.next(n); } catch (IllegalArgumentException e) { log.error("invalid claim count", e); }

When it happens

Trigger: Calling sequencer.next(0) or next(-1) (or RingBuffer.next(0)) directly, or via a batch publisher whose batchSize was computed as 0 or negative (e.g. empty-batch subtraction).

Common situations: Batching logic computing batchSize = end - start when end == start; config where minBatchSize defaults to 0; off-by-one in loop that publishes in chunks.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• bufferSize must not be less than 1
• bufferSize must be a power of 2
• n must be > 0
• bufferSize must not be less than 1
• bufferSize must be a power of 2

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/8425b0e741de0e6a. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/memory/unsafe/ringbuffer/producer/MultiProducerSequencer.java:183

        long produced = cursor.get();
        return getBufferSize() - (produced - consumed);
    }

    @Override
    public long next() {
        return next(1);
    }

    /**
     * 用于多个生产者抢占n个RingBuffer槽用于生产Event
     *
     * @param n
     * @return
     */
    @Override
    public long next(int n) {
        if (n < 1) {
            throw new IllegalArgumentException("n must be > 0");
        }

        long current;
        long next;

        do {
            //首先通过缓存判断空间是否足够
            current = cursor.get();
            next = current + n;

            long wrapPoint = next - bufferSize;
            long cachedGatingSequence = gatingSequenceCache.get();
            //如果缓存不满足
            if (wrapPoint > cachedGatingSequence || cachedGatingSequence > current) {
                //重新获取最小的
                long gatingSequence = Util.getMinimumSequence(gatingSequences, current);
                //如果空间不足，则唤醒消费者消费，并让出CPU
                if (wrapPoint > gatingSequence) {

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