hyperledger/fabric · info

SyncBuffer stopping, channel: %s

Error message

SyncBuffer stopping, channel: %s

What it means

HandleBlock blocks trying to place a fetched block onto SyncBuffer's internal channel; if the buffer is shutting down (stopCh closed) the send is abandoned and this error reports that the SyncBuffer is stopping. It is a normal consequence of synchronization being cancelled (shutdown, reconfiguration, view change), not data corruption.

Source

Thrown at orderer/consensus/smartbft/sync_buffer.go:42

		capacity = 10
	}
	return &SyncBuffer{
		blockCh: make(chan *common.Block, capacity),
		stopCh:  make(chan struct{}),
	}
}

// HandleBlock gives the block to the next stage of processing after fetching it from a remote orderer.
func (sb *SyncBuffer) HandleBlock(channelID string, block *common.Block) error {
	if block == nil || block.Header == nil {
		return errors.Errorf("empty block or block header, channel: %s", channelID)
	}

	select {
	case sb.blockCh <- block:
		return nil
	case <-sb.stopCh:
		return errors.Errorf("SyncBuffer stopping, channel: %s", channelID)
	}
}

func (sb *SyncBuffer) PullBlock(seq uint64) *common.Block {
	var block *common.Block
	for {
		select {
		case block = <-sb.blockCh:
			if block == nil || block.Header == nil {
				return nil
			}
			if block.GetHeader().GetNumber() == seq {
				return block
			}
			if block.GetHeader().GetNumber() < seq {
				continue
			}
			if block.GetHeader().GetNumber() > seq {

View on GitHub (pinned to 2736b63f8f)

Solutions

1. No action needed if it appears during shutdown/restart — it is expected cancellation noise.
2. If frequent, investigate why synchronization keeps being cancelled (chain restarts, flapping leader, channel churn) via orderer logs.
3. Ensure graceful orderer shutdown ordering (stop services before killing the process) to minimize in-flight sync cancellations.
4. Check for crash loops or channel join/remove automation racing with sync and serialize those operations.

Example fix

// before
// killing orderer during sync
kill -9 <orderer-pid>

// after
// graceful stop
osnadmin channel join/remove settled first
systemctl stop fabric-orderer

err := sb.HandleBlock(channelID, block)
if err != nil && strings.Contains(err.Error(), "SyncBuffer stopping") {
    // expected during shutdown: log at debug and exit cleanly
    logger.Debugf("sync aborted, buffer stopping: %v", err)
    return nil
}

When it happens

Trigger: A block arrives from the puller at the same moment the orderer/chain is shutting down or the sync loop is being stopped (e.g. channel halt, node restart, chain reconfiguration), closing stopCh while HandleBlock is mid-delivery.

Common situations: Orderer shutdown or restart while background synchronization is in flight; channel removal via the participation API during an active sync; a view/leader change cancelling an ongoing synchronization.

Related errors

• empty block or block header, channel: %s
• cannot get create BlockPuller
• consenter options type mismatch
• communication has been shut down
• failed to unmarshal BFT metadata configuration

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/4724c23af8e6e594. Report an issue: GitHub.