What causes "Compress block key %s: %s" in juicedata/juicefs?

Check the wrapped inner error (%s) to identify the root cause (corrupt data vs compressor failure).

Compress block key %s: %s

Error message

Compress block key %s: %s

What it means

During upload, the cached store compresses each block with the configured compressor. If Compress returns an error, upload aborts and wraps it as "Compress block key %s: %s", identifying the block key and the underlying compression failure. The block buffer is released either way, so the upload does not retry compression here.

Source

Thrown at pkg/chunk/cached_store.go:363

	sync := s != nil
	blen := len(block.Data)
	bufSize := store.compressor.CompressBound(blen)
	var buf *Page
	if bufSize > blen {
		buf = NewOffPage(bufSize)
	} else {
		buf = block
		buf.Acquire()
	}
	defer buf.Release()
	if sync && (blen < store.conf.BlockSize || store.conf.CacheLargeWrite) {
		// block will be freed after written into disk
		store.bcache.cache(key, block, false, false)
	}
	n, err := store.compressor.Compress(buf.Data, block.Data)
	block.Release()
	if err != nil {
		return fmt.Errorf("Compress block key %s: %s", key, err)
	}
	buf.Data = buf.Data[:n]

	try, max := 0, 3
	if sync {
		max = store.conf.MaxRetries + 1
	}
	for ; try < max; try++ {
		time.Sleep(time.Second * time.Duration(try*try))
		if s != nil && s.uploadError != nil {
			err = fmt.Errorf("(cancelled) upload block %s: %s (after %d tries)", key, err, try)
			break
		}
		if err = store.put(ctx, key, buf); err == nil {
			break
		}
		logger.Debugf("Upload %s: %s (try %d)", key, err, try+1)
	}

View on GitHub (pinned to c9a67b23e8)

Solutions

Check the wrapped inner error (%s) to identify the root cause (corrupt data vs compressor failure).
Switch to a different --compress setting (e.g. 'lz4' or 'none') in the volume format and re-test the workload.
Verify staging/cache disk integrity (fsck, SMART) — corruption is a common root cause; re-upload the affected block from source data.
Upgrade JuiceFS: compressor bugs have been fixed in past releases; ensure client versions are consistent.

Example fix

// before
juicefs format --compress zstd sqlite3://test.db myjfs
// after (fallback to widely-supported algorithm)
juicefs format --compress lz4 sqlite3://test.db myjfs

Defensive patterns

Strategy: try-catch

Try / catch

if err := storeUpload(ctx, key, buf); err != nil {
    if strings.HasPrefix(err.Error(), "Compress block key") {
        // check wrapped cause; consider re-reading block or changing --compress
    }
}

Prevention

Choose a stable, well-supported compressor in volume format
Monitor disk health — corruption is a common trigger
Keep client versions consistent across the cluster

When it happens

Trigger: A block fails to compress — typically corrupt or invalid input data for the configured compressor (e.g. zstd/lz4 failing on malformed input), a compressor misconfiguration, or a broken compressor implementation returning an unexpected result.

Common situations: --compress option set to an algorithm whose library fails on some data; corrupted staging/cache files on a failing disk; version mismatch where a compressor registered under a name behaves differently.

Related errors

AI-assisted analysis of juicedata/juicefs@c9a67b23e8 (2026-09-06). Data as JSON: /api/errors/ceed61b359d3695c. Report an issue: GitHub.