juicedata/juicefs · error

size of first key shold be 5, but got %v

Error message

size of first key shold be 5, but got %v

What it means

Raised in the objbench 'list objects' filesystem case: the second listed entry is the just-uploaded 5-byte object 'test', so its Size() must be 5, but the backend reported a different size. This asserts that listing returns accurate object sizes (typo 'shold' is in the source message).

Source

Thrown at cmd/objbench.go:905

		}
		defer blob.Delete(ctx, key) //nolint:errcheck
		if isFileSystem {
			objs, err := listAll(ctx, blob, "", "", 2)
			if err == nil {
				if len(objs) != 2 {
					return fmt.Errorf("list should return 2 keys, but got %d", len(objs))
				}
				if objs[0].Key() != "" {
					return fmt.Errorf("first key should be empty string, but got %s", objs[0].Key())
				}
				if objs[0].Size() != 0 {
					return fmt.Errorf("first object size should be 0, but got %d", objs[0].Size())
				}
				if objs[1].Key() != key {
					return fmt.Errorf("first key should be test, but got %s", objs[1].Key())
				}
				if objs[1].Size() != 5 {
					return fmt.Errorf("size of first key shold be 5, but got %v", objs[1].Size())
				}
				now := time.Now()
				if objs[1].Mtime().Before(now.Add(-30*time.Second)) || objs[1].Mtime().After(now.Add(time.Second*30)) {
					return fmt.Errorf("mtime of key should be within 30 seconds, but got %s", objs[1].Mtime().Sub(now))
				}
			} else {
				return fmt.Errorf("list failed: %s", err)
			}

			objs, err = listAll(ctx, blob, "", "test2", 1)
			if err != nil {
				return fmt.Errorf("list failed: %s", err)
			} else if len(objs) != 0 {
				return fmt.Errorf("list should not return anything, but got %d", len(objs))
			}
		} else {
			objs, err2 := listAll(ctx, blob, "", "", 1)
			if err2 == nil {

View on GitHub (pinned to c9a67b23e8)

Solutions

1. Fix the backend's List to populate Size() from the file/object's actual length (5 for "hello").
2. Verify Put is fully flushed before List runs (no async write-behind reporting wrong sizes).
3. Compare with the reference file:// implementation in pkg/object.
4. Clear size/attr caches on the filesystem-backed store.
5. Rerun objbench to confirm.

Example fix

// before
return &entry{key: name, size: 0}, nil // size never populated
// after
fi, _ := os.Stat(path)
return &entry{key: name, size: fi.Size()}, nil

objs, _ := listAll(ctx, blob, "", "", 2)
if len(objs) > 1 && objs[1].Key() == key && objs[1].Size() != 5 {
    log.Printf("reported size %d, want 5", objs[1].Size())
}

func sizeMatches(o object.Object, want uint64) bool {
    return o.Size() == want
}

if s := objs[1].Size(); s != 5 {
    log.Printf("list size %d != put size 5; check flush/caching", s)
}

When it happens

Trigger: After Put of []byte("hello"), listAll returns the key correctly but objs[1].Size() != 5 — e.g. the backend reports the directory stat size, a block-aligned size, 0, or a stale cached size.

Common situations: Custom file backend using os.Stat's Size() on a directory or returning allocated size; a backend whose List fills size from a stale cache; backends that don't populate size in list results at all; uploads still in flight/flushed asynchronously.

Understand the failure class

Background: "invalid response format", "malformed payload", "missing data field": when an API returns 200 but the response shape is wrong — this error's family across 23 libraries.

Related errors

• first object size should be 0, but got %d
• list should return 2 keys, but got %d
• first key should be empty string, but got %s
• first key should be test, but got %s
• list failed: %s

AI-assisted analysis of juicedata/juicefs@c9a67b23e8 (2026-09-06). Data as JSON: /api/errors/41631a7a5325ece6. Report an issue: GitHub.