Function TestDB_MaxSizeExceededDoesNotGrow

db_test.go:1660–1748

Ensure that on Windows, mmap never expands the file speculatively via InitialMmapSize, and that the database remains fully usable after such an open. https://github.com/etcd-io/bbolt/issues/928

(t *testing.T)

// InitialMmapSize, and that the database remains fully usable after such an
// open. https://github.com/etcd-io/bbolt/issues/928
func TestDB_MaxSizeExceededDoesNotGrow(t *testing.T) {
	if runtime.GOOS != "windows" {
		t.SkipNow()
	}

	// Build a filled database to use as the base for all sub-tests.
	// 4 MiB allocation jumps, 2000 × 1 KB entries → file lands at ~4 MiB.
	base := createFilledDB(t, nil, 4*1024*1024, 2000)
	basePath := base.Path()
	require.NoError(t, base.Close())

	baseSize := fileSize(basePath)
	require.Greater(t, baseSize, int64(1024*1024), "base DB too small for test: %d", baseSize)

	// copyDB snapshots the base file into a fresh temp path so each sub-test
	// gets an independent copy.
	copyDB := func(t *testing.T) string {
		t.Helper()
		data, err := os.ReadFile(basePath)
		require.NoError(t, err)
		dst := filepath.Join(t.TempDir(), "db")
		require.NoError(t, os.WriteFile(dst, data, 0600))
		return dst
	}

	testCases := []struct {
		name            string
		initialMmapSize int // 0 means unset
		maxSize         int // 0 means unset
		// expected file size after re-open (0 means "same as baseSize")
		wantSize    int64
		wantOpenErr error
	}{
		{
			// On Windows, mmap expands the file to the mapped size immediately.
			// When InitialMmapSize > MaxSize, the mmap call itself would grow the
			// file past MaxSize, so Open is rejected with ErrMaxSizeReached rather
			// than silently exceeding the limit.
			name:            "InitialMmapSize larger than file does not grow",
			initialMmapSize: int(baseSize) * 2,
			maxSize:         1,
			wantSize:        baseSize,
			wantOpenErr:     berrors.ErrMaxSizeReached,
		},
		{
			name:            "InitialMmapSize equal to file size does not grow",
			initialMmapSize: int(baseSize),
			maxSize:         1,
			wantSize:        baseSize,
		},
		{
			name:            "InitialMmapSize smaller than file size does not shrink",
			initialMmapSize: int(baseSize) / 2,
			maxSize:         1,
			wantSize:        baseSize,
		},
		{
			name:            "no InitialMmapSize does not grow",