lightning: return 0 early on empty parquet files (pingcap#52519)

close pingcap#52518

pkg/lightning/mydump/loader.go

@@ -826,7 +826,7 @@ func SampleFileCompressRatio(ctx context.Context, fileMeta SourceFileMeta, store
 // SampleParquetDataSize samples the data size of the parquet file.
 func SampleParquetDataSize(ctx context.Context, fileMeta SourceFileMeta, store storage.ExternalStorage) (int64, error) {
 	totalRowCount, err := ReadParquetFileRowCountByFile(ctx, store, fileMeta)
-	if err != nil {
+	if totalRowCount == 0 || err != nil {
 		return 0, err
 	}
 

pkg/lightning/mydump/loader_test.go

@@ -1108,7 +1108,7 @@ func TestSampleFileCompressRatio(t *testing.T) {
 	require.InDelta(t, ratio, 5000.0/float64(bf.Len()), 1e-5)
 }
 
-func TestSampleParquetDataSize(t *testing.T) {
+func testSampleParquetDataSize(t *testing.T, count int) {
 	s := newTestMydumpLoaderSuite(t)
 	store, err := storage.NewLocalStorage(s.sourceDir)
 	require.NoError(t, err)
@@ -1133,7 +1133,7 @@ func TestSampleParquetDataSize(t *testing.T) {
 	t.Logf("seed: %d. To reproduce the random behaviour, manually set `rand.New(rand.NewSource(seed))`", seed)
 	rnd := rand.New(rand.NewSource(seed))
 	totalRowSize := 0
-	for i := 0; i < 1000; i++ {
+	for i := 0; i < count; i++ {
 		kl := rnd.Intn(20) + 1
 		key := make([]byte, kl)
 		kl, err = rnd.Read(key)
@@ -1167,6 +1167,11 @@ func TestSampleParquetDataSize(t *testing.T) {
 	require.InDelta(t, totalRowSize, size, float64(totalRowSize)/10)
 }
 
+func TestSampleParquetDataSize(t *testing.T) {
+	t.Run("count=1000", func(t *testing.T) { testSampleParquetDataSize(t, 1000) })
+	t.Run("count=0", func(t *testing.T) { testSampleParquetDataSize(t, 0) })
+}
+
 func TestSetupOptions(t *testing.T) {
 	// those functions are only used in other components, add this to avoid they
 	// be deleted mistakenly.