Feature: Allow stream custom maxsize per batch

stream.go

@@ -62,6 +62,14 @@
 	// Note: Calls to ChooseKey are concurrent.
 	ChooseKey func(item *Item) bool
 
+	// MaxSize is the maximum allowed size of a stream batch. This is a soft limit
+	// as a single list that is still over the limit will have to be sent as is since it
+	// cannot be split further. This limit prevents the framework from creating batches
+	// so big that sending them causes issues (e.g running into the max size gRPC limit).
+	// If necessary, set it up before the Stream starts synchronisation
+	// This is not a concurrency-safe setting
+	MaxSize uint64
+
 	// KeyToList, similar to ChooseKey, is only invoked on the highest version of the value. It
 	// is upto the caller to iterate over the versions and generate zero, one or more KVs. It
 	// is expected that the user would advance the iterator to go through the versions of the
@@ -315,7 +323,7 @@
 			// Send the batch immediately if it already exceeds the maximum allowed size.
 			// If the size of the batch exceeds maxStreamSize, break from the loop to
 			// avoid creating a batch that is so big that certain limits are reached.
-			if batch.LenNoPadding() > int(maxStreamSize) {
+			if batch.LenNoPadding() > int(st.MaxSize) {
 				break loop
 			}
 			select {
@@ -452,6 +460,7 @@
 		db:        db,
 		NumGo:     db.opt.NumGoroutines,
 		LogPrefix: "Badger.Stream",
+		MaxSize:   maxStreamSize,
 	}
 }
 

stream_test.go

@@ -171,6 +171,68 @@ func TestStream(t *testing.T) {
 	require.NoError(t, db.Close())
 }
 
+
+func TestStreamMaxSize(t *testing.T) {
+	if !*manual {
+		t.Skip("Skipping test meant to be run manually.")
+		return
+	}
+	// Set the maxStreamSize to 1MB for the duration of the test so that the it can use a smaller
+	// dataset than it would otherwise need.
+	originalMaxStreamSize := maxStreamSize
+	maxStreamSize = 1 << 20
+	defer func() {
+		maxStreamSize = originalMaxStreamSize
+	}()
+
+	testSize := int(1e6)
+	dir, err := os.MkdirTemp("", "badger-big-test")
+	require.NoError(t, err)
+	defer removeDir(dir)
+
+	db, err := OpenManaged(DefaultOptions(dir))
+	require.NoError(t, err)
+
+	var count int
+	wb := db.NewWriteBatchAt(5)
+	for _, prefix := range []string{"p0", "p1", "p2"} {
+		for i := 1; i <= testSize; i++ {
+			require.NoError(t, wb.SetEntry(NewEntry(keyWithPrefix(prefix, i), value(i))))
+			count++
+		}
+	}
+	require.NoError(t, wb.Flush())
+
+	stream := db.NewStreamAt(math.MaxUint64)
+	stream.LogPrefix = "Testing"
+	c := &collector{}
+	stream.Send = c.Send
+
+	// default value
+	require.Equal(t, stream.MaxSize, maxStreamSize)
+
+	// reset maxsize
+	stream.MaxSize = 1024 * 1024 * 50
+
+	// Test case 1. Retrieve everything.
+	err = stream.Orchestrate(ctxb)
+	require.NoError(t, err)
+	require.Equal(t, 3*testSize, len(c.kv), "Expected 30000. Got: %d", len(c.kv))
+
+	m := make(map[string]int)
+	for _, kv := range c.kv {
+		prefix, ki := keyToInt(kv.Key)
+		expected := value(ki)
+		require.Equal(t, expected, kv.Value)
+		m[prefix]++
+	}
+	require.Equal(t, 3, len(m))
+	for pred, count := range m {
+		require.Equal(t, testSize, count, "Count mismatch for pred: %s", pred)
+	}
+	require.NoError(t, db.Close())
+}
+
 func TestStreamWithThreadId(t *testing.T) {
 	dir, err := os.MkdirTemp("", "badger-test")
 	require.NoError(t, err)