perf(clickhouse): P0 write path — remove heartbeat DELETE, batchwriter MinBatchSize, tune chwriter

internal/db/batchwriter/config.go

@@ -9,9 +9,10 @@ import (
 )
 
 const (
-	defaultQueueSize    = 10_000
-	defaultMaxBatchSize = 1_000
-	defaultFlushEvery   = time.Second
+	defaultQueueSize     = 10_000
+	defaultMaxBatchSize  = 1_000
+	defaultMinBatchSize  = 50
+	defaultFlushEvery    = time.Second
 )
 
 // Config controls queue capacity and flush thresholds for a Writer instance.
@@ -25,6 +26,10 @@ type Config struct {
 	// MaxBatchSize triggers a flush when the in-memory batch reaches this count.
 	MaxBatchSize int
 
+	// MinBatchSize is the minimum in-memory batch size for time-based flushes.
+	// Zero disables the threshold and preserves legacy interval flush behavior.
+	MinBatchSize int
+
 	// FlushInterval triggers a time-based flush even when the batch is smaller.
 	FlushInterval time.Duration
 }
@@ -34,6 +39,7 @@ func DefaultConfig() Config {
 	return Config{
 		QueueSize:     defaultQueueSize,
 		MaxBatchSize:  defaultMaxBatchSize,
+		MinBatchSize:  defaultMinBatchSize,
 		FlushInterval: defaultFlushEvery,
 	}
 }
@@ -45,6 +51,9 @@ func (c Config) validate() error {
 	if c.MaxBatchSize <= 0 {
 		return fmt.Errorf("batchwriter: max batch size must be positive")
 	}
+	if c.MinBatchSize < 0 {
+		return fmt.Errorf("batchwriter: min batch size must be non-negative")
+	}
 	if c.FlushInterval <= 0 {
 		return fmt.Errorf("batchwriter: flush interval must be positive")
 	}

internal/db/batchwriter/writer.go

@@ -202,7 +202,9 @@ func (w *Writer[T]) run() {
 				flush()
 			}
 		case <-ticker.C:
-			flush()
+			if len(batch) > 0 && (w.cfg.MinBatchSize == 0 || len(batch) >= w.cfg.MinBatchSize) {
+				flush()
+			}
 		}
 	}
 }

internal/db/batchwriter/writer_test.go

@@ -98,6 +98,7 @@ func TestWriterFlushesOnInterval(t *testing.T) {
 	)
 	cfg := DefaultConfig()
 	cfg.MaxBatchSize = 100
+	cfg.MinBatchSize = 0
 	cfg.FlushInterval = 20 * time.Millisecond
 
 	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
@@ -219,6 +220,112 @@ func TestWriterStopDrainsQueuedItems(t *testing.T) {
 	}
 }
 
+func TestWriterSkipsIntervalFlushBelowMinBatchSize(t *testing.T) {
+	t.Parallel()
+
+	var (
+		mu    sync.Mutex
+		batch []int
+	)
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 100
+	cfg.MinBatchSize = 5
+	cfg.FlushInterval = 20 * time.Millisecond
+
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		mu.Lock()
+		defer mu.Unlock()
+		batch = append([]int(nil), items...)
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		if err := writer.Stop(stopCtx); err != nil {
+			t.Fatalf("Stop() error = %v", err)
+		}
+	})
+
+	for i := range 3 {
+		if !writer.TryEnqueue(i + 1) {
+			t.Fatalf("TryEnqueue(%d) = false, want true", i+1)
+		}
+	}
+
+	time.Sleep(100 * time.Millisecond)
+
+	mu.Lock()
+	got := batch
+	mu.Unlock()
+
+	if len(got) != 0 {
+		t.Fatalf("interval flush with below-min batch = %v, want no flush", got)
+	}
+}
+
+func TestWriterFlushesOnIntervalWhenMinBatchSizeReached(t *testing.T) {
+	t.Parallel()
+
+	var (
+		mu    sync.Mutex
+		batch []int
+	)
+	cfg := DefaultConfig()
+	cfg.MaxBatchSize = 100
+	cfg.MinBatchSize = 3
+	cfg.FlushInterval = 20 * time.Millisecond
+
+	writer, err := New[int](cfg, func(_ context.Context, items []int) error {
+		mu.Lock()
+		defer mu.Unlock()
+		batch = append([]int(nil), items...)
+		return nil
+	})
+	if err != nil {
+		t.Fatalf("New() error = %v", err)
+	}
+
+	writer.Start(context.Background())
+	t.Cleanup(func() {
+		stopCtx, cancel := context.WithTimeout(context.Background(), time.Second)
+		defer cancel()
+		if err := writer.Stop(stopCtx); err != nil {
+			t.Fatalf("Stop() error = %v", err)
+		}
+	})
+
+	for i := range 3 {
+		if !writer.TryEnqueue(i + 1) {
+			t.Fatalf("TryEnqueue(%d) = false, want true", i+1)
+		}
+	}
+
+	deadline := time.Now().Add(time.Second)
+	for {
+		mu.Lock()
+		ready := len(batch) == 3
+		mu.Unlock()
+		if ready || time.Now().After(deadline) {
+			break
+		}
+		time.Sleep(5 * time.Millisecond)
+	}
+
+	mu.Lock()
+	got := batch
+	mu.Unlock()
+
+	want := []int{1, 2, 3}
+	if diff := cmp.Diff(want, got); diff != "" {
+		t.Fatalf("interval flush at min batch size mismatch (-want +got):\n%s", diff)
+	}
+}
+
 func TestWriterInvokesFlushErrorHandler(t *testing.T) {
 	t.Parallel()