[Bugfix] Broken Heartbeat system in Row Streamer (#18390)

Signed-off-by: siddharth16396 <siddharth16396@gmail.com>

Author: vitess-bot[bot]

go/vt/vttablet/tabletserver/vstreamer/rowstreamer.go

@@ -362,11 +362,13 @@ func (rs *rowStreamer) streamQuery(send func(*binlogdatapb.VStreamRowsResponse)
 	heartbeatTicker := time.NewTicker(rowStreamertHeartbeatInterval)
 	defer heartbeatTicker.Stop()
 	go func() {
-		select {
-		case <-rs.ctx.Done():
-			return
-		case <-heartbeatTicker.C:
-			safeSend(&binlogdatapb.VStreamRowsResponse{Heartbeat: true})
+		for {
+			select {
+			case <-rs.ctx.Done():
+				return
+			case <-heartbeatTicker.C:
+				safeSend(&binlogdatapb.VStreamRowsResponse{Heartbeat: true})
+			}
 		}
 	}()
 

go/vt/vttablet/tabletserver/vstreamer/rowstreamer_test.go

@@ -21,6 +21,7 @@ import (
 	"fmt"
 	"regexp"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 
@@ -432,6 +433,78 @@ func TestStreamRowsCancel(t *testing.T) {
 	}
 }
 
+func TestStreamRowsHeartbeat(t *testing.T) {
+	if testing.Short() {
+		t.Skip()
+	}
+
+	// Save original heartbeat interval and restore it after test
+	originalInterval := rowStreamertHeartbeatInterval
+	defer func() {
+		rowStreamertHeartbeatInterval = originalInterval
+	}()
+
+	// Set a very short heartbeat interval for testing (100ms)
+	rowStreamertHeartbeatInterval = 10 * time.Millisecond
+
+	execStatements(t, []string{
+		"create table t1(id int, val varchar(128), primary key(id))",
+		"insert into t1 values (1, 'test1')",
+		"insert into t1 values (2, 'test2')",
+		"insert into t1 values (3, 'test3')",
+		"insert into t1 values (4, 'test4')",
+		"insert into t1 values (5, 'test5')",
+	})
+
+	defer execStatements(t, []string{
+		"drop table t1",
+	})
+
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+
+	heartbeatCount := 0
+	dataReceived := false
+
+	var options binlogdatapb.VStreamOptions
+	options.ConfigOverrides = make(map[string]string)
+	options.ConfigOverrides["vstream_dynamic_packet_size"] = "false"
+	options.ConfigOverrides["vstream_packet_size"] = "10"
+
+	err := engine.StreamRows(ctx, "select * from t1", nil, func(rows *binlogdatapb.VStreamRowsResponse) error {
+		if rows.Heartbeat {
+			heartbeatCount++
+			// After receiving at least 3 heartbeats, we can be confident the fix is working
+			if heartbeatCount >= 3 {
+				cancel()
+				return nil
+			}
+		} else if len(rows.Rows) > 0 {
+			dataReceived = true
+		}
+		// Add a small delay to allow heartbeats to be sent
+		time.Sleep(50 * time.Millisecond)
+		return nil
+	}, &options)
+
+	// We expect context canceled error since we cancel after receiving heartbeats
+	if err != nil && err.Error() != "stream ended: context canceled" {
+		t.Errorf("unexpected error: %v", err)
+	}
+
+	// Verify we received data
+	if !dataReceived {
+		t.Error("expected to receive data rows")
+	}
+
+	// This is the critical test: we should receive multiple heartbeats
+	// Without the fix (missing for loop), we would only get 1 heartbeat
+	// With the fix, we should get at least 3 heartbeats
+	if heartbeatCount < 3 {
+		t.Errorf("expected at least 3 heartbeats, got %d. This indicates the heartbeat goroutine is not running continuously", heartbeatCount)
+	}
+}
+
 func checkStream(t *testing.T, query string, lastpk []sqltypes.Value, wantQuery string, wantStream []string) {
 	t.Helper()