Query serving: incorporate mirror query results in log stats, fix mir…

…ror query max lag bug (#16879)

Signed-off-by: Max Englander <[email protected]>

go/vt/vtgate/engine/fake_vcursor_test.go

@@ -445,9 +445,10 @@ type loggingVCursor struct {
 
 	parser *sqlparser.Parser
 
-	handleMirrorClonesFn   func(context.Context) VCursor
+	onMirrorClonesFn       func(context.Context) VCursor
 	onExecuteMultiShardFn  func(context.Context, Primitive, []*srvtopo.ResolvedShard, []*querypb.BoundQuery, bool, bool)
 	onStreamExecuteMultiFn func(context.Context, Primitive, string, []*srvtopo.ResolvedShard, []map[string]*querypb.BindVariable, bool, bool, func(*sqltypes.Result) error)
+	onRecordMirrorStatsFn  func(time.Duration, time.Duration, error)
 }
 
 func (f *loggingVCursor) HasCreatedTempTable() {
@@ -564,8 +565,8 @@ func (f *loggingVCursor) CloneForReplicaWarming(ctx context.Context) VCursor {
 }
 
 func (f *loggingVCursor) CloneForMirroring(ctx context.Context) VCursor {
-	if f.handleMirrorClonesFn != nil {
-		return f.handleMirrorClonesFn(ctx)
+	if f.onMirrorClonesFn != nil {
+		return f.onMirrorClonesFn(ctx)
 	}
 	panic("no mirror clones available")
 }
@@ -886,6 +887,12 @@ func (t *loggingVCursor) SQLParser() *sqlparser.Parser {
 	return t.parser
 }
 
+func (t *loggingVCursor) RecordMirrorStats(sourceExecTime, targetExecTime time.Duration, targetErr error) {
+	if t.onRecordMirrorStatsFn != nil {
+		t.onRecordMirrorStatsFn(sourceExecTime, targetExecTime, targetErr)
+	}
+}
+
 func (t *noopVCursor) VExplainLogging() {}
 func (t *noopVCursor) DisableLogging()  {}
 func (t *noopVCursor) GetVExplainLogs() []ExecuteEntry {
@@ -896,6 +903,10 @@ func (t *noopVCursor) GetLogs() ([]ExecuteEntry, error) {
 	return nil, nil
 }
 
+// RecordMirrorStats implements VCursor.
+func (t *noopVCursor) RecordMirrorStats(sourceExecTime, targetExecTime time.Duration, targetErr error) {
+}
+
 func expectResult(t *testing.T, result, want *sqltypes.Result) {
 	t.Helper()
 	fieldsResult := fmt.Sprintf("%v", result.Fields)

go/vt/vtgate/engine/mirror.go

@@ -23,8 +23,12 @@ import (
 
 	"vitess.io/vitess/go/sqltypes"
 	querypb "vitess.io/vitess/go/vt/proto/query"
+	"vitess.io/vitess/go/vt/proto/vtrpc"
+	"vitess.io/vitess/go/vt/vterrors"
 )
 
+var errMirrorTargetQueryTookTooLong = vterrors.Errorf(vtrpc.Code_ABORTED, "Mirror target query took too long")
+
 type (
 	// percentBasedMirror represents the instructions to execute an
 	// authoritative primitive and, based on whether a die-roll exceeds a
@@ -34,6 +38,11 @@ type (
 		primitive Primitive
 		target    Primitive
 	}
+
+	mirrorResult struct {
+		execTime time.Duration
+		err      error
+	}
 )
 
 const (
@@ -74,26 +83,44 @@ func (m *percentBasedMirror) TryExecute(ctx context.Context, vcursor VCursor, bi
 		return vcursor.ExecutePrimitive(ctx, m.primitive, bindVars, wantfields)
 	}
 
-	mirrorCh := make(chan any)
-	mirrorCtx, mirrorCtxCancel := context.WithTimeout(ctx, maxMirrorTargetLag)
+	mirrorCh := make(chan mirrorResult, 1)
+	mirrorCtx, mirrorCtxCancel := context.WithCancel(ctx)
 	defer mirrorCtxCancel()
 
 	go func() {
-		defer close(mirrorCh)
 		mirrorVCursor := vcursor.CloneForMirroring(mirrorCtx)
-		// TODO(maxeng) handle error.
-		_, _ = mirrorVCursor.ExecutePrimitive(mirrorCtx, m.target, bindVars, wantfields)
+		targetStartTime := time.Now()
+		_, targetErr := mirrorVCursor.ExecutePrimitive(mirrorCtx, m.target, bindVars, wantfields)
+		mirrorCh <- mirrorResult{
+			execTime: time.Since(targetStartTime),
+			err:      targetErr,
+		}
 	}()
 
+	var (
+		sourceExecTime, targetExecTime time.Duration
+		targetErr                      error
+	)
+
+	sourceStartTime := time.Now()
 	r, err := vcursor.ExecutePrimitive(ctx, m.primitive, bindVars, wantfields)
+	sourceExecTime = time.Since(sourceStartTime)
 
+	// Cancel the mirror context if it continues executing too long.
 	select {
-	case <-mirrorCh:
-		// Mirroring completed within the allowed time.
-	case <-mirrorCtx.Done():
-		// Mirroring took too long and was canceled.
+	case r := <-mirrorCh:
+		// Mirror target finished on time.
+		targetExecTime = r.execTime
+		targetErr = r.err
+	case <-time.After(maxMirrorTargetLag):
+		// Mirror target took too long.
+		mirrorCtxCancel()
+		targetExecTime = sourceExecTime + maxMirrorTargetLag
+		targetErr = errMirrorTargetQueryTookTooLong
 	}
 
+	vcursor.RecordMirrorStats(sourceExecTime, targetExecTime, targetErr)
+
 	return r, err
 }
 
@@ -102,30 +129,46 @@ func (m *percentBasedMirror) TryStreamExecute(ctx context.Context, vcursor VCurs
 		return vcursor.StreamExecutePrimitive(ctx, m.primitive, bindVars, wantfields, callback)
 	}
 
-	mirrorCh := make(chan any)
-	mirrorCtx, mirrorCtxCancel := context.WithTimeout(ctx, maxMirrorTargetLag)
+	mirrorCh := make(chan mirrorResult, 1)
+	mirrorCtx, mirrorCtxCancel := context.WithCancel(ctx)
 	defer mirrorCtxCancel()
 
 	go func() {
-		defer close(mirrorCh)
 		mirrorVCursor := vcursor.CloneForMirroring(mirrorCtx)
-		// TODO(maxeng) handle error.
-		_ = mirrorVCursor.StreamExecutePrimitive(
-			mirrorCtx, m.target, bindVars, wantfields, func(_ *sqltypes.Result,
-			) error {
-				return nil
-			})
+		mirrorStartTime := time.Now()
+		targetErr := mirrorVCursor.StreamExecutePrimitive(mirrorCtx, m.target, bindVars, wantfields, func(_ *sqltypes.Result) error {
+			return nil
+		})
+		mirrorCh <- mirrorResult{
+			execTime: time.Since(mirrorStartTime),
+			err:      targetErr,
+		}
 	}()
 
+	var (
+		sourceExecTime, targetExecTime time.Duration
+		targetErr                      error
+	)
+
+	sourceStartTime := time.Now()
 	err := vcursor.StreamExecutePrimitive(ctx, m.primitive, bindVars, wantfields, callback)
+	sourceExecTime = time.Since(sourceStartTime)
 
+	// Cancel the mirror context if it continues executing too long.
 	select {
-	case <-mirrorCh:
-		// Mirroring completed within the allowed time.
-	case <-mirrorCtx.Done():
-		// Mirroring took too long and was canceled.
+	case r := <-mirrorCh:
+		// Mirror target finished on time.
+		targetExecTime = r.execTime
+		targetErr = r.err
+	case <-time.After(maxMirrorTargetLag):
+		// Mirror target took too long.
+		mirrorCtxCancel()
+		targetExecTime = sourceExecTime + maxMirrorTargetLag
+		targetErr = errMirrorTargetQueryTookTooLong
 	}
 
+	vcursor.RecordMirrorStats(sourceExecTime, targetExecTime, targetErr)
+
 	return err
 }