Refactor remote storage querier handling

* Decouple remote client from ReadRecent feature.
* Separate remote read filter into a small, testable function.
* Use storage.Queryable interface to compose independent
  functionalities.

storage/remote/client.go

@@ -37,18 +37,16 @@ const maxErrMsgLen = 256
 
 // Client allows reading and writing from/to a remote HTTP endpoint.
 type Client struct {
-	index      int // Used to differentiate metrics.
-	url        *config.URL
-	client     *http.Client
-	timeout    time.Duration
-	readRecent bool
+	index   int // Used to differentiate clients in metrics.
+	url     *config.URL
+	client  *http.Client
+	timeout time.Duration
 }
 
 // ClientConfig configures a Client.
 type ClientConfig struct {
 	URL              *config.URL
 	Timeout          model.Duration
-	ReadRecent       bool
 	HTTPClientConfig config.HTTPClientConfig
 }
 
@@ -60,11 +58,10 @@ func NewClient(index int, conf *ClientConfig) (*Client, error) {
 	}
 
 	return &Client{
-		index:      index,
-		url:        conf.URL,
-		client:     httpClient,
-		timeout:    time.Duration(conf.Timeout),
-		readRecent: conf.ReadRecent,
+		index:   index,
+		url:     conf.URL,
+		client:  httpClient,
+		timeout: time.Duration(conf.Timeout),
 	}, nil
 }
 

storage/remote/codec.go

@@ -158,6 +158,12 @@ func FromQueryResult(res *prompb.QueryResult) storage.SeriesSet {
 	}
 }
 
+type byLabel []storage.Series
+
+func (a byLabel) Len() int           { return len(a) }
+func (a byLabel) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+func (a byLabel) Less(i, j int) bool { return labels.Compare(a[i].Labels(), a[j].Labels()) < 0 }
+
 // errSeriesSet implements storage.SeriesSet, just returning an error.
 type errSeriesSet struct {
 	err error

storage/remote/read.go

@@ -21,55 +21,30 @@ import (
 	"github.com/prometheus/prometheus/storage"
 )
 
-// Querier returns a new Querier on the storage.
-func (r *Storage) Querier(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
-	r.mtx.Lock()
-	defer r.mtx.Unlock()
-
-	queriers := make([]storage.Querier, 0, len(r.clients))
-	localStartTime, err := r.localStartTimeCallback()
-	if err != nil {
-		return nil, err
-	}
-	for _, c := range r.clients {
-		cmaxt := maxt
-		if !c.readRecent {
-			// Avoid queries whose timerange is later than the first timestamp in local DB.
-			if mint > localStartTime {
-				continue
-			}
-			// Query only samples older than the first timestamp in local DB.
-			if maxt > localStartTime {
-				cmaxt = localStartTime
-			}
-		}
-		queriers = append(queriers, &querier{
-			ctx:            ctx,
-			mint:           mint,
-			maxt:           cmaxt,
-			client:         c,
-			externalLabels: r.externalLabels,
-		})
-	}
-	return newMergeQueriers(queriers), nil
+// QueryableClient returns a storage.Queryable which queries the given
+// Client to select series sets.
+func QueryableClient(c *Client) storage.Queryable {
+	return storage.QueryableFunc(func(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
+		return &querier{
+			ctx:    ctx,
+			mint:   mint,
+			maxt:   maxt,
+			client: c,
+		}, nil
+	})
 }
 
-// Store it in variable to make it mockable in tests since a mergeQuerier is not publicly exposed.
-var newMergeQueriers = storage.NewMergeQuerier
-
-// Querier is an adapter to make a Client usable as a storage.Querier.
+// querier is an adapter to make a Client usable as a storage.Querier.
 type querier struct {
-	ctx            context.Context
-	mint, maxt     int64
-	client         *Client
-	externalLabels model.LabelSet
+	ctx        context.Context
+	mint, maxt int64
+	client     *Client
 }
 
-// Select returns a set of series that matches the given label matchers.
+// Select implements storage.Querier and uses the given matchers to read series
+// sets from the Client.
 func (q *querier) Select(matchers ...*labels.Matcher) storage.SeriesSet {
-	m, added := q.addExternalLabels(matchers)
-
-	query, err := ToQuery(q.mint, q.maxt, m)
+	query, err := ToQuery(q.mint, q.maxt, matchers)
 	if err != nil {
 		return errSeriesSet{err: err}
 	}
@@ -79,40 +54,83 @@ func (q *querier) Select(matchers ...*labels.Matcher) storage.SeriesSet {
 		return errSeriesSet{err: err}
 	}
 
-	seriesSet := FromQueryResult(res)
-
-	return newSeriesSetFilter(seriesSet, added)
+	return FromQueryResult(res)
 }
 
-type byLabel []storage.Series
-
-func (a byLabel) Len() int           { return len(a) }
-func (a byLabel) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
-func (a byLabel) Less(i, j int) bool { return labels.Compare(a[i].Labels(), a[j].Labels()) < 0 }
-
-// LabelValues returns all potential values for a label name.
+// LabelValues implements storage.Querier and is a noop.
 func (q *querier) LabelValues(name string) ([]string, error) {
 	// TODO implement?
 	return nil, nil
 }
 
-// Close releases the resources of the Querier.
+// Close implements storage.Querier and is a noop.
 func (q *querier) Close() error {
 	return nil
 }
 
+// ExternablLabelsHandler returns a storage.Queryable which creates a
+// externalLabelsQuerier.
+func ExternablLabelsHandler(next storage.Queryable, externalLabels model.LabelSet) storage.Queryable {
+	return storage.QueryableFunc(func(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
+		q, err := next.Querier(ctx, mint, maxt)
+		if err != nil {
+			return nil, err
+		}
+		return &externalLabelsQuerier{Querier: q, externalLabels: externalLabels}, nil
+	})
+}
+
+// externalLabelsQuerier is a querier which ensures that Select() results match
+// the configured external labels.
+type externalLabelsQuerier struct {
+	storage.Querier
+
+	externalLabels model.LabelSet
+}
+
+// Select adds equality matchers for all external labels to the list of matchers
+// before calling the wrapped storage.Queryable. The added external labels are
+// removed from the returned series sets.
+func (q externalLabelsQuerier) Select(matchers ...*labels.Matcher) storage.SeriesSet {
+	m, added := q.addExternalLabels(matchers)
+	s := q.Querier.Select(m...)
+	return newSeriesSetFilter(s, added)
+}
+
+// PreferLocalStorageFilter returns a QueryableFunc which creates a NoopQuerier
+// if requested timeframe can be answered completely by the local TSDB, and
+// reduces maxt if the timeframe can be partially answered by TSDB.
+func PreferLocalStorageFilter(next storage.Queryable, cb startTimeCallback) storage.Queryable {
+	return storage.QueryableFunc(func(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
+		localStartTime, err := cb()
+		if err != nil {
+			return nil, err
+		}
+		cmaxt := maxt
+		// Avoid queries whose timerange is later than the first timestamp in local DB.
+		if mint > localStartTime {
+			return storage.NoopQuerier(), nil
+		}
+		// Query only samples older than the first timestamp in local DB.
+		if maxt > localStartTime {
+			cmaxt = localStartTime
+		}
+		return next.Querier(ctx, mint, cmaxt)
+	})
+}
+
 // addExternalLabels adds matchers for each external label. External labels
 // that already have a corresponding user-supplied matcher are skipped, as we
 // assume that the user explicitly wants to select a different value for them.
 // We return the new set of matchers, along with a map of labels for which
 // matchers were added, so that these can later be removed from the result
 // time series again.
-func (q *querier) addExternalLabels(matchers []*labels.Matcher) ([]*labels.Matcher, model.LabelSet) {
+func (q externalLabelsQuerier) addExternalLabels(ms []*labels.Matcher) ([]*labels.Matcher, model.LabelSet) {
 	el := make(model.LabelSet, len(q.externalLabels))
 	for k, v := range q.externalLabels {
 		el[k] = v
 	}
-	for _, m := range matchers {
+	for _, m := range ms {
 		if _, ok := el[model.LabelName(m.Name)]; ok {
 			delete(el, model.LabelName(m.Name))
 		}
@@ -122,9 +140,9 @@ func (q *querier) addExternalLabels(matchers []*labels.Matcher) ([]*labels.Match
 		if err != nil {
 			panic(err)
 		}
-		matchers = append(matchers, m)
+		ms = append(ms, m)
 	}
-	return matchers, el
+	return ms, el
 }
 
 func newSeriesSetFilter(ss storage.SeriesSet, toFilter model.LabelSet) storage.SeriesSet {

storage/remote/read_test.go

@@ -18,10 +18,8 @@ import (
 	"reflect"
 	"sort"
 	"testing"
-	"time"
 
 	"github.com/prometheus/common/model"
-	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/prompb"
 	"github.com/prometheus/prometheus/storage"
@@ -35,7 +33,22 @@ func mustNewLabelMatcher(mt labels.MatchType, name, val string) *labels.Matcher
 	return m
 }
 
-func TestAddExternalLabels(t *testing.T) {
+func TestExternalLabelsQuerierSelect(t *testing.T) {
+	matchers := []*labels.Matcher{
+		mustNewLabelMatcher(labels.MatchEqual, "job", "api-server"),
+	}
+	q := &externalLabelsQuerier{
+		Querier:        mockQuerier{},
+		externalLabels: model.LabelSet{"region": "europe"},
+	}
+
+	want := newSeriesSetFilter(mockSeriesSet{}, q.externalLabels)
+	if have := q.Select(matchers...); !reflect.DeepEqual(want, have) {
+		t.Errorf("expected series set %+v, got %+v", want, have)
+	}
+}
+
+func TestExternalLabelsQuerierAddExternalLabels(t *testing.T) {
 	tests := []struct {
 		el          model.LabelSet
 		inMatchers  []*labels.Matcher
@@ -80,10 +93,7 @@ func TestAddExternalLabels(t *testing.T) {
 	}
 
 	for i, test := range tests {
-		q := querier{
-			externalLabels: test.el,
-		}
-
+		q := &externalLabelsQuerier{Querier: mockQuerier{}, externalLabels: test.el}
 		matchers, added := q.addExternalLabels(test.inMatchers)
 
 		sort.Slice(test.outMatchers, func(i, j int) bool { return test.outMatchers[i].Name < test.outMatchers[j].Name })
@@ -133,58 +143,57 @@ func TestSeriesSetFilter(t *testing.T) {
 	}
 }
 
-type mockMergeQuerier struct{ queriersCount int }
+type testQuerier struct {
+	ctx        context.Context
+	mint, maxt int64
 
-func (*mockMergeQuerier) Select(...*labels.Matcher) storage.SeriesSet { return nil }
-func (*mockMergeQuerier) LabelValues(name string) ([]string, error)   { return nil, nil }
-func (*mockMergeQuerier) Close() error                                { return nil }
+	storage.Querier
+}
+
+func TestPreferLocalStorageFilter(t *testing.T) {
+	ctx := context.Background()
 
-func TestRemoteStorageQuerier(t *testing.T) {
 	tests := []struct {
-		localStartTime        int64
-		readRecentClients     []bool
-		mint                  int64
-		maxt                  int64
-		expectedQueriersCount int
+		localStartTime int64
+		mint           int64
+		maxt           int64
+		querier        storage.Querier
 	}{
 		{
-			localStartTime:    int64(20),
-			readRecentClients: []bool{true, true, false},
-			mint:              int64(0),
-			maxt:              int64(50),
-			expectedQueriersCount: 3,
+			localStartTime: int64(100),
+			mint:           int64(0),
+			maxt:           int64(50),
+			querier:        testQuerier{ctx: ctx, mint: 0, maxt: 50},
+		},
+		{
+			localStartTime: int64(20),
+			mint:           int64(0),
+			maxt:           int64(50),
+			querier:        testQuerier{ctx: ctx, mint: 0, maxt: 20},
 		},
 		{
-			localStartTime:    int64(20),
-			readRecentClients: []bool{true, true, false},
-			mint:              int64(30),
-			maxt:              int64(50),
-			expectedQueriersCount: 2,
+			localStartTime: int64(20),
+			mint:           int64(30),
+			maxt:           int64(50),
+			querier:        storage.NoopQuerier(),
 		},
 	}
 
 	for i, test := range tests {
-		s := NewStorage(nil, func() (int64, error) { return test.localStartTime, nil })
-		s.clients = []*Client{}
-		for _, readRecent := range test.readRecentClients {
-			c, _ := NewClient(0, &ClientConfig{
-				URL:              nil,
-				Timeout:          model.Duration(30 * time.Second),
-				HTTPClientConfig: config.HTTPClientConfig{},
-				ReadRecent:       readRecent,
-			})
-			s.clients = append(s.clients, c)
-		}
-		// overrides mergeQuerier to mockMergeQuerier so we can reflect its type
-		newMergeQueriers = func(queriers []storage.Querier) storage.Querier {
-			return &mockMergeQuerier{queriersCount: len(queriers)}
+		f := PreferLocalStorageFilter(
+			storage.QueryableFunc(func(ctx context.Context, mint, maxt int64) (storage.Querier, error) {
+				return testQuerier{ctx: ctx, mint: mint, maxt: maxt}, nil
+			}),
+			func() (int64, error) { return test.localStartTime, nil },
+		)
+
+		q, err := f.Querier(ctx, test.mint, test.maxt)
+		if err != nil {
+			t.Fatal(err)
 		}
 
-		querier, _ := s.Querier(context.Background(), test.mint, test.maxt)
-		actualQueriersCount := reflect.ValueOf(querier).Interface().(*mockMergeQuerier).queriersCount
-
-		if !reflect.DeepEqual(actualQueriersCount, test.expectedQueriersCount) {
-			t.Fatalf("%d. unexpected queriers count; want %v, got %v", i, test.expectedQueriersCount, actualQueriersCount)
+		if test.querier != q {
+			t.Errorf("%d. expected quierer %+v, got %+v", i, test.querier, q)
 		}
 	}
 }