promql: make active query tracker context-aware (#6701)

* promql: make query logger context-aware
* Remove gate
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

promql/engine.go

@@ -33,7 +33,6 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/common/model"
 
-	"github.com/prometheus/prometheus/pkg/gate"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/pkg/timestamp"
 	"github.com/prometheus/prometheus/pkg/value"
@@ -189,12 +188,6 @@ func (q *query) Exec(ctx context.Context) *Result {
 		span.SetTag(queryTag, q.stmt.String())
 	}
 
-	// Log query in active log.
-	if q.ng.activeQueryTracker != nil {
-		queryIndex := q.ng.activeQueryTracker.Insert(q.q)
-		defer q.ng.activeQueryTracker.Delete(queryIndex)
-	}
-
 	// Exec query.
 	res, warnings, err := q.ng.exec(ctx, q)
 
@@ -236,7 +229,6 @@ type Engine struct {
 	logger             log.Logger
 	metrics            *engineMetrics
 	timeout            time.Duration
-	gate               *gate.Gate
 	maxSamplesPerQuery int
 	activeQueryTracker *ActiveQueryTracker
 	queryLogger        QueryLogger
@@ -323,7 +315,6 @@ func NewEngine(opts EngineOpts) *Engine {
 	}
 
 	return &Engine{
-		gate:               gate.New(opts.MaxConcurrent),
 		timeout:            opts.Timeout,
 		logger:             opts.Logger,
 		metrics:            metrics,
@@ -466,12 +457,16 @@ func (ng *Engine) exec(ctx context.Context, q *query) (v Value, w storage.Warnin
 	defer execSpanTimer.Finish()
 
 	queueSpanTimer, _ := q.stats.GetSpanTimer(ctx, stats.ExecQueueTime, ng.metrics.queryQueueTime)
-
-	if err := ng.gate.Start(ctx); err != nil {
+	// Log query in active log. The active log guarantees that we don't run over
+	// MaxConcurrent queries.
+	if ng.activeQueryTracker != nil {
+		queryIndex, err := ng.activeQueryTracker.Insert(ctx, q.q)
+		if err != nil {
+			queueSpanTimer.Finish()
 			return nil, nil, contextErr(err, "query queue")
 		}
-	defer ng.gate.Done()
-
+		defer ng.activeQueryTracker.Delete(queryIndex)
+	}
 	queueSpanTimer.Finish()
 
 	// Cancel when execution is done or an error was raised.

promql/engine_test.go

@@ -16,6 +16,8 @@ package promql
 import (
 	"context"
 	"errors"
+	"io/ioutil"
+	"os"
 	"strings"
 	"testing"
 	"time"
@@ -28,12 +30,20 @@ import (
 )
 
 func TestQueryConcurrency(t *testing.T) {
+	maxConcurrency := 10
+
+	dir, err := ioutil.TempDir("", "test_concurrency")
+	testutil.Ok(t, err)
+	defer os.RemoveAll(dir)
+	queryTracker := NewActiveQueryTracker(dir, maxConcurrency, nil)
+
 	opts := EngineOpts{
 		Logger:             nil,
 		Reg:                nil,
-		MaxConcurrent: 10,
+		MaxConcurrent:      maxConcurrency,
 		MaxSamples:         10,
 		Timeout:            100 * time.Second,
+		ActiveQueryTracker: queryTracker,
 	}
 
 	engine := NewEngine(opts)

promql/query_logger.go

@@ -14,6 +14,7 @@
 package promql
 
 import (
+	"context"
 	"encoding/json"
 	"os"
 	"path/filepath"
@@ -174,13 +175,17 @@ func (tracker ActiveQueryTracker) Delete(insertIndex int) {
 	tracker.getNextIndex <- insertIndex
 }
 
-func (tracker ActiveQueryTracker) Insert(query string) int {
-	i, fileBytes := <-tracker.getNextIndex, tracker.mmapedFile
+func (tracker ActiveQueryTracker) Insert(ctx context.Context, query string) (int, error) {
+	select {
+	case i := <-tracker.getNextIndex:
+		fileBytes := tracker.mmapedFile
 		entry := newJSONEntry(query, tracker.logger)
 		start, end := i, i+entrySize
 
 		copy(fileBytes[start:], entry)
 		copy(fileBytes[end-1:], ",")
-
-	return i
+		return i, nil
+	case <-ctx.Done():
+		return 0, ctx.Err()
+	}
 }

promql/query_logger_test.go

@@ -14,6 +14,7 @@
 package promql
 
 import (
+	"context"
 	"io/ioutil"
 	"os"
 	"regexp"
@@ -51,7 +52,7 @@ func TestQueryLogging(t *testing.T) {
 		start := 1 + i*entrySize
 		end := start + entrySize
 
-		queryLogger.Insert(queries[i])
+		queryLogger.Insert(context.Background(), queries[i])
 
 		have := string(fileAsBytes[start:end])
 		if !regexp.MustCompile(want[i]).MatchString(have) {
@@ -77,16 +78,16 @@ func TestIndexReuse(t *testing.T) {
 	}
 
 	queryLogger.generateIndices(3)
-	queryLogger.Insert("TestQuery1")
-	queryLogger.Insert("TestQuery2")
-	queryLogger.Insert("TestQuery3")
+	queryLogger.Insert(context.Background(), "TestQuery1")
+	queryLogger.Insert(context.Background(), "TestQuery2")
+	queryLogger.Insert(context.Background(), "TestQuery3")
 
 	queryLogger.Delete(1 + entrySize)
 	queryLogger.Delete(1)
 	newQuery2 := "ThisShouldBeInsertedAtIndex2"
 	newQuery1 := "ThisShouldBeInsertedAtIndex1"
-	queryLogger.Insert(newQuery2)
-	queryLogger.Insert(newQuery1)
+	queryLogger.Insert(context.Background(), newQuery2)
+	queryLogger.Insert(context.Background(), newQuery1)
 
 	want := []string{
 		`^{"query":"ThisShouldBeInsertedAtIndex1","timestamp_sec":\d+}\x00*,$`,