lib/promscrape: follow-up for 97373b7786

Substitute O(N^2) algorithm for exposing the `vm_promscrape_scrape_pool_targets` metric
with O(N) algorithm, where N is the number of scrape jobs. The previous algorithm could slow down
/metrics exposition significantly when -promscrape.config contains thousands of scrape jobs.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5311
Updates https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5335

docs/CHANGELOG.md

@@ -37,7 +37,7 @@ The sandbox cluster installation is running under the constant load generated by
 * FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): show all the dropped targets together with the reason why they are dropped at `http://vmagent:8429/service-discovery` page. Previously targets, which were dropped because of [target sharding](https://docs.victoriametrics.com/vmagent.html#scraping-big-number-of-targets) weren't displayed on this page. This could complicate service discovery debugging. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5389).
 * FEATURE: reduce the default value for `-import.maxLineLen` command-line flag from 100MB to 10MB in order to prevent excessive memory usage during data import via [/api/v1/import](https://docs.victoriametrics.com/#how-to-import-data-in-json-line-format).
 * FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): add `keep_if_contains` and `drop_if_contains` relabeling actions. See [these docs](https://docs.victoriametrics.com/vmagent.html#relabeling-enhancements) for details.
-* FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): export `vm_promscrape_scrape_pool_targets` metric to track the number of targets that each scrape_job discovers. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5311).
+* FEATURE: [vmagent](https://docs.victoriametrics.com/vmagent.html): export `vm_promscrape_scrape_pool_targets` [metric](https://docs.victoriametrics.com/vmagent.html#monitoring) to track the number of targets each scrape job discovers. See [this feature request](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5311).
 * FEATURE: [vmalert](https://docs.victoriametrics.com/vmalert.html): provide `/vmalert/api/v1/rule` and `/api/v1/rule` API endpoints to get the rule object in JSON format. See [these docs](https://docs.victoriametrics.com/vmalert.html#web) for details.
 * FEATURE: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): add [day_of_year()](https://docs.victoriametrics.com/MetricsQL.html#day_of_year) function, which returns the day of the year for each of the given unix timestamps. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5345) for details. Thanks to @luckyxiaoqiang for the [pull request](https://github.com/VictoriaMetrics/VictoriaMetrics/pull/5368/).
 * FEATURE: all VictoriaMetrics binaries: expose additional metrics at `/metrics` page, which may simplify debugging of VictoriaMetrics components (see [this feature request](https://github.com/VictoriaMetrics/metrics/issues/54)):

lib/promscrape/scrapework_test.go

@@ -104,9 +104,11 @@ func TestScrapeWorkScrapeInternalFailure(t *testing.T) {
 	}
 
 	timestamp := int64(123000)
+	tsmGlobal.Register(&sw)
 	if err := sw.scrapeInternal(timestamp, timestamp); err == nil {
 		t.Fatalf("expecting non-nil error")
 	}
+	tsmGlobal.Unregister(&sw)
 	if pushDataErr != nil {
 		t.Fatalf("unexpected error: %s", pushDataErr)
 	}
@@ -152,11 +154,13 @@ func TestScrapeWorkScrapeInternalSuccess(t *testing.T) {
 		}
 
 		timestamp := int64(123000)
+		tsmGlobal.Register(&sw)
 		if err := sw.scrapeInternal(timestamp, timestamp); err != nil {
 			if !strings.Contains(err.Error(), "sample_limit") {
 				t.Fatalf("unexpected error: %s", err)
 			}
 		}
+		tsmGlobal.Unregister(&sw)
 		if pushDataErr != nil {
 			t.Fatalf("unexpected error: %s", pushDataErr)
 		}

lib/promscrape/targetstatus.go

@@ -13,6 +13,7 @@ import (
 	"time"
 	"unsafe"
 
+	"github.com/VictoriaMetrics/VictoriaMetrics/lib/logger"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promrelabel"
 	"github.com/VictoriaMetrics/VictoriaMetrics/lib/promutils"
 	"github.com/VictoriaMetrics/metrics"
@@ -88,91 +89,108 @@ type targetStatusMap struct {
 	mu       sync.Mutex
 	m        map[*scrapeWork]*targetStatus
 	jobNames []string
+
+	// the current number of `up` targets in the given jobName
+	upByJob map[string]int
+
+	// the current number of `down` targets in the given jobName
+	downByJob map[string]int
 }
 
 func newTargetStatusMap() *targetStatusMap {
 	return &targetStatusMap{
-		m: make(map[*scrapeWork]*targetStatus),
+		m:         make(map[*scrapeWork]*targetStatus),
+		upByJob:   make(map[string]int),
+		downByJob: make(map[string]int),
 	}
 }
 
-func (tsm *targetStatusMap) Reset() {
-	tsm.mu.Lock()
-	tsm.m = make(map[*scrapeWork]*targetStatus)
-	tsm.mu.Unlock()
-}
-
 func (tsm *targetStatusMap) registerJobNames(jobNames []string) {
 	tsm.mu.Lock()
-	tsm.registerJobsMetrics(tsm.jobNames, jobNames)
+	tsm.registerJobsMetricsLocked(tsm.jobNames, jobNames)
 	tsm.jobNames = append(tsm.jobNames[:0], jobNames...)
 	tsm.mu.Unlock()
 }
 
-// registerJobsMetrics registers metrics for new jobs and unregisterMetric metrics for removed jobs
+// registerJobsMetricsLocked registers metrics for new jobs and unregisters metrics for removed jobs
-func (tsm *targetStatusMap) registerJobsMetrics(prevJobNames, currentJobNames []string) {
+//
-	prevName := make(map[string]struct{}, len(prevJobNames))
+// tsm.mu must be locked when calling this function.
-	currentName := make(map[string]struct{}, len(currentJobNames))
+func (tsm *targetStatusMap) registerJobsMetricsLocked(prevJobNames, currentJobNames []string) {
-	for _, n := range currentJobNames {
+	prevNames := make(map[string]struct{}, len(prevJobNames))
-		currentName[n] = struct{}{}
+	currentNames := make(map[string]struct{}, len(currentJobNames))
+	for _, jobName := range currentJobNames {
+		currentNames[jobName] = struct{}{}
 	}
-	for _, n := range prevJobNames {
+	for _, jobName := range prevJobNames {
-		prevName[n] = struct{}{}
+		prevNames[jobName] = struct{}{}
-		if _, ok := currentName[n]; !ok {
+		if _, ok := currentNames[jobName]; !ok {
-			metrics.UnregisterMetric(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="up"}`, n))
+			metrics.UnregisterMetric(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="up"}`, jobName))
-			metrics.UnregisterMetric(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="down"}`, n))
+			metrics.UnregisterMetric(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="down"}`, jobName))
 		}
 	}
 
-	for _, n := range currentJobNames {
+	for _, jobName := range currentJobNames {
-		if _, ok := prevName[n]; !ok {
+		if _, ok := prevNames[jobName]; ok {
-			n := n
+			continue
-			_ = metrics.NewGauge(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="up"}`, n), func() float64 {
-				jobStatus := tsm.getTargetsStatusByJob(&requestFilter{
-					originalJobName: n,
-				})
-				var up float64
-				for _, status := range jobStatus.jobTargetsStatuses {
-					up = +float64(status.upCount)
-				}
-				return up
-			})
-			_ = metrics.NewGauge(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="down"}`, n), func() float64 {
-				jobStatus := tsm.getTargetsStatusByJob(&requestFilter{
-					originalJobName: n,
-				})
-				var down float64
-				for _, status := range jobStatus.jobTargetsStatuses {
-					down = +float64(status.targetsTotal - status.upCount)
-				}
-				return down
-			})
 		}
+		jobNameLocal := jobName
+		_ = metrics.NewGauge(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="up"}`, jobName), func() float64 {
+			tsm.mu.Lock()
+			n := tsm.upByJob[jobNameLocal]
+			tsm.mu.Unlock()
+			return float64(n)
+		})
+		_ = metrics.NewGauge(fmt.Sprintf(`vm_promscrape_scrape_pool_targets{scrape_job=%q, status="down"}`, jobName), func() float64 {
+			tsm.mu.Lock()
+			n := tsm.downByJob[jobNameLocal]
+			tsm.mu.Unlock()
+			return float64(n)
+		})
 	}
 }
 
 func (tsm *targetStatusMap) Register(sw *scrapeWork) {
+	jobName := sw.Config.jobNameOriginal
+
 	tsm.mu.Lock()
 	tsm.m[sw] = &targetStatus{
 		sw: sw,
 	}
+	tsm.downByJob[jobName]++
 	tsm.mu.Unlock()
 }
 
 func (tsm *targetStatusMap) Unregister(sw *scrapeWork) {
+	jobName := sw.Config.jobNameOriginal
+
 	tsm.mu.Lock()
+	ts, ok := tsm.m[sw]
+	if !ok {
+		logger.Panicf("BUG: missing Register() call for the target %q", jobName)
+	}
+	if ts.up {
+		tsm.upByJob[jobName]--
+	} else {
+		tsm.downByJob[jobName]--
+	}
 	delete(tsm.m, sw)
 	tsm.mu.Unlock()
 }
 
 func (tsm *targetStatusMap) Update(sw *scrapeWork, up bool, scrapeTime, scrapeDuration int64, samplesScraped int, err error) {
+	jobName := sw.Config.jobNameOriginal
+
 	tsm.mu.Lock()
-	ts := tsm.m[sw]
+	ts, ok := tsm.m[sw]
-	if ts == nil {
+	if !ok {
-		ts = &targetStatus{
+		logger.Panicf("BUG: missing Register() call for the target %q", jobName)
-			sw: sw,
+	}
-		}
+	if up && !ts.up {
-		tsm.m[sw] = ts
+		tsm.upByJob[jobName]++
+		tsm.downByJob[jobName]--
+	} else if !up && ts.up {
+		tsm.upByJob[jobName]--
+		tsm.downByJob[jobName]++
 	}
 	ts.up = up
 	ts.scrapeTime = scrapeTime