Scraping: add metric for symbol table size

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

scrape/metrics.go

@@ -34,6 +34,7 @@ type scrapeMetrics struct {
 	targetScrapePoolExceededTargetLimit prometheus.Counter
 	targetScrapePoolTargetLimit         *prometheus.GaugeVec
 	targetScrapePoolTargetsAdded        *prometheus.GaugeVec
+	targetScrapePoolSymbolTableItems    *prometheus.GaugeVec
 	targetSyncIntervalLength            *prometheus.SummaryVec
 	targetSyncFailed                    *prometheus.CounterVec
 
@@ -129,6 +130,13 @@ func newScrapeMetrics(reg prometheus.Registerer) (*scrapeMetrics, error) {
 		},
 		[]string{"scrape_job"},
 	)
+	sm.targetScrapePoolSymbolTableItems = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "prometheus_target_scrape_pool_symboltable_items",
+			Help: "Current number of symbols in table for this scrape pool.",
+		},
+		[]string{"scrape_job"},
+	)
 	sm.targetScrapePoolSyncsCounter = prometheus.NewCounterVec(
 		prometheus.CounterOpts{
 			Name: "prometheus_target_scrape_pool_sync_total",
@@ -234,6 +242,7 @@ func newScrapeMetrics(reg prometheus.Registerer) (*scrapeMetrics, error) {
 		sm.targetScrapePoolExceededTargetLimit,
 		sm.targetScrapePoolTargetLimit,
 		sm.targetScrapePoolTargetsAdded,
+		sm.targetScrapePoolSymbolTableItems,
 		sm.targetSyncFailed,
 		// Used by targetScraper.
 		sm.targetScrapeExceededBodySizeLimit,
@@ -274,6 +283,7 @@ func (sm *scrapeMetrics) Unregister() {
 	sm.reg.Unregister(sm.targetScrapePoolExceededTargetLimit)
 	sm.reg.Unregister(sm.targetScrapePoolTargetLimit)
 	sm.reg.Unregister(sm.targetScrapePoolTargetsAdded)
+	sm.reg.Unregister(sm.targetScrapePoolSymbolTableItems)
 	sm.reg.Unregister(sm.targetSyncFailed)
 	sm.reg.Unregister(sm.targetScrapeExceededBodySizeLimit)
 	sm.reg.Unregister(sm.targetScrapeCacheFlushForced)

scrape/scrape.go

@@ -246,6 +246,7 @@ func (sp *scrapePool) stop() {
 		sp.metrics.targetScrapePoolSyncsCounter.DeleteLabelValues(sp.config.JobName)
 		sp.metrics.targetScrapePoolTargetLimit.DeleteLabelValues(sp.config.JobName)
 		sp.metrics.targetScrapePoolTargetsAdded.DeleteLabelValues(sp.config.JobName)
+		sp.metrics.targetScrapePoolSymbolTableItems.DeleteLabelValues(sp.config.JobName)
 		sp.metrics.targetSyncIntervalLength.DeleteLabelValues(sp.config.JobName)
 		sp.metrics.targetSyncFailed.DeleteLabelValues(sp.config.JobName)
 	}
@@ -408,6 +409,7 @@ func (sp *scrapePool) Sync(tgs []*targetgroup.Group) {
 			}
 		}
 	}
+	sp.metrics.targetScrapePoolSymbolTableItems.WithLabelValues(sp.config.JobName).Set(float64(sp.symbolTable.Len()))
 	sp.targetMtx.Unlock()
 	sp.sync(all)