From 36d3b1e9fb242cdaabde4acb2d40879c24d7fd40 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Guillot?= <f@miniflux.net>
Date: Sat, 22 May 2021 20:27:13 -0700
Subject: [PATCH] Add database stats to Prometheus exporter

---
 metric/metric.go   | 72 ++++++++++++++++++++++++++++++++++++++++++++++
 storage/storage.go |  8 ++++--
 2 files changed, 78 insertions(+), 2 deletions(-)

diff --git a/metric/metric.go b/metric/metric.go
index 8e1c972e..924f44ac 100644
--- a/metric/metric.go
+++ b/metric/metric.go
@@ -78,6 +78,62 @@ var (
 		},
 		[]string{"status"},
 	)
+
+	dbOpenConnectionsGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "miniflux",
+			Name:      "db_open_connections",
+			Help:      "The number of established connections both in use and idle",
+		},
+	)
+
+	dbConnectionsInUseGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "miniflux",
+			Name:      "db_connections_in_use",
+			Help:      "The number of connections currently in use",
+		},
+	)
+
+	dbConnectionsIdleGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "miniflux",
+			Name:      "db_connections_idle",
+			Help:      "The number of idle connections",
+		},
+	)
+
+	dbConnectionsWaitCountGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "miniflux",
+			Name:      "db_connections_wait_count",
+			Help:      "The total number of connections waited for",
+		},
+	)
+
+	dbConnectionsMaxIdleClosedGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "miniflux",
+			Name:      "db_connections_max_idle_closed",
+			Help:      "The total number of connections closed due to SetMaxIdleConns",
+		},
+	)
+
+	dbConnectionsMaxIdleTimeClosedGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "miniflux",
+			Name:      "db_connections_max_idle_time_closed",
+			Help:      "The total number of connections closed due to SetConnMaxIdleTime",
+		},
+	)
+
+	dbConnectionsMaxLifetimeClosedGauge = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: "miniflux",
+			Name:      "db_connections_max_lifetime_closed",
+			Help:      "The total number of connections closed due to SetConnMaxLifetime",
+		},
+	)
 )
 
 // Collector represents a metric collector.
@@ -95,6 +151,13 @@ func NewCollector(store *storage.Storage, refreshInterval int) *Collector {
 	prometheus.MustRegister(feedsGauge)
 	prometheus.MustRegister(brokenFeedsGauge)
 	prometheus.MustRegister(entriesGauge)
+	prometheus.MustRegister(dbOpenConnectionsGauge)
+	prometheus.MustRegister(dbConnectionsInUseGauge)
+	prometheus.MustRegister(dbConnectionsIdleGauge)
+	prometheus.MustRegister(dbConnectionsWaitCountGauge)
+	prometheus.MustRegister(dbConnectionsMaxIdleClosedGauge)
+	prometheus.MustRegister(dbConnectionsMaxIdleTimeClosedGauge)
+	prometheus.MustRegister(dbConnectionsMaxLifetimeClosedGauge)
 
 	return &Collector{store, refreshInterval}
 }
@@ -116,5 +179,14 @@ func (c *Collector) GatherStorageMetrics() {
 		for status, count := range entriesCount {
 			entriesGauge.WithLabelValues(status).Set(float64(count))
 		}
+
+		dbStats := c.store.DBStats()
+		dbOpenConnectionsGauge.Set(float64(dbStats.OpenConnections))
+		dbConnectionsInUseGauge.Set(float64(dbStats.InUse))
+		dbConnectionsIdleGauge.Set(float64(dbStats.Idle))
+		dbConnectionsWaitCountGauge.Set(float64(dbStats.WaitCount))
+		dbConnectionsMaxIdleClosedGauge.Set(float64(dbStats.MaxIdleClosed))
+		dbConnectionsMaxIdleTimeClosedGauge.Set(float64(dbStats.MaxIdleTimeClosed))
+		dbConnectionsMaxLifetimeClosedGauge.Set(float64(dbStats.MaxLifetimeClosed))
 	}
 }
diff --git a/storage/storage.go b/storage/storage.go
index ef73e569..947011bb 100644
--- a/storage/storage.go
+++ b/storage/storage.go
@@ -31,6 +31,10 @@ func (s *Storage) DatabaseVersion() string {
 
 // Ping checks if the database connection works.
 func (s *Storage) Ping() error {
-	_, err := s.db.Exec(`SELECT true`)
-	return err
+	return s.db.Ping()
+}
+
+// DBStats returns database statistics.
+func (s *Storage) DBStats() sql.DBStats {
+	return s.db.Stats()
 }