Add connections by client

Signed-off-by: Felix Yuan <felix.yuan@reddit.com>

Author: Sticksman

collector/pg_connections_by_client.go

@@ -0,0 +1,100 @@
+// Copyright 2024 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package collector
+
+import (
+	"context"
+	"database/sql"
+	"log/slog"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const connectionsByClientSubsystem = "connections_by_client"
+
+func init() {
+	registerCollector(connectionsByClientSubsystem, defaultEnabled, NewPGConnectionsByClientCollector)
+}
+
+type PGConnectionByClientCollector struct {
+	log *slog.Logger
+}
+
+func NewPGConnectionsByClientCollector(config collectorConfig) (Collector, error) {
+	return &PGConnectionByClientCollector{
+		log: config.logger,
+	}, nil
+}
+
+var (
+	pgClientCountDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(
+			namespace,
+			connectionsByClientSubsystem,
+			"count",
+		),
+		"Number of clients",
+		[]string{"name"}, nil,
+	)
+
+	pgConnectionsByClientQuery = `
+	SELECT
+		count(*) as count,
+		client_hostname
+	FROM pg_stat_activity
+	WHERE client_hostname is not null
+	GROUP BY client_hostname;
+	`
+)
+
+func (c PGConnectionByClientCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+	db := instance.getDB()
+
+	rows, err := db.QueryContext(ctx,
+		pgConnectionsByClientQuery,
+	)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+	var clientCount sql.NullInt64
+	var clientName sql.NullString
+
+	for rows.Next() {
+		if err := rows.Scan(&clientCount, &clientName); err != nil {
+			return err
+		}
+
+		if !clientName.Valid {
+			continue
+		}
+
+		countMetric := 0.0
+		if clientCount.Valid {
+			countMetric = float64(clientCount.Int64)
+		}
+
+		ch <- prometheus.MustNewConstMetric(
+			pgClientCountDesc,
+			prometheus.GaugeValue,
+			countMetric,
+			clientName.String,
+		)
+	}
+	if err := rows.Err(); err != nil {
+		return err
+	}
+
+	return nil
+}

collector/pg_connections_by_client_test.go

@@ -0,0 +1,48 @@
+package collector
+
+import (
+	"context"
+	"testing"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/smartystreets/goconvey/convey"
+)
+
+func TestPGConnectionsByClientCollector(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub db connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &instance{db: db}
+
+	rows := sqlmock.NewRows([]string{"count", "client_name"}).
+		AddRow(42, "test")
+
+	mock.ExpectQuery(sanitizeQuery(pgConnectionsByClientQuery)).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGConnectionByClientCollector{}
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGConnectionsByClientCollector.Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{"name": "test"}, value: 42, metricType: dto.MetricType_GAUGE},
+	}
+	convey.Convey("Metrics comparison", t, func() {
+		for _, expect := range expected {
+			m := readMetric(<-ch)
+			convey.So(expect, convey.ShouldResemble, m)
+		}
+	})
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("there were unfulfilled exceptions: %s", err)
+	}
+}