Gitlab collector: Database wraparound collector and test (#834)

* Database wraparound collector and test

---------

Signed-off-by: Felix Yuan <felix.yuan@reddit.com>
Co-authored-by: Joe Adams <github@joeadams.io>

Author: Sticksman

collector/pg_database_wraparound.go

@@ -0,0 +1,115 @@
+// Copyright 2023 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"
+
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const databaseWraparoundSubsystem = "database_wraparound"
+
+func init() {
+	registerCollector(databaseWraparoundSubsystem, defaultDisabled, NewPGDatabaseWraparoundCollector)
+}
+
+type PGDatabaseWraparoundCollector struct {
+	log log.Logger
+}
+
+func NewPGDatabaseWraparoundCollector(config collectorConfig) (Collector, error) {
+	return &PGDatabaseWraparoundCollector{log: config.logger}, nil
+}
+
+var (
+	databaseWraparoundAgeDatfrozenxid = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, databaseWraparoundSubsystem, "age_datfrozenxid_seconds"),
+		"Age of the oldest transaction ID that has not been frozen.",
+		[]string{"datname"},
+		prometheus.Labels{},
+	)
+	databaseWraparoundAgeDatminmxid = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, databaseWraparoundSubsystem, "age_datminmxid_seconds"),
+		"Age of the oldest multi-transaction ID that has been replaced with a transaction ID.",
+		[]string{"datname"},
+		prometheus.Labels{},
+	)
+
+	databaseWraparoundQuery = `
+	SELECT
+		datname,
+		age(d.datfrozenxid) as age_datfrozenxid,
+		mxid_age(d.datminmxid) as age_datminmxid
+	FROM
+		pg_catalog.pg_database d
+	WHERE
+		d.datallowconn
+	`
+)
+
+func (c *PGDatabaseWraparoundCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+	db := instance.getDB()
+	rows, err := db.QueryContext(ctx,
+		databaseWraparoundQuery)
+
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var datname sql.NullString
+		var ageDatfrozenxid, ageDatminmxid sql.NullFloat64
+
+		if err := rows.Scan(&datname, &ageDatfrozenxid, &ageDatminmxid); err != nil {
+			return err
+		}
+
+		if !datname.Valid {
+			level.Debug(c.log).Log("msg", "Skipping database with NULL name")
+			continue
+		}
+		if !ageDatfrozenxid.Valid {
+			level.Debug(c.log).Log("msg", "Skipping stat emission with NULL age_datfrozenxid")
+			continue
+		}
+		if !ageDatminmxid.Valid {
+			level.Debug(c.log).Log("msg", "Skipping stat emission with NULL age_datminmxid")
+			continue
+		}
+
+		ageDatfrozenxidMetric := ageDatfrozenxid.Float64
+
+		ch <- prometheus.MustNewConstMetric(
+			databaseWraparoundAgeDatfrozenxid,
+			prometheus.GaugeValue,
+			ageDatfrozenxidMetric, datname.String,
+		)
+
+		ageDatminmxidMetric := ageDatminmxid.Float64
+		ch <- prometheus.MustNewConstMetric(
+			databaseWraparoundAgeDatminmxid,
+			prometheus.GaugeValue,
+			ageDatminmxidMetric, datname.String,
+		)
+	}
+	if err := rows.Err(); err != nil {
+		return err
+	}
+	return nil
+}

collector/pg_database_wraparound_test.go

@@ -0,0 +1,64 @@
+// Copyright 2023 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"
+	"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 TestPGDatabaseWraparoundCollector(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}
+	columns := []string{
+		"datname",
+		"age_datfrozenxid",
+		"age_datminmxid",
+	}
+	rows := sqlmock.NewRows(columns).
+		AddRow("newreddit", 87126426, 0)
+
+	mock.ExpectQuery(sanitizeQuery(databaseWraparoundQuery)).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGDatabaseWraparoundCollector{}
+
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGDatabaseWraparoundCollector.Update: %s", err)
+		}
+	}()
+	expected := []MetricResult{
+		{labels: labelMap{"datname": "newreddit"}, value: 87126426, metricType: dto.MetricType_GAUGE},
+		{labels: labelMap{"datname": "newreddit"}, value: 0, 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)
+	}
+}