Migrate pg_locks to collector package

Migrate the `pg_locks_count` query from `main` to the `collector`
package.

Signed-off-by: SuperQ <superq@gmail.com>

README.md

@@ -73,7 +73,10 @@ This will build the docker image as `prometheuscommunity/postgres_exporter:${bra
 
 
 * `[no-]collector.database`
-  Enable the database collector (default: enabled).
+  Enable the `database` collector (default: enabled).
+
+* `[no-]collector.locks`
+  Enable the `locks` collector (default: enabled).
 
 * `[no-]collector.postmaster`
    Enable the `postmaster` collector (default: enabled).

cmd/postgres_exporter/postgres_exporter.go

@@ -176,15 +176,6 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		true,
 		0,
 	},
-	"pg_locks": {
-		map[string]ColumnMapping{
-			"datname": {LABEL, "Name of this database", nil, nil},
-			"mode":    {LABEL, "Type of Lock", nil, nil},
-			"count":   {GAUGE, "Number of locks", nil, nil},
-		},
-		true,
-		0,
-	},
 	"pg_stat_replication": {
 		map[string]ColumnMapping{
 			"procpid":                  {DISCARD, "Process ID of a WAL sender process", nil, semver.MustParseRange("<9.2.0")},

cmd/postgres_exporter/queries.go

@@ -46,31 +46,6 @@ type OverrideQuery struct {
 // Overriding queries for namespaces above.
 // TODO: validate this is a closed set in tests, and there are no overlaps
 var queryOverrides = map[string][]OverrideQuery{
-	"pg_locks": {
-		{
-			semver.MustParseRange(">0.0.0"),
-			`SELECT pg_database.datname,tmp.mode,COALESCE(count,0) as count
-			FROM
-				(
-				  VALUES ('accesssharelock'),
-				         ('rowsharelock'),
-				         ('rowexclusivelock'),
-				         ('shareupdateexclusivelock'),
-				         ('sharelock'),
-				         ('sharerowexclusivelock'),
-				         ('exclusivelock'),
-				         ('accessexclusivelock'),
-					 ('sireadlock')
-				) AS tmp(mode) CROSS JOIN pg_database
-			LEFT JOIN
-			  (SELECT database, lower(mode) AS mode,count(*) AS count
-			  FROM pg_locks WHERE database IS NOT NULL
-			  GROUP BY database, lower(mode)
-			) AS tmp2
-			ON tmp.mode=tmp2.mode and pg_database.oid = tmp2.database ORDER BY 1`,
-		},
-	},
-
 	"pg_stat_replication": {
 		{
 			semver.MustParseRange(">=10.0.0"),

collector/pg_locks.go

@@ -0,0 +1,129 @@
+// 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/prometheus/client_golang/prometheus"
+)
+
+const locksSubsystem = "locks"
+
+func init() {
+	registerCollector(locksSubsystem, defaultEnabled, NewPGLocksCollector)
+}
+
+type PGLocksCollector struct {
+	log log.Logger
+}
+
+func NewPGLocksCollector(config collectorConfig) (Collector, error) {
+	return &PGLocksCollector{
+		log: config.logger,
+	}, nil
+}
+
+var (
+	pgLocksDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(
+			namespace,
+			locksSubsystem,
+			"count",
+		),
+		"Number of locks",
+		[]string{"datname", "mode"}, nil,
+	)
+
+	pgLocksQuery = `
+		SELECT 
+		  pg_database.datname as datname,
+		  tmp.mode as mode,
+		  COALESCE(count, 0) as count 
+		FROM 
+		  (
+		    VALUES 
+		      ('accesssharelock'), 
+		      ('rowsharelock'), 
+		      ('rowexclusivelock'), 
+		      ('shareupdateexclusivelock'), 
+		      ('sharelock'), 
+		      ('sharerowexclusivelock'), 
+		      ('exclusivelock'), 
+		      ('accessexclusivelock'), 
+		      ('sireadlock')
+		  ) AS tmp(mode)
+		  CROSS JOIN pg_database 
+		  LEFT JOIN (
+		    SELECT 
+		      database, 
+		      lower(mode) AS mode, 
+		      count(*) AS count 
+		    FROM 
+		      pg_locks 
+		    WHERE 
+		      database IS NOT NULL 
+		    GROUP BY 
+		      database, 
+		      lower(mode)
+		  ) AS tmp2 ON tmp.mode = tmp2.mode 
+		  and pg_database.oid = tmp2.database 
+		ORDER BY 
+		  1
+	`
+)
+
+// Update implements Collector and exposes database locks.
+// It is called by the Prometheus registry when collecting metrics.
+func (c PGLocksCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+	db := instance.getDB()
+	// Query the list of databases
+	rows, err := db.QueryContext(ctx,
+		pgLocksQuery,
+	)
+	if err != nil {
+		return err
+	}
+	defer rows.Close()
+
+	var datname, mode sql.NullString
+	var count sql.NullInt64
+
+	for rows.Next() {
+		if err := rows.Scan(&datname, &mode, &count); err != nil {
+			return err
+		}
+
+		if !datname.Valid || !mode.Valid {
+			continue
+		}
+
+		countMetric := 0.0
+		if count.Valid {
+			countMetric = float64(count.Int64)
+		}
+
+		ch <- prometheus.MustNewConstMetric(
+			pgLocksDesc,
+			prometheus.GaugeValue, countMetric,
+			datname.String, mode.String,
+		)
+	}
+	if err := rows.Err(); err != nil {
+		return err
+	}
+	return nil
+}

collector/pg_locks_test.go

@@ -0,0 +1,60 @@
+// 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 TestPGLocksCollector(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{"datname", "mode", "count"}).
+		AddRow("test", "exclusivelock", 42)
+
+	mock.ExpectQuery(sanitizeQuery(pgLocksQuery)).WillReturnRows(rows)
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := PGLocksCollector{}
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling PGLocksCollector.Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{"datname": "test", "mode": "exclusivelock"}, 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)
+	}
+}