Add pg_synchronized_standby_slots_invalid metric

collector/pg_synchronized_standby_slots.go

@@ -0,0 +1,87 @@
+// Copyright 2025 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/blang/semver/v4"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+const synchronizedStandbySlotsSubsystem = "synchronized_standby_slots"
+
+func init() {
+	registerCollector(synchronizedStandbySlotsSubsystem, defaultEnabled, NewPGSynchronizedStandbySlotsCollector)
+}
+
+type PGSynchronizedStandbySlotsCollector struct {
+	log *slog.Logger
+}
+
+func NewPGSynchronizedStandbySlotsCollector(config collectorConfig) (Collector, error) {
+	return &PGSynchronizedStandbySlotsCollector{log: config.logger}, nil
+}
+
+var (
+	synchronizedStandbySlotsInvalidDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, synchronizedStandbySlotsSubsystem, "invalid"),
+		"Number of slots listed in synchronized_standby_slots that do not exist as physical replication slots. Non-zero means logical replication is blocked.",
+		[]string{},
+		nil,
+	)
+
+	synchronizedStandbySlotsQuery = `
+SELECT count(*) AS invalid_count
+FROM unnest(string_to_array(
+  (SELECT setting FROM pg_settings WHERE name = 'synchronized_standby_slots'),
+  ','
+)) AS configured(slot_name)
+WHERE trim(configured.slot_name) != ''
+  AND NOT EXISTS(
+    SELECT 1 FROM pg_replication_slots s
+    WHERE s.slot_name = trim(configured.slot_name)
+      AND s.slot_type = 'physical'
+  )
+`
+)
+
+func (c *PGSynchronizedStandbySlotsCollector) Update(ctx context.Context, instance *Instance, ch chan<- prometheus.Metric) error {
+	if instance.version.LT(semver.MustParse("17.0.0")) {
+		c.log.Debug("synchronized_standby_slots collector is not available on PostgreSQL < 17, skipping")
+		return nil
+	}
+
+	db := instance.getDB()
+
+	var invalidCount sql.NullInt64
+	if err := db.QueryRowContext(ctx, synchronizedStandbySlotsQuery).Scan(&invalidCount); err != nil {
+		return err
+	}
+
+	value := 0.0
+	if invalidCount.Valid {
+		value = float64(invalidCount.Int64)
+	}
+
+	ch <- prometheus.MustNewConstMetric(
+		synchronizedStandbySlotsInvalidDesc,
+		prometheus.GaugeValue,
+		value,
+	)
+
+	return nil
+}

collector/pg_synchronized_standby_slots_test.go

@@ -0,0 +1,162 @@
+// Copyright 2025 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/blang/semver/v4"
+	"github.com/prometheus/client_golang/prometheus"
+	dto "github.com/prometheus/client_model/go"
+	"github.com/prometheus/common/promslog"
+	"github.com/smartystreets/goconvey/convey"
+)
+
+func newTestSyncStandbySlotsCollector() *PGSynchronizedStandbySlotsCollector {
+	return &PGSynchronizedStandbySlotsCollector{log: promslog.NewNopLogger()}
+}
+
+func TestPGSynchronizedStandbySlotsBeforePG17(t *testing.T) {
+	db, _, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub database connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &Instance{db: db, version: semver.MustParse("16.4.0")}
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := newTestSyncStandbySlotsCollector()
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling Update: %s", err)
+		}
+	}()
+
+	// No metrics should be emitted for PG < 17
+	for range ch {
+		t.Error("Expected no metrics for PG < 17, but got one")
+	}
+}
+
+func TestPGSynchronizedStandbySlotsAllValid(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub database connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &Instance{db: db, version: semver.MustParse("17.0.0")}
+
+	mock.ExpectQuery(sanitizeQuery(synchronizedStandbySlotsQuery)).
+		WillReturnRows(sqlmock.NewRows([]string{"invalid_count"}).AddRow(0))
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := newTestSyncStandbySlotsCollector()
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{}, value: 0, metricType: dto.MetricType_GAUGE},
+	}
+
+	convey.Convey("All slots valid", 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 expectations: %s", err)
+	}
+}
+
+func TestPGSynchronizedStandbySlotsSomeInvalid(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub database connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &Instance{db: db, version: semver.MustParse("17.0.0")}
+
+	mock.ExpectQuery(sanitizeQuery(synchronizedStandbySlotsQuery)).
+		WillReturnRows(sqlmock.NewRows([]string{"invalid_count"}).AddRow(2))
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := newTestSyncStandbySlotsCollector()
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{}, value: 2, metricType: dto.MetricType_GAUGE},
+	}
+
+	convey.Convey("Some slots invalid", 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 expectations: %s", err)
+	}
+}
+
+func TestPGSynchronizedStandbySlotsEmptyGUC(t *testing.T) {
+	db, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("Error opening a stub database connection: %s", err)
+	}
+	defer db.Close()
+
+	inst := &Instance{db: db, version: semver.MustParse("17.0.0")}
+
+	mock.ExpectQuery(sanitizeQuery(synchronizedStandbySlotsQuery)).
+		WillReturnRows(sqlmock.NewRows([]string{"invalid_count"}).AddRow(0))
+
+	ch := make(chan prometheus.Metric)
+	go func() {
+		defer close(ch)
+		c := newTestSyncStandbySlotsCollector()
+		if err := c.Update(context.Background(), inst, ch); err != nil {
+			t.Errorf("Error calling Update: %s", err)
+		}
+	}()
+
+	expected := []MetricResult{
+		{labels: labelMap{}, value: 0, metricType: dto.MetricType_GAUGE},
+	}
+
+	convey.Convey("Empty GUC emits 0", 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 expectations: %s", err)
+	}
+}