feat: Add safe_wal_size to replication_slot

Author: MarcWort

collector/pg_replication_slot.go

@@ -63,6 +63,15 @@ var (
 "whether the replication slot is active or not",
 []string{"slot_name", "slot_type"}, nil,
 )
+pgReplicationSlotSafeWal = prometheus.NewDesc(
+prometheus.BuildFQName(
+namespace,
+replicationSlotSubsystem,
+"safe_wal_size",
+),
+"number of bytes that can be written to WAL such that this slot is not in danger of getting in state lost",
+[]string{"slot_name", "slot_type"}, nil,
+)
 
 pgReplicationSlotQuery = `SELECT
 slot_name,
@@ -73,7 +82,8 @@ var (
  pg_current_wal_lsn() - '0/0'
 END AS current_wal_lsn,
 COALESCE(confirmed_flush_lsn, '0/0') - '0/0' AS confirmed_flush_lsn,
-active
+active,
+safe_wal_size
 FROM pg_replication_slots;`
 )
 
@@ -92,7 +102,8 @@ func (PGReplicationSlotCollector) Update(ctx context.Context, instance *instance
 var walLSN sql.NullFloat64
 var flushLSN sql.NullFloat64
 var isActive sql.NullBool
-if err := rows.Scan(&slotName, &slotType, &walLSN, &flushLSN, &isActive); err != nil {
+var safeWalSize sql.NullInt64
+if err := rows.Scan(&slotName, &slotType, &walLSN, &flushLSN, &isActive, &safeWalSize); err != nil {
 return err
 }
 
@@ -131,6 +142,13 @@ func (PGReplicationSlotCollector) Update(ctx context.Context, instance *instance
 pgReplicationSlotIsActiveDesc,
 prometheus.GaugeValue, isActiveValue, slotNameLabel, slotTypeLabel,
 )
+
+if safeWalSize.Valid {
+ch <- prometheus.MustNewConstMetric(
+pgReplicationSlotSafeWal,
+prometheus.GaugeValue, float64(safeWalSize.Int64), slotNameLabel, slotTypeLabel,
+)
+}
 }
 return rows.Err()
 }

collector/pg_replication_slot_test.go

@@ -31,9 +31,9 @@ func TestPgReplicationSlotCollectorActive(t *testing.T) {
 
 inst := &instance{db: db}
 
-columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active"}
+columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size"}
 rows := sqlmock.NewRows(columns).
-AddRow("test_slot", "physical", 5, 3, true)
+AddRow("test_slot", "physical", 5, 3, true, 323906992)
 mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
 
 ch := make(chan prometheus.Metric)
@@ -50,6 +50,7 @@ func TestPgReplicationSlotCollectorActive(t *testing.T) {
 {labels: labelMap{"slot_name": "test_slot", "slot_type": "physical"}, value: 5, metricType: dto.MetricType_GAUGE},
 {labels: labelMap{"slot_name": "test_slot", "slot_type": "physical"}, value: 3, metricType: dto.MetricType_GAUGE},
 {labels: labelMap{"slot_name": "test_slot", "slot_type": "physical"}, value: 1, metricType: dto.MetricType_GAUGE},
+{labels: labelMap{"slot_name": "test_slot", "slot_type": "physical"}, value: 323906992, metricType: dto.MetricType_GAUGE},
 }
 
 convey.Convey("Metrics comparison", t, func() {
@@ -72,9 +73,9 @@ func TestPgReplicationSlotCollectorInActive(t *testing.T) {
 
 inst := &instance{db: db}
 
-columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active"}
+columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size"}
 rows := sqlmock.NewRows(columns).
-AddRow("test_slot", "physical", 6, 12, false)
+AddRow("test_slot", "physical", 6, 12, false, -4000)
 mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
 
 ch := make(chan prometheus.Metric)
@@ -90,6 +91,7 @@ func TestPgReplicationSlotCollectorInActive(t *testing.T) {
 expected := []MetricResult{
 {labels: labelMap{"slot_name": "test_slot", "slot_type": "physical"}, value: 6, metricType: dto.MetricType_GAUGE},
 {labels: labelMap{"slot_name": "test_slot", "slot_type": "physical"}, value: 0, metricType: dto.MetricType_GAUGE},
+{labels: labelMap{"slot_name": "test_slot", "slot_type": "physical"}, value: -4000, metricType: dto.MetricType_GAUGE},
 }
 
 convey.Convey("Metrics comparison", t, func() {
@@ -113,9 +115,9 @@ func TestPgReplicationSlotCollectorActiveNil(t *testing.T) {
 
 inst := &instance{db: db}
 
-columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active"}
+columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size"}
 rows := sqlmock.NewRows(columns).
-AddRow("test_slot", "physical", 6, 12, nil)
+AddRow("test_slot", "physical", 6, 12, nil, nil)
 mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
 
 ch := make(chan prometheus.Metric)
@@ -153,9 +155,9 @@ func TestPgReplicationSlotCollectorTestNilValues(t *testing.T) {
 
 inst := &instance{db: db}
 
-columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active"}
+columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size"}
 rows := sqlmock.NewRows(columns).
-AddRow(nil, nil, nil, nil, true)
+AddRow(nil, nil, nil, nil, true, nil)
 mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
 
 ch := make(chan prometheus.Metric)