fix: handle pg_replication_slots on pg<13 (#1098)

* fix: handle pg_replication_slots on pg<13

Signed-off-by: Michael Todorovic <michael.todorovic@outlook.com>

* fix: tests

Signed-off-by: Michael Todorovic <michael.todorovic@outlook.com>

---------

Signed-off-by: Michael Todorovic <michael.todorovic@outlook.com>

collector/pg_replication_slot.go

@@ -18,6 +18,7 @@ import (
 	"database/sql"
 	"log/slog"
 
+	"github.com/blang/semver/v4"
 	"github.com/prometheus/client_golang/prometheus"
 )
 
@@ -81,8 +82,18 @@ var (
 		"availability of WAL files claimed by this slot",
 		[]string{"slot_name", "slot_type", "wal_status"}, nil,
 	)
-
 	pgReplicationSlotQuery = `SELECT
+		slot_name,
+		slot_type,
+		CASE WHEN pg_is_in_recovery() THEN
+		    pg_last_wal_receive_lsn() - '0/0'
+		ELSE
+		    pg_current_wal_lsn() - '0/0'
+		END AS current_wal_lsn,
+		COALESCE(confirmed_flush_lsn, '0/0') - '0/0' AS confirmed_flush_lsn,
+		active
+	FROM pg_replication_slots;`
+	pgReplicationSlotNewQuery = `SELECT
 		slot_name,
 		slot_type,
 		CASE WHEN pg_is_in_recovery() THEN
@@ -98,9 +109,15 @@ var (
 )
 
 func (PGReplicationSlotCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+	query := pgReplicationSlotQuery
+	abovePG13 := instance.version.GTE(semver.MustParse("13.0.0"))
+	if abovePG13 {
+		query = pgReplicationSlotNewQuery
+	}
+
 	db := instance.getDB()
 	rows, err := db.QueryContext(ctx,
-		pgReplicationSlotQuery)
+		query)
 	if err != nil {
 		return err
 	}
@@ -114,7 +131,22 @@ func (PGReplicationSlotCollector) Update(ctx context.Context, instance *instance
 		var isActive sql.NullBool
 		var safeWalSize sql.NullInt64
 		var walStatus sql.NullString
-		if err := rows.Scan(&slotName, &slotType, &walLSN, &flushLSN, &isActive, &safeWalSize, &walStatus); err != nil {
+
+		r := []any{
+			&slotName,
+			&slotType,
+			&walLSN,
+			&flushLSN,
+			&isActive,
+		}
+
+		if abovePG13 {
+			r = append(r, &safeWalSize)
+			r = append(r, &walStatus)
+		}
+
+		err := rows.Scan(r...)
+		if err != nil {
 			return err
 		}
 

collector/pg_replication_slot_test.go

@@ -17,6 +17,7 @@ import (
 	"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/smartystreets/goconvey/convey"
@@ -29,12 +30,12 @@ func TestPgReplicationSlotCollectorActive(t *testing.T) {
 	}
 	defer db.Close()
 
-	inst := &instance{db: db}
+	inst := &instance{db: db, version: semver.MustParse("13.3.7")}
 
 	columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size", "wal_status"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("test_slot", "physical", 5, 3, true, 323906992, "reserved")
-	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotNewQuery)).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -72,12 +73,12 @@ func TestPgReplicationSlotCollectorInActive(t *testing.T) {
 	}
 	defer db.Close()
 
-	inst := &instance{db: db}
+	inst := &instance{db: db, version: semver.MustParse("13.3.7")}
 
 	columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size", "wal_status"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("test_slot", "physical", 6, 12, false, -4000, "extended")
-	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotNewQuery)).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -115,12 +116,12 @@ func TestPgReplicationSlotCollectorActiveNil(t *testing.T) {
 	}
 	defer db.Close()
 
-	inst := &instance{db: db}
+	inst := &instance{db: db, version: semver.MustParse("13.3.7")}
 
 	columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size", "wal_status"}
 	rows := sqlmock.NewRows(columns).
 		AddRow("test_slot", "physical", 6, 12, nil, nil, "lost")
-	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotNewQuery)).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {
@@ -156,12 +157,12 @@ func TestPgReplicationSlotCollectorTestNilValues(t *testing.T) {
 	}
 	defer db.Close()
 
-	inst := &instance{db: db}
+	inst := &instance{db: db, version: semver.MustParse("13.3.7")}
 
 	columns := []string{"slot_name", "slot_type", "current_wal_lsn", "confirmed_flush_lsn", "active", "safe_wal_size", "wal_status"}
 	rows := sqlmock.NewRows(columns).
 		AddRow(nil, nil, nil, nil, true, nil, nil)
-	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotQuery)).WillReturnRows(rows)
+	mock.ExpectQuery(sanitizeQuery(pgReplicationSlotNewQuery)).WillReturnRows(rows)
 
 	ch := make(chan prometheus.Metric)
 	go func() {