Add the instance struct to handle connections

The intent is to use the instance struct to hold the connection to the database as well as metadata about the instance. Currently this metadata only includes the version of postgres for the instance which can be used in the collectors to decide what query to run. In the future this could hold more metadata but for now it keeps the Collector interface arguments to a reasonable number. Signed-off-by: Joe Adams <github@joeadams.io>

Author: sysadmind

collector/collector.go

@@ -15,7 +15,6 @@ package collector
 
 import (
 "context"
-"database/sql"
 "errors"
 "fmt"
 "sync"
@@ -59,7 +58,7 @@ var (
 )
 
 type Collector interface {
-Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error
+Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error
 }
 
 type collectorConfig struct {
@@ -92,7 +91,7 @@ type PostgresCollector struct {
 Collectors map[string]Collector
 logger log.Logger
 
-db *sql.DB
+instance *instance
 }
 
 type Option func(*PostgresCollector) error
@@ -149,14 +148,11 @@ func NewPostgresCollector(logger log.Logger, excludeDatabases []string, dsn stri
 return nil, errors.New("empty dsn")
 }
 
-db, err := sql.Open("postgres", dsn)
+instance, err := newInstance(dsn)
 if err != nil {
 return nil, err
 }
-db.SetMaxOpenConns(1)
-db.SetMaxIdleConns(1)
-
-p.db = db
+p.instance = instance
 
 return p, nil
 }
@@ -174,16 +170,16 @@ func (p PostgresCollector) Collect(ch chan<- prometheus.Metric) {
 wg.Add(len(p.Collectors))
 for name, c := range p.Collectors {
 go func(name string, c Collector) {
-execute(ctx, name, c, p.db, ch, p.logger)
+execute(ctx, name, c, p.instance, ch, p.logger)
 wg.Done()
 }(name, c)
 }
 wg.Wait()
 }
 
-func execute(ctx context.Context, name string, c Collector, db *sql.DB, ch chan<- prometheus.Metric, logger log.Logger) {
+func execute(ctx context.Context, name string, c Collector, instance *instance, ch chan<- prometheus.Metric, logger log.Logger) {
 begin := time.Now()
-err := c.Update(ctx, db, ch)
+err := c.Update(ctx, instance, ch)
 duration := time.Since(begin)
 var success float64
 

collector/instance.go

@@ -0,0 +1,85 @@
+// 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 (
+"database/sql"
+"fmt"
+"regexp"
+
+"github.com/blang/semver/v4"
+)
+
+type instance struct {
+db *sql.DB
+version semver.Version
+}
+
+func newInstance(dsn string) (*instance, error) {
+i := &instance{}
+db, err := sql.Open("postgres", dsn)
+if err != nil {
+return nil, err
+}
+db.SetMaxOpenConns(1)
+db.SetMaxIdleConns(1)
+i.db = db
+
+version, err := queryVersion(db)
+if err != nil {
+db.Close()
+return nil, err
+}
+
+i.version = version
+
+return i, nil
+}
+
+func (i *instance) getDB() *sql.DB {
+return i.db
+}
+
+func (i *instance) Close() error {
+return i.db.Close()
+}
+
+// Regex used to get the "short-version" from the postgres version field.
+// The result of SELECT version() is something like "PostgreSQL 9.6.2 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 6.2.1 20160830, 64-bit"
+var versionRegex = regexp.MustCompile(`^\w+ ((\d+)(\.\d+)?(\.\d+)?)`)
+var serverVersionRegex = regexp.MustCompile(`^((\d+)(\.\d+)?(\.\d+)?)`)
+
+func queryVersion(db *sql.DB) (semver.Version, error) {
+var version string
+err := db.QueryRow("SELECT version();").Scan(&version)
+if err != nil {
+return semver.Version{}, err
+}
+submatches := versionRegex.FindStringSubmatch(version)
+if len(submatches) > 1 {
+return semver.ParseTolerant(submatches[1])
+}
+
+// We could also try to parse the version from the server_version field.
+// This is of the format 13.3 (Debian 13.3-1.pgdg100+1)
+err = db.QueryRow("SHOW server_version;").Scan(&version)
+if err != nil {
+return semver.Version{}, err
+}
+submatches = serverVersionRegex.FindStringSubmatch(version)
+if len(submatches) > 1 {
+return semver.ParseTolerant(submatches[1])
+}
+return semver.Version{}, fmt.Errorf("could not parse version from %q", version)
+}

collector/pg_database.go

@@ -15,7 +15,6 @@ package collector
 
 import (
 "context"
-"database/sql"
 
 "github.com/go-kit/log"
 "github.com/prometheus/client_golang/prometheus"
@@ -66,7 +65,8 @@ var (
 // each database individually. This is because we can't filter the
 // list of databases in the query because the list of excluded
 // databases is dynamic.
-func (c PGDatabaseCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
+func (c PGDatabaseCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+db := instance.getDB()
 // Query the list of databases
 rows, err := db.QueryContext(ctx,
 pgDatabaseQuery,

collector/pg_database_test.go

@@ -29,6 +29,8 @@ func TestPGDatabaseCollector(t *testing.T) {
 }
 defer db.Close()
 
+inst := &instance{db: db}
+
 mock.ExpectQuery(sanitizeQuery(pgDatabaseQuery)).WillReturnRows(sqlmock.NewRows([]string{"datname"}).
 AddRow("postgres"))
 
@@ -39,7 +41,7 @@ func TestPGDatabaseCollector(t *testing.T) {
 go func() {
 defer close(ch)
 c := PGDatabaseCollector{}
-if err := c.Update(context.Background(), db, ch); err != nil {
+if err := c.Update(context.Background(), inst, ch); err != nil {
 t.Errorf("Error calling PGDatabaseCollector.Update: %s", err)
 }
 }()

collector/pg_postmaster.go

@@ -15,7 +15,6 @@ package collector
 
 import (
 "context"
-"database/sql"
 
 "github.com/prometheus/client_golang/prometheus"
 )
@@ -47,7 +46,8 @@ var (
 pgPostmasterQuery = "SELECT pg_postmaster_start_time from pg_postmaster_start_time();"
 )
 
-func (c *PGPostmasterCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
+func (c *PGPostmasterCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+db := instance.getDB()
 row := db.QueryRowContext(ctx,
 pgPostmasterQuery)
 

collector/pg_postmaster_test.go

@@ -29,6 +29,8 @@ func TestPgPostmasterCollector(t *testing.T) {
 }
 defer db.Close()
 
+inst := &instance{db: db}
+
 mock.ExpectQuery(sanitizeQuery(pgPostmasterQuery)).WillReturnRows(sqlmock.NewRows([]string{"pg_postmaster_start_time"}).
 AddRow(1685739904))
 
@@ -37,7 +39,7 @@ func TestPgPostmasterCollector(t *testing.T) {
 defer close(ch)
 c := PGPostmasterCollector{}
 
-if err := c.Update(context.Background(), db, ch); err != nil {
+if err := c.Update(context.Background(), inst, ch); err != nil {
 t.Errorf("Error calling PGPostmasterCollector.Update: %s", err)
 }
 }()

collector/pg_process_idle.go

@@ -15,7 +15,6 @@ package collector
 
 import (
 "context"
-"database/sql"
 
 "github.com/go-kit/log"
 "github.com/prometheus/client_golang/prometheus"
@@ -42,7 +41,8 @@ var pgProcessIdleSeconds = prometheus.NewDesc(
 prometheus.Labels{},
 )
 
-func (PGProcessIdleCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
+func (PGProcessIdleCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+db := instance.getDB()
 row := db.QueryRowContext(ctx,
 `WITH
 metrics AS (

collector/pg_replication_slot.go

@@ -15,7 +15,6 @@ package collector
 
 import (
 "context"
-"database/sql"
 
 "github.com/go-kit/log"
 "github.com/prometheus/client_golang/prometheus"
@@ -73,7 +72,8 @@ var (
 pg_replication_slots;`
 )
 
-func (PGReplicationSlotCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
+func (PGReplicationSlotCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+db := instance.getDB()
 rows, err := db.QueryContext(ctx,
 pgReplicationSlotQuery)
 if err != nil {

collector/pg_replication_slot_test.go

@@ -29,6 +29,8 @@ func TestPgReplicationSlotCollectorActive(t *testing.T) {
 }
 defer db.Close()
 
+inst := &instance{db: db}
+
 columns := []string{"slot_name", "current_wal_lsn", "confirmed_flush_lsn", "active"}
 rows := sqlmock.NewRows(columns).
 AddRow("test_slot", 5, 3, true)
@@ -39,7 +41,7 @@ func TestPgReplicationSlotCollectorActive(t *testing.T) {
 defer close(ch)
 c := PGReplicationSlotCollector{}
 
-if err := c.Update(context.Background(), db, ch); err != nil {
+if err := c.Update(context.Background(), inst, ch); err != nil {
 t.Errorf("Error calling PGPostmasterCollector.Update: %s", err)
 }
 }()
@@ -68,6 +70,8 @@ func TestPgReplicationSlotCollectorInActive(t *testing.T) {
 }
 defer db.Close()
 
+inst := &instance{db: db}
+
 columns := []string{"slot_name", "current_wal_lsn", "confirmed_flush_lsn", "active"}
 rows := sqlmock.NewRows(columns).
 AddRow("test_slot", 6, 12, false)
@@ -78,7 +82,7 @@ func TestPgReplicationSlotCollectorInActive(t *testing.T) {
 defer close(ch)
 c := PGReplicationSlotCollector{}
 
-if err := c.Update(context.Background(), db, ch); err != nil {
+if err := c.Update(context.Background(), inst, ch); err != nil {
 t.Errorf("Error calling PGReplicationSlotCollector.Update: %s", err)
 }
 }()

collector/pg_stat_bgwriter.go

@@ -15,7 +15,6 @@ package collector
 
 import (
 "context"
-"database/sql"
 "time"
 
 "github.com/prometheus/client_golang/prometheus"
@@ -117,7 +116,8 @@ var (
 FROM pg_stat_bgwriter;`
 )
 
-func (PGStatBGWriterCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
+func (PGStatBGWriterCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+db := instance.getDB()
 row := db.QueryRowContext(ctx,
 statBGWriterQuery)