fix postgresql connection leak (#2611)

plugins/inputs/postgresql_extensible/postgresql_extensible.go

@@ -2,11 +2,15 @@ package postgresql_extensible
 
 import (
 	"bytes"
+	"database/sql"
 	"fmt"
 	"log"
 	"regexp"
 	"strings"
 
+	// register in driver.
+	_ "github.com/jackc/pgx/stdlib"
+
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	"github.com/influxdata/telegraf/plugins/inputs/postgresql"
@@ -112,23 +116,24 @@ func (p *Postgresql) IgnoredColumns() map[string]bool {
 var localhost = "host=localhost sslmode=disable"
 
 func (p *Postgresql) Gather(acc telegraf.Accumulator) error {
-
-	var sql_query string
-	var query_addon string
-	var db_version int
-	var query string
-	var tag_value string
-	var meas_name string
+	var (
+		err         error
+		db          *sql.DB
+		sql_query   string
+		query_addon string
+		db_version  int
+		query       string
+		tag_value   string
+		meas_name   string
+	)
 
 	if p.Address == "" || p.Address == "localhost" {
 		p.Address = localhost
 	}
 
-	db, err := postgresql.Connect(p.Address)
-	if err != nil {
+	if db, err = sql.Open("pgx", p.Address); err != nil {
 		return err
 	}
-
 	defer db.Close()
 
 	// Retreiving the database version