Merge pull request #573 from cybertec-postgresql/make-distinct-dbname…

…-maintenance-less-costly

[+] make unique dbname maintenance less costly for multi-daemon setups, fixes #525

pgwatch2/pgwatch2.go

@@ -505,9 +505,9 @@ func InitAndTestMetricStoreConnection(connStr string, failOnErr bool) error {
 			break
 		}
 	}
-	metricDb.SetMaxIdleConns(1)
+	metricDb.SetMaxIdleConns(2)
 	metricDb.SetMaxOpenConns(2)
-	metricDb.SetConnMaxLifetime(time.Second * time.Duration(PG_CONN_RECYCLE_SECONDS))
+	metricDb.SetConnMaxLifetime(time.Second * 172800) // 2d
 	return nil
 }
 
@@ -1513,6 +1513,7 @@ func AddDBUniqueMetricToListingTable(db_unique, metric string) error {
 
 func UniqueDbnamesListingMaintainer(daemonMode bool) {
 	// due to metrics deletion the listing can go out of sync (a trigger not really wanted)
+	sql_get_advisory_lock := `SELECT pg_try_advisory_lock(1571543679778230000) AS have_lock` // 1571543679778230000 is just a random bigint
 	sql_top_level_metrics := `SELECT table_name FROM admin.get_top_level_metric_tables()`
 	sql_distinct := `
 	WITH RECURSIVE t(dbname) AS (
@@ -1534,6 +1535,17 @@ func UniqueDbnamesListingMaintainer(daemonMode bool) {
 			time.Sleep(time.Hour * 24)
 		}
 
+		log.Infof("Trying to get metricsDb listing maintaner advisory lock...") // to only have one "maintainer" in case of a "push" setup, as can get costly
+		lock, err := DBExecRead(metricDb, METRICDB_IDENT, sql_get_advisory_lock)
+		if err != nil {
+			log.Error("Getting metricsDb listing maintaner advisory lock failed:", err)
+			continue
+		}
+		if !(lock[0]["have_lock"].(bool)) {
+			log.Info("Skipping admin.all_distinct_dbname_metrics maintenance as another instance has the advisory lock...")
+			continue
+		}
+
 		log.Infof("Refreshing admin.all_distinct_dbname_metrics listing table...")
 		all_distinct_metric_tables, err := DBExecRead(metricDb, METRICDB_IDENT, sql_top_level_metrics)
 		if err != nil {