Insert metric labels only if they are not already present to prevent primary key sequence growing on each data point insert. Due to concurrency we can still attempt insert but the effect of that should not be big

Author: niksajakovljevic

.gitignore

@@ -1,8 +1,9 @@
 *~
-/prometheus-postgresql-adapter
+/prometheus-postgresql-adapter*
 /vendor
 /version.properties
 /.target_os
 /.history
 /.vscode
+/.idea
 

Gopkg.lock

@@ -73,7 +73,7 @@ type Client struct {
 const (
 	sqlCreateTmpTable = "CREATE TEMPORARY TABLE IF NOT EXISTS %s_tmp(sample prom_sample) ON COMMIT DELETE ROWS;"
 	sqlCopyTable      = "COPY \"%s\" FROM STDIN"
-	sqlInsertLabels   = "INSERT INTO %s_labels (metric_name, labels) SELECT prom_name(tmp.sample), prom_labels(tmp.sample) FROM %s_tmp tmp ON CONFLICT (metric_name, labels) DO NOTHING;"
+	sqlInsertLabels   = "INSERT INTO %s_labels (metric_name, labels) SELECT tmp.prom_name, tmp.prom_labels FROM (SELECT prom_time(sample), prom_value(sample), prom_name(sample), prom_labels(sample) FROM %s_tmp) tmp LEFT JOIN %s_labels l ON tmp.prom_name=l.metric_name AND tmp.prom_labels=l.labels WHERE l.metric_name IS NULL ON CONFLICT (metric_name, labels) DO NOTHING;"
 	sqlInsertValues   = "INSERT INTO %s_values SELECT tmp.prom_time, tmp.prom_value, l.id FROM (SELECT prom_time(sample), prom_value(sample), prom_name(sample), prom_labels(sample) FROM %s_tmp) tmp INNER JOIN %s_labels l on tmp.prom_name=l.metric_name AND  tmp.prom_labels=l.labels;"
 )
 
@@ -256,7 +256,7 @@ func (c *Client) Write(samples model.Samples) error {
 	}
 
 	if copyTable == fmt.Sprintf("%s_tmp", c.cfg.table) {
-		stmtLabels, err := tx.Prepare(fmt.Sprintf(sqlInsertLabels, c.cfg.table, c.cfg.table))
+		stmtLabels, err := tx.Prepare(fmt.Sprintf(sqlInsertLabels, c.cfg.table, c.cfg.table, c.cfg.table))
 		if err != nil {
 			log.Error("msg", "Error on preparing labels statement", "err", err)
 			return err