1/*
2** Zabbix
3** Copyright (C) 2001-2021 Zabbix SIA
4**
5** This program is free software; you can redistribute it and/or modify
6** it under the terms of the GNU General Public License as published by
7** the Free Software Foundation; either version 2 of the License, or
8** (at your option) any later version.
9**
10** This program is distributed in the hope that it will be useful,
11** but WITHOUT ANY WARRANTY; without even the implied warranty of
12** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13** GNU General Public License for more details.
14**
15** You should have received a copy of the GNU General Public License
16** along with this program; if not, write to the Free Software
17** Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
18**/
19
20package postgres
21
22import (
23	"context"
24	"errors"
25
26	"github.com/jackc/pgx/v4"
27	"zabbix.com/pkg/zbxerr"
28)
29
30// oldestXIDHandler gets age of the oldest xid if all is OK or nil otherwise.
31func oldestXIDHandler(ctx context.Context, conn PostgresClient,
32	_ string, _ map[string]string, _ ...string) (interface{}, error) {
33	var resultXID int64
34
35	query := `SELECT greatest(max(age(backend_xmin)), max(age(backend_xid)))
36				FROM pg_catalog.pg_stat_activity`
37
38	row, err := conn.QueryRow(ctx, query)
39	if err != nil {
40		return nil, zbxerr.ErrorCannotFetchData.Wrap(err)
41	}
42
43	err = row.Scan(&resultXID)
44	if err != nil {
45		if errors.Is(err, pgx.ErrNoRows) {
46			return nil, zbxerr.ErrorEmptyResult.Wrap(err)
47		}
48
49		return nil, zbxerr.ErrorCannotFetchData.Wrap(err)
50	}
51
52	return resultXID, nil
53}
54