PostgreSQL基於時間點恢復(PITR)

數據庫的PITR是通常數據庫都必須知足的技術。其原理是依據以前的物理備份文件加上wal的預寫日誌模式備份作的恢復。該技術支持8.*及以上版本。下面主要概述PITR的準備和恢復過程。 測試環境

OS 環境：CentOS 6.2
數據庫 ：PostgreSQL 9.1.3
pg_home=/home/postgres/
pg_data=/database/pgdata/

1、前期工做既要恢復，確定是須要一個備份基礎的，不然再怎麼的巧婦也難爲無米之炊。
1.修改數據庫參數，修改postgresql.conf：

archive_mode = on
archive_timeout = 300   --單位是秒，此處以5分鐘爲限強制歸檔，僅做測試
archive_command = 'cp -i %p /home/postgres/archive/%f'
wal_level = archive

修改完重啓下reload,DB

2.基於文件級別的持續備份，
a.基礎備份
postgres=# select pg_start_backup('backup_2012_05_20_14:22:10');

b.打包備份pg_data
# cd /database
# tar -cvzf pgdata.tar ./pgdata

c.結束基礎備份並切換歸檔

postgres=# select pg_stop_backup();

postgres=# select pg_switch_xlog();
 pg_switch_xlog 
----------------
 0/C000020
(1 row)

postgres=# select pg_current_xlog_location();
 pg_current_xlog_location 
--------------------------
 0/C000020
(1 row)

postgres=# create table test_1(id int,name varchar(50));
postgres=# insert into test_1 values (1,'kenyon');
INSERT 0 1

此時在pg_data路徑下會產生一個label,能夠查看內容有checkpoint時間,基礎備份的開始和結束時間，以及標籤名稱等。由於以前已經設置了archive的三個參數，能夠在archive的備份路徑pg_home/archive下看到歸檔的文件會定時傳過來。

2、恢復過程
停數據庫
# pg_stop

假定數據庫的崩潰場景，將pgdata數據刪除
# rm -rf /database/pgdata

恢復以前備份的tar文件
# tar xvf pgdata.tar

刪除pg_xlog文件夾並重建
# rm -rf pg_xlog # mkdir -p pg_xlog/archive_status

拷貝recovery.conf文件並修改
# cp $PG_HOME/recovery.conf.sample /database/pgdata/
# vi /database/pgdata/recovery.conf
--新增內容，指定恢復文件和路徑，%f,%p見上面說明
restore_command = 'cp /home/postgres/archive/%f "%p"'

啓動數據庫

# pg_start
[postgres@localhost archive]$ psql
spsql (9.1.3)
Type "help" for help.

postgres=# select * from test_1;
 id |  name  
----+--------
  1 | kenyon
(1 rows)

--恢復成功，會恢復到以前接收到的最後一個歸檔文件。另外recovery.conf會更名變成recovery.done

日誌內容:

LOG:  shutting down
LOG:  database system is shut down
LOG:  database system was interrupted; last known up at 2012-05-20 22:23:15 CST
LOG:  starting archive recovery
LOG:  restored log file "000000010000000000000002" from archive
LOG:  redo starts at 0/8000078
LOG:  consistent recovery state reached at 0/C000000
LOG:  restored log file "000000010000000000000003" from archive
LOG:  restored log file "000000010000000000000004" from archive
LOG:  restored log file "000000010000000000000005" from archive
LOG:  restored log file "000000010000000000000006" from archive
LOG:  restored log file "000000010000000000000007" from archive
cp: cannot stat `/home/postgres/archive/000000010000000000000008': No such file or directory
LOG:  could not open file "pg_xlog/000000010000000000000008" (log file 0, segment 8): No such file or directory
LOG:  redo done at 0/1C000078
LOG:  last completed transaction was at log time 2012-05-20 23:01:22.960591+08
LOG:  restored log file "000000010000000000000007" from archive
cp: cannot stat `/home/postgres/archive/00000002.history': No such file or directory
LOG:  selected new timeline ID: 2
cp: cannot stat `/home/postgres/archive/00000001.history': No such file or directory
LOG:  archive recovery complete
LOG:  database system is ready to accept connections
LOG:  autovacuum launcher started

PS:若要恢復到指定時間，還須要再recovery.conf中設置recovrey_target_time,recovery_target_timeline等參數

總結：pitr技術對於7*24小時支撐是相當重要的，可是若是數據庫很是小，增大pg_dump備份的頻率可能更方便，但對於大數據庫就須要了。