PostgreSQL基于时间点恢复(PITR)
数据库的PITR是一般数据库都必须满足的技术。其原理是依据之前的物理备份文件加上wal的预写日志模式备份做的恢复。该技术支持8.*及以上版本。下面主要概述PITR的准备和恢复过程。 测试环境
OS 环境：CentOS 6.2数据库 ：PostgreSQL 9.1.3pg_home=/home/postgres/
pg_data=/database/pgdata/
一、前期工作既要恢复，肯定是需要一个备份基础的，否则再怎么的巧妇也难为无米之炊。
1.修改数据库参数，修改postgresql.conf：
archive_mode = onarchive_timeout = 300 --单位是秒，此处以5分钟为限强制归档，仅作测试archive_command = 'cp -i %p /home/postgres/archive/%f'wal_level = archive
修改完重启下reload,DB
2.基于文件级别的持续备份，
a.基础备份
postgres=# select pg_start_backup('backup_2012_05_20_14:22:10');
b.打包备份pg_data
# cd /database
# tar -cvzf pgdata.tar ./pgdata
c.结束基础备份并切换归档
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
此时在pg_data路径下会产生一个label,可以查看内容有checkpoint时间,基础备份的开始和结束时间，以及标签名称等。因为之前已经设置了archive的三个参数，可以在archive的备份路径pg_home/archive下看到归档的文件会定时传过来。
二、恢复过程
停数据库
# pg_stop
假定数据库的崩溃场景，将pgdata数据删除
# rm -rf /database/pgdata
恢复之前备份的tar文件
# tar xvf pgdata.tar
删除pg_xlog文件夹并重建
# rm -rf pg_xlog # mkdir -p pg_xlog/archive_status
拷贝recovery.conf文件并修改
# cp $PG_HOME/recovery.conf.sample /database/pgdata/
# vi /database/pgdata/recovery.conf
--新增内容，指定恢复文件和路径，%f,%p见上面说明
restore_command = 'cp /home/postgres/archive/%f "%p"'
启动数据库
# pg_start[postgres@localhost archive]$ psql
spsql (9.1.3)
Type "help" for help.
postgres=# select * from test_1;
id | name
----+--------
1 | kenyon
(1 rows)
--恢复成功，会恢复到之前接收到的最后一个归档文件。另外recovery.conf会改名变成recovery.done
日志内容:
LOG: shutting downLOG: database system is shut downLOG: database system was interrupted; last known up at 2012-05-20 22:23:15 CSTLOG: starting archive recoveryLOG: restored log file "000000010000000000000002" from archiveLOG: redo starts at 0/8000078LOG: consistent recovery state reached at 0/C000000LOG: restored log file "000000010000000000000003" from archiveLOG: restored log file "000000010000000000000004" from archiveLOG: restored log file "000000010000000000000005" from archiveLOG: restored log file "000000010000000000000006" from archiveLOG: restored log file "000000010000000000000007" from archivecp: 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 directoryLOG: selected new timeline ID: 2cp: cannot stat `/home/postgres/archive/00000001.history': No such file or directoryLOG: archive recovery completeLOG: database system is ready to accept connectionsLOG: autovacuum launcher started
PS:若要恢复到指定时间，还需要再recovery.conf中设置recovrey_target_time,recovery_target_timeline等参数
总结：pitr技术对于7*24小时支撑是至关重要的，但是如果数据库非常小，增大pg_dump备份的频率可能更方便，但对于大数据库就需要了。
