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参考：http://www.postgresql.org/docs/9.5/static/continuous-archiving.html
http://www.mkyong.com/database/postgresql-point-in-time-recovery-incremental-backup/
wal，即预写式日志，是日志的标准实现方式，简单而言就是将对数据库的变动记录到日志 中，而后在将具体的新数据刷新到磁盘。PostgreSQL将该日志维护在数据文件夹下的子文件夹pg_xlog中。当数据库崩溃后，可以通过“重放”日志中的“动作”，将数据库恢复。也就是说，只要拥有一个基础备份和完整的日志文件，理论上可以将数据库库恢复到任意基础备份以来的任意时刻点。不仅如此，如果在另一个实例上将这些日志不停的“重放”，那么就拥有了一个完整的在线备份，也就是“复制”。
pg_xlog下日志文件不会无限制增多，也就是说并不用担心日志的增多使得磁盘空间捉襟见肘。默认每个日志文件为16M大小，即当增长到16M时，就会切换到别的文件，并复用之前的文件 。因此，为了保证有个完整的日志链，必须将写满的文件复制保存到一个特定的文件 夹。对于最后一个还未满16M的日志文件，可以手动触发一次切换。
备份（操作均使用系统账号postgres完成 ）
postgres@debian:~$ psql psql (9.5.0) Type "help" for help. postgres=# CREATE DATABASE test; CREATE DATABASE
vim /etc/postgresql/9.5/main/postgresql.conf wal_level = archive archive_mode = on archive_command = ‘ test ! -f /var/lib/postgresql/archive/%f && cp %p /var/lib/postgresql/archive/%f‘
postgres@debian:~$ mkdir archive postgres@debian:~$ /usr/lib/postgresql/9.5/bin/pg_ctl restart -D /var/lib/postgresql/9.5/main/ -o "-c config_file=/etc/postgresql/9.5/main/postgresql.conf" 2016-01-18 09:30:42 CST [2937-2] LOG: received fast shutdown request 2016-01-18 09:30:42 CST [2937-3] LOG: aborting any active transactions 2016-01-18 09:30:42 CST [2942-2] LOG: autovacuum launcher shutting down 2016-01-18 09:30:42 CST [2939-1] LOG: shutting down waiting for server to shut down.....2016-01-18 09:30:44 CST [2939-2] LOG: database system is shut down done server stopped server starting postgres@debian:~$ 2016-01-18 09:30:45 CST [2972-1] LOG: database system was shut down at 2016-01-18 09:30:44 CST 2016-01-18 09:30:45 CST [2972-2] LOG: MultiXact member wraparound protections are now enabled 2016-01-18 09:30:45 CST [2971-1] LOG: database system is ready to accept connections 2016-01-18 09:30:45 CST [2976-1] LOG: autovacuum launcher started
postgres@debian:~$ psql psql (9.5.0) Type "help" for help. postgres=# \c test You are now connected to database "test" as user "postgres". test=# CREATE TABLE testPITR1 AS SELECT * FROM pg_class, pg_description; SELECT 1192063
psql -c "SELECT pg_start_backup(‘base‘, true)" cd /var/lib/postgresql/9.5/ tar -cvf main.tar main psql -c "SELECT pg_stop_backup()"
6. 继续创建测试表，切换日志
postgres@debian:~$ psql psql (9.5.0) Type "help" for help. postgres=# \c test You are now connected to database "test" as user "postgres". test=# CREATE TABLE testPITR2 AS SELECT * FROM pg_class, pg_description; SELECT 1203562 test=# select * from current_timestamp; now ------------------------------- 2016-01-18 10:02:15.229335+08 (1 row) test=# CREATE TABLE testPITR3 AS SELECT * FROM pg_class, pg_description; SELECT 1215061 test=# select * from current_timestamp; now ------------------------------- 2016-01-18 10:02:51.029447+08 (1 row) test=# select pg_switch_xlog(); pg_switch_xlog ---------------- 0/3DDE6750 (1 row)
恢复
关闭数据库，模拟数据库宕机，此时，数据库test中应该有3张表，其中1张表在基础备份前，也就是恢复完数据文件即可找回，而另2张表则需恢复相应的日志文件。模拟恢复到testPITR2创建时刻点。
postgres@debian:~$ /usr/lib/postgresql/9.5/bin/pg_ctl stop -D /var/lib/postgresql/9.5/main/ 2016-01-18 10:06:12 CST [2971-2] LOG: received fast shutdown request 2016-01-18 10:06:12 CST [2971-3] LOG: aborting any active transactions 2016-01-18 10:06:12 CST [2976-2] LOG: autovacuum launcher shutting down 2016-01-18 10:06:12 CST [2973-1] LOG: shutting down waiting for server to shut down.....2016-01-18 10:06:13 CST [2973-2] LOG: database system is shut down done server stopped postgres@debian:~$ mv 9.5/main 9.5/main.old
postgres@debian:~$cd /var/lib/postgresql/9.5/ postgres@debian:~/9.5$ tar -xvf 9.5/main.tar postgres@debian:~$ 2016-01-18 10:26:40 CST [3342-1] LOG: database system was interrupted; last known up at 2016-01-18 09:54:56 CST 2016-01-18 10:26:40 CST [3342-2] LOG: redo starts at 0/17000098 2016-01-18 10:26:40 CST [3342-3] LOG: invalid record length at 0/17009348 2016-01-18 10:26:40 CST [3342-4] LOG: redo done at 0/170092D8 2016-01-18 10:26:40 CST [3342-5] LOG: last completed transaction was at log time 2016-01-18 09:48:26.585085+08 2016-01-18 10:26:40 CST [3342-6] LOG: MultiXact member wraparound protections are now enabled 2016-01-18 10:26:40 CST [3341-1] LOG: database system is ready to accept connections 2016-01-18 10:26:40 CST [3346-1] LOG: autovacuum launcher started postgres@debian:~$ psql psql (9.5.0) Type "help" for help. postgres=# \c test You are now connected to database "test" as user "postgres". test=# \d List of relations Schema | Name | Type | Owner --------+-----------+-------+---------- public | testpitr1 | table | postgres (1 row)
vi recovery.conf restore_command = ‘cp /var/lib/postgresql/archive/%f %p‘ recovery_target_time = ‘2016-01-18 10:02:15‘ postgres@debian:~/9.5/main$ /usr/lib/postgresql/9.5/bin/pg_ctl start -D /var/lib/postgresql/9.5/main/ -o "-c config_file=/etc/postgresql/9.5/main/postgresql.conf" -l /var/lib/postgresql/recovery.log
可以在恢复日志中看到这么一句话：
2016-01-18 11:22:39 CST [1743-44] LOG: recovery stopping before commit of transaction 630, time 2016-01-18 10:02:46.080443+08
postgres@debian:~$ psql psql (9.5.0) Type "help" for help. postgres=# \c test You are now connected to database "test" as user "postgres". test=# \dt List of relations Schema | Name | Type | Owner --------+-----------+-------+---------- public | testpitr1 | table | postgres public | testpitr2 | table | postgres (2 rows)
如果需要恢复table3，则必须再次删除数据文件夹，建立recovery.conf。
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原文地址：http://www.cnblogs.com/cxy486/p/5140262.html
