PostgreSQL恢复误删数据

　　在Oracle中；删除表或者误删表记录；有个闪回特性，不需要停机操作，可以完美找回记录。当然也有一些其他的恢复工具；例如odu工具，gdul工具。都可以找回数据。而PostgreSQL目前没有闪回特性。如何在不停机情况下恢复误删数据。还好是有完整的热备份。

　　本文描述的方法是：利用热备份在另一台服务器进行数据恢复；再导入正式环境；这样不影响数据库操作。这方法也适用在Oracle恢复。必须满足几个条件

有完整的基础数据文件备份和归档文件备份.所以备份是很重要的。
有一台装好同款Postgres软件的服务器

实例模拟讲解

　　过程模拟误删表tbl_lottu_drop后；后续进行dml/ddl操作；表明正式数据库还是进行正常工作。在另外一台数据库基于数据库PITR恢复。恢复表tbl_lottu_drop的数据。

Postgres201 ：线上数据库服务器
Postgres202 ：操作服务器

1. 创建一个有效的备份

postgres=# select pg_start_backup(now()::text);

 pg_start_backup

-----------------

 0/F000060

(1 row)

[postgres@Postgres201 ~]$ rsync -acvz -L --exclude "pg_xlog" --exclude "pg_log" $PGDATA /data/backup/20180428

postgres=# select pg_stop_backup();

NOTICE:  pg_stop_backup complete, all required WAL segments have been archived

 pg_stop_backup

----------------

 0/F000168

(1 row)

2. 模拟误操作

　　2.1 创建一个需要恢复对象表tbl_lottu_drop。并插入1000记录。也保证数据从数据缓存写入磁盘中。

lottu=> create table tbl_lottu_drop (id int);

CREATE TABLE

lottu=> insert into tbl_lottu_drop select generate_series(1,1000);

INSERT 0 1000

lottu=> \c lottu postgres

You are now connected to database "lottu" as user "postgres".

　　2.2 这个获取一个时间：用于后面基于数据库PITR恢复(当然现实操作后只能记住一个大概的时间；还往往是不准；可能记住的时间是误操作之后。后面有讲解如何获取需要恢复到那个时间点)

lottu=# select now();

              now

-------------------------------

 2018-04-28 20:47:31.617808+08

(1 row)

lottu=# checkpoint;

CHECKPOINT

lottu=# select pg_xlogfile_name(pg_switch_xlog());

     pg_xlogfile_name

--------------------------

 000000030000000000000010

(1 row)

　　2.3 进行drop表

lottu=# drop table tbl_lottu_drop;

DROP TABLE

　　2.4 后续进行dml/ddl操作；表明正式数据库还是进行正常工作

lottu=# create table tbl_lottu_log (id int);

CREATE TABLE

lottu=# insert into  tbl_lottu_log values (1),(2);

INSERT 0 2

lottu=# checkpoint;

CHECKPOINT

lottu=# select pg_xlogfile_name(pg_switch_xlog());

     pg_xlogfile_name

--------------------------

 000000030000000000000011

(1 row)

3. 恢复操作

　　3.1 将备份拷贝到Postgres202数据库上

[postgres@Postgres201 20180428]$ cd /data/backup/20180428

[postgres@Postgres201 20180428]$ ll

total 4

drwx------. 18 postgres postgres 4096 Apr 28 20:42 data

[postgres@Postgres201 20180428]$ rsync -acvz -L data postgres@192.168.1.202:/data/postgres

　　3.2 删除不必要的文件

[postgres@Postgres202 data]$ cd $PGDATA

[postgres@Postgres202 data]$ rm backup_label.old postmaster.pid tablespace_map.old

　　3.3 还原备份表空间软链接

[postgres@Postgres202 data]$ cat tablespace_map

16385 /data/pg_data/lottu

[postgres@Postgres202 data]$ mkdir -p /data/pg_data

[postgres@Postgres202 data]$ cd pg_tblspc/

[postgres@Postgres202 pg_tblspc]$ mv 16385/  /data/pg_data/lottu

[postgres@Postgres202 pg_tblspc]$ ln -s /data/pg_data/lottu ./16385

[postgres@Postgres202 pg_tblspc]$ ll

total 0

lrwxrwxrwx. 1 postgres postgres 19 Apr 28 23:12 16385 -> /data/pg_data/lottu

　　3.4 将wal日志拷贝到Postgres202数据库上pg_xlog目录下；从哪个日志开始拷贝？

[postgres@Postgres202 data]$ mkdir -p pg_xlog/archive_status

[postgres@Postgres202 data]$ cat backup_label

START WAL LOCATION: 0/F000060 (file 00000003000000000000000F)

CHECKPOINT LOCATION: 0/F000098

BACKUP METHOD: pg_start_backup

BACKUP FROM: master

START TIME: 2018-04-28 20:42:15 CST

LABEL: 2018-04-28 20:42:13.244358+08

　　查看backup_label；知道00000003000000000000000F开始到正在写入的wal日志。

[postgres@Postgres202 pg_xlog]$ ll

total 65540

-rw-------. 1 postgres postgres 16777216 Apr 28 20:42 00000003000000000000000F

-rw-------. 1 postgres postgres      313 Apr 28 20:42 00000003000000000000000F.00000060.backup

-rw-------. 1 postgres postgres 16777216 Apr 28 20:48 000000030000000000000010

-rw-------. 1 postgres postgres 16777216 Apr 28 20:50 000000030000000000000011

-rw-------. 1 postgres postgres 16777216 Apr 28 20:55 000000030000000000000012

　　3.5 编辑recovery.conf文件

[postgres@Postgres202 data]$ vi recovery.conf 

restore_command = 'cp /data/arch/%f %p'            # e.g. 'cp /mnt/server/archivedir/%f %p'

recovery_target_time = '2018-04-28 20:47:31.617808+08'

recovery_target_inclusive = false

recovery_target_timeline = 'latest'

　　3.6 启动数据库；并验证数据

[postgres@Postgres202 data]$ pg_start

server starting

[postgres@Postgres202 data]$ ps -ef | grep postgres

root      1098  1083  0 22:32 pts/0    00:00:00 su - postgres

postgres  1099  1098  0 22:32 pts/0    00:00:00 -bash

root      1210  1195  0 22:55 pts/1    00:00:00 su - postgres

postgres  1211  1210  0 22:55 pts/1    00:00:00 -bash

postgres  1442     1  1 23:16 pts/0    00:00:00 /opt/pgsql96/bin/postgres

postgres  1450  1442  0 23:16 ?        00:00:00 postgres: checkpointer process

postgres  1451  1442  0 23:16 ?        00:00:00 postgres: writer process

postgres  1459  1442  0 23:16 ?        00:00:00 postgres: wal writer process

postgres  1460  1442  0 23:16 ?        00:00:00 postgres: autovacuum launcher process

postgres  1461  1442  0 23:16 ?        00:00:00 postgres: archiver process   last was 00000005.history

postgres  1462  1442  0 23:16 ?        00:00:00 postgres: stats collector process

postgres  1464  1099  0 23:16 pts/0    00:00:00 ps -ef

postgres  1465  1099  0 23:16 pts/0    00:00:00 grep postgres

[postgres@Postgres202 data]$ psql

psql (9.6.0)

Type "help" for help.

postgres=# \c lottu lottu

You are now connected to database "lottu" as user "lottu".

lottu=> \dt

            List of relations

 Schema |      Name      | Type  | Owner

--------+----------------+-------+-------

 public | pitr_test      | table | lottu

 public | tbl_lottu_drop | table | lottu

 lottu=> select count(1) from tbl_lottu_drop;

 count

-------

  1000

(1 row)

　　从这看数据是恢复了；copy到线上数据库操作略。

延伸点

下面讲解下如何找到误操作的时间。即recovery_target_time = '2018-04-28 20:47:31.617808+08'的时间点。上文是前面已经获取的；

　　1. 用pg_xlogdump解析这段日志。

[postgres@Postgres201 pg_xlog]$ pg_xlogdump -b 00000003000000000000000F 000000030000000000000012 > lottu.log

pg_xlogdump: FATAL:  error in WAL record at 0/12000648: invalid record length at 0/12000680: wanted 24, got 0

　　2. 从lottu.log中可以找到这段日志

rmgr: Transaction len (rec/tot):      8/    34, tx:       1689, lsn: 0/100244A0, prev 0/10024460, desc: COMMIT 2018-04-28 20:45:49.736013 CST

rmgr: Standby     len (rec/tot):     24/    50, tx:          0, lsn: 0/100244C8, prev 0/100244A0, desc: RUNNING_XACTS nextXid 1690 latestCompletedXid 1689 oldestRunningXid 1690

rmgr: Heap        len (rec/tot):      3/  3130, tx:       1690, lsn: 0/10024500, prev 0/100244C8, desc: INSERT off 9

    blkref #0: rel 16385/16386/2619 fork main blk 15 (FPW); hole: offset: 60, length: 5116

rmgr: Btree       len (rec/tot):      2/  7793, tx:       1690, lsn: 0/10025140, prev 0/10024500, desc: INSERT_LEAF off 385

    blkref #0: rel 16385/16386/2696 fork main blk 1 (FPW); hole: offset: 1564, length: 452

rmgr: Heap        len (rec/tot):      2/   184, tx:       1690, lsn: 0/10026FD0, prev 0/10025140, desc: INPLACE off 16

    blkref #0: rel 16385/16386/1259 fork main blk 0

rmgr: Transaction len (rec/tot):     88/   114, tx:       1690, lsn: 0/10027088, prev 0/10026FD0, desc: COMMIT 2018-04-28 20:46:37.718442 CST; inval msgs: catcache 49 catcache 45 catcache 44 relcache 32784

rmgr: Standby     len (rec/tot):     24/    50, tx:          0, lsn: 0/10027100, prev 0/10027088, desc: RUNNING_XACTS nextXid 1691 latestCompletedXid 1690 oldestRunningXid 1691

rmgr: Standby     len (rec/tot):     24/    50, tx:          0, lsn: 0/10027138, prev 0/10027100, desc: RUNNING_XACTS nextXid 1691 latestCompletedXid 1690 oldestRunningXid 1691

rmgr: XLOG        len (rec/tot):     80/   106, tx:          0, lsn: 0/10027170, prev 0/10027138, desc: CHECKPOINT_ONLINE redo 0/10027138; tli 3; prev tli 3; fpw true; xid 0:1691; oid 40976; multi 1; offset 0; oldest xid 1668 in DB 1; oldest multi 1 in DB 1; oldest/newest commit timestamp xid: 0/0; oldest running xid 1691; online

rmgr: Standby     len (rec/tot):     24/    50, tx:          0, lsn: 0/100271E0, prev 0/10027170, desc: RUNNING_XACTS nextXid 1691 latestCompletedXid 1690 oldestRunningXid 1691

rmgr: Standby     len (rec/tot):     24/    50, tx:          0, lsn: 0/10027218, prev 0/100271E0, desc: RUNNING_XACTS nextXid 1691 latestCompletedXid 1690 oldestRunningXid 1691

rmgr: XLOG        len (rec/tot):     80/   106, tx:          0, lsn: 0/10027250, prev 0/10027218, desc: CHECKPOINT_ONLINE redo 0/10027218; tli 3; prev tli 3; fpw true; xid 0:1691; oid 40976; multi 1; offset 0; oldest xid 1668 in DB 1; oldest multi 1 in DB 1; oldest/newest commit timestamp xid: 0/0; oldest running xid 1691; online

rmgr: XLOG        len (rec/tot):      0/    24, tx:          0, lsn: 0/100272C0, prev 0/10027250, desc: SWITCH

rmgr: Standby     len (rec/tot):     24/    50, tx:          0, lsn: 0/11000028, prev 0/100272C0, desc: RUNNING_XACTS nextXid 1691 latestCompletedXid 1690 oldestRunningXid 1691

rmgr: Standby     len (rec/tot):     16/    42, tx:       1691, lsn: 0/11000060, prev 0/11000028, desc: LOCK xid 1691 db 16386 rel 32784

rmgr: Heap        len (rec/tot):      8/  2963, tx:       1691, lsn: 0/11000090, prev 0/11000060, desc: DELETE off 16 KEYS_UPDATED

    blkref #0: rel 16385/16386/1247 fork main blk 8 (FPW); hole: offset: 88, length: 5288

根据“32784”日志可以看到是表tbl_lottu_drop在2018-04-28 20:46:37.718442插入1000条记录(所以恢复时间点选2018-04-28 20:47:31.617808+08没毛病)；即也是在事务id为1690操作的。并在事务id为1691进行删除操作。

所以上面的recovery.conf 也可以改写为：

restore_command = 'cp /data/arch/%f %p'            # e.g. 'cp /mnt/server/archivedir/%f %p'

recovery_target_xid = '1690'

recovery_target_inclusive = false

recovery_target_timeline = 'latest'