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pg_rewind

DB之路 2021-04-20
1050

  pg_rewind是postgresql主丛数据库之同步数据目录的工具。需要目标服务器在postgresql.conf 中允许wal_log_hints,或者在 initdb初始化集群时允许 checksums ,full_page_writes也必须为on


  pg_rewind只复制表数据文件中更改的块;所有其他文件都被完整复制,包括配置文件。pg_rewind相对于使用pg_basebackup备份或rsync等工具的优势在于,pg_rewind不需要读取数据库中未更改的块。这使得在数据库很大且之间只有一小部分块不同的情况下,速度会快得多。


  pg_rewind [option...] { -D | --target-pgdata } directory { --source-pgdata=directory | --source-server=connstr


参数:


-D directory --target-pgdata=directory


  此选项指定与源同步的目标数据目录。在运行pg_rewind之前,必须干净关闭目标服务器


--source-pgdata=directory


  指定要与之同步的源服务器的数据目录的文件系统路径。此选项要求干净关闭源服务器


--source-server=connstr


  指定要连接到源PostgreSQL服务器的libpq连接字符串。连接必须是具有超级用户访问权限的正常(非复制)连接。此选项要求源服务器正在运行,而不是处于恢复模式。


-n --dry-run


  除了实际修改目标目录之外,执行所有操作。


-P --progress


  使进展报告。


实验使用两台主机,都安装postgresql-13.1,已配置流复制


主:192.168.56.5 m1


丛:192.168.56.25 m7


m1(主):创建测试表和数据


postgres=# create table test (id int,e_name varchar(100),e_mail varchar(100),d_id int);

CREATE TABLE

postgres=# \d

List of relations

Schema | Name | Type | Owner

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

public | test | table | postgres

(1 row)

postgres=# insert into test values(1,'zbs','123@126.com',10);

INSERT 0 1

postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

(1 row)

m7 (丛):查询数据复制成功


[postgres@z_leader ~]$ psql postgres

psql (13.1)

Type "help" for help.

postgres=# \d

List of relations

Schema | Name | Type | Owner

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

public | test | table | postgres

(1 row)

postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

(1 row)

提升丛库为新主库


[postgres@z_leader data]$ pg_ctl promote -D usr/local/pg/data

waiting for server to promote.... done

server promoted

[postgres@z_leader data]$ psql postgres

psql (13.1)

Type "help" for help.

postgres=# select pg_is_in_recovery();

pg_is_in_recovery

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

f

(1 row)

m1(原主库)插入一条记录,模拟原主库上的数据没有复制到原丛库上


postgres=# insert into test values(2,'zbs1','124@126.com',10);

INSERT 0 1

postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

2 | zbs1 | 124@126.com | 10

(2 rows)

m7:在原丛库上(已提升为主库)插入一条记录并查看结果


postgres=# insert into test values(3,'zbs2','124@126.com',10);

INSERT 0 1

postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

3 | zbs2 | 124@126.com | 10

(2 rows)

m1 将原主库变为新主库的丛库


[postgres@localhost ~]$ kill -INT `head -1 usr/local/pg/data/postmaster.pid`

--配置流复制文件和参数


[postgres@localhost data]$ mv recovery.done recovery.conf

[postgres@localhost data]$ cat recovery.conf

standby_mode = 'on'

restore_command = 'cp usr/local/pg/arch/%f'

primary_conninfo = 'host=192.168.56.25 port=5432 user=rep'

recovery_target_timeline = 'latest'

[postgres@localhost data]$

--启动数据库


[postgres@localhost ~]$ usr/local/pg/bin/pg_ctl -D usr/local/pg/data -l logfile start

waiting for server to start.... done

server started

[postgres@localhost data]$ psql postgres

psql (13.1)

Type "help" for help.

postgres=# select pg_is_in_recovery();

pg_is_in_recovery

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

t

(1 row)

postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

2 | zbs1 | 124@126.com | 10

(2 rows)

--在m7上插入的记录未能复制过来


---日志信息


2020-11-19 09:15:17.415 CST [2492] LOG: consistent recovery state reached at 0/D000098

2020-11-19 09:15:17.415 CST [2492] LOG: invalid record length at 0/D000098: wanted 24, got 0

2020-11-19 09:15:17.415 CST [2490] LOG: database system is ready to accept read only connections

2020-11-19 09:15:17.429 CST [2500] LOG: fetching timeline history file for timeline 6 from primary server

2020-11-19 09:15:17.460 CST [2500] FATAL: could not start WAL streaming: ERROR: requested starting point 0/D000000 on timeline 5 is not in this

server's history

DETAIL: This server's history forked from timeline 5 at 0/C003168.

cp: missing destination file operand after `/usr/local/pg/arch/00000006.history'

Try `cp --help' for more information.

cp: missing destination file operand after `/usr/local/pg/arch/00000007.history'

Try `cp --help' for more information.

cp: missing destination file operand after `/usr/local/pg/arch/00000006.history'

Try `cp --help' for more information.

2020-11-19 09:15:17.469 CST [2492] LOG: new timeline 6 forked off current database system timeline 5 before current recovery point 0/D000098

cp: missing destination file operand after `/usr/local/pg/arch/00000005000000000000000D



[postgres@localhost ~]$ kill -INT `head -1 usr/local/pg/data/postmaster.pid`

---使得pg_rewind 同步数据库时间线


[[postgres@localhost ~]$ pg_rewind --target-pgdata /usr/local/pg/data --source-server='host=192.168.56.25 port=5432 user=postgres dbname=postgres' -P

connected to server

servers diverged at WAL location 0/C003168 on timeline 5

rewinding from last common checkpoint at 0/C003010 on timeline 5

reading source file list

reading target file list

reading WAL in target

need to copy 100 MB (total source directory size is 118 MB)

102599/102599 kB (100%) copied

creating backup label and updating control file

syncing target data directory

Done!

--pg_rewind后此文件需要重新配置


[postgres@localhost data]$ cat recovery.conf

standby_mode = 'on'

restore_command = 'cp /usr/local/pg/arch/%f'

primary_conninfo = 'host=192.168.56.25 port=5432 user=rep'

recovery_target_timeline = 'latest'



[postgres@localhost ~]$ /usr/local/pg/bin/pg_ctl -D /usr/local/pg/data -l logfile start

waiting for server to start.... done

server started

[postgres@localhost ~]$ psql postgres

psql (13.1)

Type "help" for help.

postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

3 | zbs2 | 124@126.com | 10

(2 rows)

postgres=# select pg_is_in_recovery();

pg_is_in_recovery

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

t

(1 row)

--原主库没有复制到丛库的记录消失,在新主库上插入的记录已同步


m7(新主库)

[postgres@z_leader ~]$ psql postgres

psql (13.1)

Type "help" for help.

postgres=# insert into test values(4,'zbs2','124@126.com',10);

INSERT 0 1

postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

3 | zbs2 | 124@126.com | 10

4 | zbs2 | 124@126.com | 10

(3 rows)

m1(新丛库)


postgres=# select * from test;

id | e_name | e_mail | d_id

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

1 | zbs | 123@126.com | 10

3 | zbs2 | 124@126.com | 10

4 | zbs2 | 124@126.com | 10

(3 rows)


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