PostgreSQL恢复系列:pg_control异常恢复

发表于 2022 年 5 月 30 日 由 惜分飞

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标题：PostgreSQL恢复系列:pg_control异常恢复

作者：惜分飞©版权所有[未经本人同意,不得以任何形式转载,否则有进一步追究法律责任的权利.]

在PG中pg_control文件类似oracle数据库的control文件(控制文件),在Oracle中如果该文件丢失/损坏,可以通过alter database create controlfile命令进行创建,对于PG数据库来说也可以通过pg_resetwal命令来实现创建,由于pg_control文件损坏,需要人工指定一些参数完成pg_resetwal相关操作
pg_resetwal 使用说明

-bash-4.2$ pg_resetwal --help
pg_resetwal resets the PostgreSQL write-ahead log.

Usage:
  pg_resetwal [OPTION]... DATADIR

Options:
  -c, --commit-timestamp-ids=XID,XID
                                   set oldest and newest transactions bearing
                                   commit timestamp (zero means no change)
 [-D, --pgdata=]DATADIR            data directory
  -e, --epoch=XIDEPOCH             set next transaction ID epoch
  -f, --force                      force update to be done
  -l, --next-wal-file=WALFILE      set minimum starting location for new WAL
  -m, --multixact-ids=MXID,MXID    set next and oldest multitransaction ID
  -n, --dry-run                    no update, just show what would be done
  -o, --next-oid=OID               set next OID
  -O, --multixact-offset=OFFSET    set next multitransaction offset
  -u, --oldest-transaction-id=XID  set oldest transaction ID
  -V, --version                    output version information, then exit
  -x, --next-transaction-id=XID    set next transaction ID
      --wal-segsize=SIZE           size of WAL segments, in megabytes
  -?, --help                       show this help, then exit

Report bugs to <pgsql-bugs@lists.postgresql.org>.
PostgreSQL home page: <https://www.postgresql.org/>

确认现在业务表记录情况

-bash-4.2$ psql
psql (14.3)
Type "help" for help.

postgres=# select count(1) from ac_event;
 count  
--------
 246266
(1 row)

模拟pg_control文件异常

-bash-4.2$ ps -ef|grep postgres
postgres  37178      1  0 09:58 ?        00:00:00 /usr/pgsql-14/bin/postgres -D /var/lib/pgsql/14/data
postgres  37179  37178  0 09:58 ?        00:00:00 postgres: logger 
postgres  37181  37178  0 09:58 ?        00:00:00 postgres: checkpointer 
postgres  37182  37178  0 09:58 ?        00:00:00 postgres: background writer 
postgres  37183  37178  0 09:58 ?        00:00:00 postgres: walwriter 
postgres  37184  37178  0 09:58 ?        00:00:00 postgres: autovacuum launcher 
postgres  37185  37178  0 09:58 ?        00:00:00 postgres: stats collector 
postgres  37186  37178  0 09:58 ?        00:00:00 postgres: logical replication launcher 
root      41368  41314  0 11:06 pts/1    00:00:00 su - postgres
postgres  41369  41368  0 11:06 pts/1    00:00:00 -bash
postgres  45071  41369  0 12:07 pts/1    00:00:00 ps -ef
postgres  45072  41369  0 12:07 pts/1    00:00:00 grep --color=auto postgres
-bash-4.2$ kill -9 37178
-bash-4.2$ ps -ef|grep postgres
root      41368  41314  0 11:06 pts/1    00:00:00 su - postgres
postgres  41369  41368  0 11:06 pts/1    00:00:00 -bash
postgres  45095  41369  0 12:08 pts/1    00:00:00 ps -ef
postgres  45096  41369  0 12:08 pts/1    00:00:00 grep --color=auto postgres
-bash-4.2$ pwd
/var/lib/pgsql/14/data/global
-bash-4.2$ ls -l pg_control 
-rw-------. 1 postgres postgres 8192 May 30 12:04 pg_control
-bash-4.2$ rm -rf pg_control 
-bash-4.2$ ls -l pg_control 
ls: cannot access pg_control: No such file or directory

PG启动失败

-bash-4.2$ pg_ctl start 
pg_ctl: another server might be running; trying to start server anyway
waiting for server to start....postgres: could not find the database system
Expected to find it in the directory "/var/lib/pgsql/14/data",
but could not open file "/var/lib/pgsql/14/data/global/pg_control": No such file or directory
 stopped waiting
pg_ctl: could not start server
Examine the log output.

创建空pg_control文件启动依旧失败

-bash-4.2$ touch /var/lib/pgsql/14/data/global/pg_control
-bash-4.2$ pg_ctl start 
pg_ctl: another server might be running; trying to start server anyway
waiting for server to start....2022-05-30 12:09:43.953 CST [45215] PANIC:  
   could not read file "global/pg_control": read 0 of 296
 stopped waiting
pg_ctl: could not start server
Examine the log output.

设置next-wal-file
-l, –next-wal-file=WALFILE,这个参数设置下一个新的WAL文件的最小值，这个值可以从$PGDATA/pg_wal目录下去看最后一个WAL 文件，这个文件的id+1即可

-bash-4.2$ pwd
/var/lib/pgsql/14/data/pg_wal
-bash-4.2$ ls -l
total 16384
-rw-------. 1 postgres postgres 16777216 May 30 12:04 000000010000000000000014
drwx------. 2 postgres postgres        6 May 24 02:20 archive_status
-bash-4.2$

这个文件+1，-l 000000010000000000000015
设置next-transaction
-x, –next-transaction-id=XID,这个参数设置pg_control中的下一个XID的值，这个值可以从pg_xact目录下的文件中查询

-bash-4.2$ pwd
/var/lib/pgsql/14/data/pg_xact
-bash-4.2$ ls -ltr
total 8
-rw-------. 1 postgres postgres 8192 May 30 12:03 0000

最后一个是0000，那么下一个XID就是0001，然后乘以 1048576 (0×100000)，实际上后面直接加5个0就行了。注意，这个值是16进制的。-x 0×000100000
multixact-ids设置
-m, –multixact-ids=MXID1,MXID2，这个参数包含两个部分，MXID1和MXID2，都可以从$PGDATA/pg_multixact/offsets目录下获得。MXID1的值，首先找到最大值，+1，再乘以 65536 (0×10000，相当于后面加4个0)作为这个参数的前半部分。找到最小的值，后面加4个0，作为MXID2的值

-bash-4.2$ pwd
/var/lib/pgsql/14/data/pg_multixact/offsets
-bash-4.2$ ls -ltr
total 8
-rw-------. 1 postgres postgres 8192 May 29 22:06 0000
-bash-4.2$

-m 0×00010000, 0×00000000（由于oldest multitransaction ID不能为0,因此后续这个值需要适当调整）
multixact-offset设置
-O, –multixact-offset=OFFSET,这个参数可以从$PGDATA/pg_multixact/members目录下获得。找到最大值，+1，乘以 52352 (0xCC80)

-bash-4.2$ pwd
/var/lib/pgsql/14/data/pg_multixact/members
-bash-4.2$ ls -ltr
total 8
-rw-------. 1 postgres postgres 8192 May 24 02:20 0000

-O 0xCC80
尝试执行pg_resetwal 

-bash-4.2$ pg_resetwal -l 000000010000000000000015 -x 0x000100000 -m 0x00010000,0x00000000 -O 0xCC80 $PGDATA
pg_resetwal: error: oldest multitransaction ID (-m) must not be 0

multixact-ids值不对,进行调整后处理
postmaster.pid文件需要清理
由于PG库异常关闭,需要人工清理掉该文件

-bash-4.2$ pg_resetwal -l 000000010000000000000015 -x 0x000100000 -m 0x00020000,0x00010000 -O 0xCC80 $PGDATA
pg_resetwal: error: lock file "postmaster.pid" exists
-bash-4.2$ rm -rf postmaster.pid

pg_resetwal结果预览

-bash-4.2$ pg_resetwal -l 000000010000000000000015 -x 0x000100000 -m 0x00020000,0x00010000 -O 0xCC80 $PGDATA
pg_resetwal: warning: pg_control exists but is broken or wrong version; ignoring it
Guessed pg_control values:

pg_control version number:            1300
Catalog version number:               202107181
Database system identifier:           7103392535324046312
Latest checkpoint's TimeLineID:       1
Latest checkpoint's full_page_writes: off
Latest checkpoint's NextXID:          0:3
Latest checkpoint's NextOID:          12000
Latest checkpoint's NextMultiXactId:  1
Latest checkpoint's NextMultiOffset:  0
Latest checkpoint's oldestXID:        3
Latest checkpoint's oldestXID's DB:   0
Latest checkpoint's oldestActiveXID:  0
Latest checkpoint's oldestMultiXid:   1
Latest checkpoint's oldestMulti's DB: 0
Latest checkpoint's oldestCommitTsXid:0
Latest checkpoint's newestCommitTsXid:0
Maximum data alignment:               8
Database block size:                  8192
Blocks per segment of large relation: 131072
WAL block size:                       8192
Bytes per WAL segment:                16777216
Maximum length of identifiers:        64
Maximum columns in an index:          32
Maximum size of a TOAST chunk:        1996
Size of a large-object chunk:         2048
Date/time type storage:               64-bit integers
Float8 argument passing:              by value
Data page checksum version:           0


Values to be changed:

First log segment after reset:        000000010000000000000015
NextMultiXactId:                      131072
OldestMultiXid:                       65536
OldestMulti's DB:                     0
NextMultiOffset:                      52352
NextXID:                              1048576
OldestXID:                            3
OldestXID's DB:                       0

If these values seem acceptable, use -f to force reset.

pg_resetwal进行创建pg_control并启动PG

-bash-4.2$ pg_resetwal -l 000000010000000000000015 -x 0x000100000 -m 0x00020000,0x00010000 -O 0xCC80 -f $PGDATA
pg_resetwal: warning: pg_control exists but is broken or wrong version; ignoring it
Write-ahead log reset
-bash-4.2$ pg_ctl start
waiting for server to start....2022-05-30 13:33:28.266 CST [51437] LOG:  
redirecting log output to logging collector process
2022-05-30 13:33:28.266 CST [51437] HINT:  Future log output will appear in directory "log".
 done
server started

验证数据

-bash-4.2$ psql
psql (14.3)
Type "help" for help.

postgres=#  select count(1) from ac_event;
 count  
--------
 245275
(1 row)

这种方法恢复之后,建议理解dump数据,然后导入到新库中

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