数据库内核月报 - 2019 / 02

PgSQL · 应用案例 · PostgreSQL 时间线修复

背景

1、PG物理流复制的从库,当激活后,可以开启读写,使用pg_rewind可以将从库回退为只读从库的角色。而不需要重建整个从库。

2、当异步主从发生角色切换后,主库的wal目录中可能还有没完全同步到从库的内容,因此老的主库无法直接切换为新主库的从库。使用pg_rewind可以修复老的主库,使之成为新主库的只读从库。而不需要重建整个从库。

3、如果没有pg_rewind,遇到以上情况,需要完全重建从库。或者你可以使用存储层快照,回退回脑裂以前的状态。又或者可以使用文件系统快照,回退回脑裂以前的状态。

原理与修复步骤

1、使用pg_rewind功能的前提条件:必须开启full page write,必须开启wal hint或者data block checksum。

2、需要被修复的库:从激活点开始,所有的WAL必须存在pg_wal目录中。如果WAL已经被覆盖,只要有归档,拷贝到pg_wal目录即可。

3、新的主库,从激活点开始,产生的所有WAL必须存在pg_wal目录中,或者已归档,并且被修复的库可以使用restore_command访问到这部分WAL。

4、修改(source db)新主库或老主库配置,允许连接。

5、修复时,连接新主库,得到切换点。或连接老主库,同时比对当前要修复的新主库的TL与老主库进行比对,得到切换点。

6、解析需要被修复的库的从切换点到现在所有的WAL。同时连接source db(新主库(或老主库)),进行回退操作(被修改或删除的BLOCK从source db获取并覆盖,新增的BLOCK,直接抹除。)回退到切换点的状态。

7、修改被修复库(target db)的recovery.conf, postgresql.conf配置。

8、启动target db,连接source db接收WAL,或restore_command配置接收WAL,从切换点开始所有WAL,进行apply。

9、target db现在是source db的从库。

以EDB PG 11为例讲解

环境部署

《MTK使用 - PG,PPAS,oracle,mysql,ms sql,sybase 迁移到 PG, PPAS (支持跨版本升级)》

export PS1="$USER@`/bin/hostname -s`-> "      
export PGPORT=4000  
export PGDATA=/data04/ppas11/pg_root4000  
export LANG=en_US.utf8      
export PGHOME=/usr/edb/as11  
export LD_LIBRARY_PATH=$PGHOME/lib:/lib64:/usr/lib64:/usr/local/lib64:/lib:/usr/lib:/usr/local/lib:$LD_LIBRARY_PATH      
export DATE=`date +"%Y%m%d%H%M"`    
export PATH=$PGHOME/bin:$PATH:.      
export MANPATH=$PGHOME/share/man:$MANPATH      
export PGHOST=127.0.0.1  
export PGUSER=postgres   
export PGDATABASE=postgres      
alias rm='rm -i'      
alias ll='ls -lh'      
unalias vi    

1、初始化数据库集群

initdb -D /data04/ppas11/pg_root4000 -E UTF8 --lc-collate=C --lc-ctype=en_US.UTF8 -U postgres -k --redwood-like   

2、配置recovery.done

cd $PGDATA  
  
cp $PGHOME/share/recovery.conf.sample ./  
  
mv recovery.conf.sample recovery.done  
  
vi recovery.done  
  
restore_command = 'cp /data04/ppas11/wal/%f %p'  
recovery_target_timeline = 'latest'  
standby_mode = on  
primary_conninfo = 'host=localhost port=4000 user=postgres'  

3、配置postgresql.conf

要使用rewind功能:

必须开启full_page_writes

必须开启data_checksums或wal_log_hints

postgresql.conf  
  
listen_addresses = '0.0.0.0'  
port = 4000  
max_connections = 8000  
superuser_reserved_connections = 13  
unix_socket_directories = '.,/tmp'  
unix_socket_permissions = 0700  
tcp_keepalives_idle = 60  
tcp_keepalives_interval = 10  
tcp_keepalives_count = 10  
shared_buffers = 16GB  
max_prepared_transactions = 8000  
maintenance_work_mem = 1GB  
autovacuum_work_mem = 1GB  
dynamic_shared_memory_type = posix  
vacuum_cost_delay = 0  
bgwriter_delay = 10ms  
bgwriter_lru_maxpages = 1000  
bgwriter_lru_multiplier = 10.0  
effective_io_concurrency = 0  
max_worker_processes = 128  
max_parallel_maintenance_workers = 8  
max_parallel_workers_per_gather = 8  
max_parallel_workers = 24  
wal_level = replica  
synchronous_commit = off  
full_page_writes = on  
wal_compression = on  
wal_buffers = 32MB  
wal_writer_delay = 10ms  
checkpoint_timeout = 25min  
max_wal_size = 32GB  
min_wal_size = 8GB  
checkpoint_completion_target = 0.2  
archive_mode = on  
archive_command = 'cp -n %p /data04/ppas11/wal/%f'  
max_wal_senders = 16  
wal_keep_segments = 4096  
max_replication_slots = 16  
hot_standby = on  
max_standby_archive_delay = 300s  
max_standby_streaming_delay = 300s  
wal_receiver_status_interval = 1s  
wal_receiver_timeout = 10s  
random_page_cost = 1.1  
effective_cache_size = 400GB  
log_destination = 'csvlog'  
logging_collector = on  
log_directory = 'log'  
log_filename = 'edb-%a.log'  
log_truncate_on_rotation = on  
log_rotation_age = 1d  
log_rotation_size = 0  
log_min_duration_statement = 1s  
log_checkpoints = on  
log_error_verbosity = verbose  
log_line_prefix = '%t '  
log_lock_waits = on  
log_statement = 'ddl'  
log_timezone = 'PRC'  
autovacuum = on  
log_autovacuum_min_duration = 0  
autovacuum_max_workers = 6  
autovacuum_freeze_max_age = 1200000000  
autovacuum_multixact_freeze_max_age = 1400000000  
autovacuum_vacuum_cost_delay = 0  
statement_timeout = 0  
lock_timeout = 0  
idle_in_transaction_session_timeout = 0  
vacuum_freeze_table_age = 1150000000  
vacuum_multixact_freeze_table_age = 1150000000  
datestyle = 'redwood,show_time'  
timezone = 'PRC'  
lc_messages = 'en_US.utf8'  
lc_monetary = 'en_US.utf8'  
lc_numeric = 'en_US.utf8'  
lc_time = 'en_US.utf8'  
default_text_search_config = 'pg_catalog.english'  
shared_preload_libraries = 'auto_explain,pg_stat_statements,$libdir/dbms_pipe,$libdir/edb_gen,$libdir/dbms_aq'  
edb_redwood_date = on  
edb_redwood_greatest_least = on  
edb_redwood_strings = on  
db_dialect = 'redwood'                
edb_dynatune = 66  
edb_dynatune_profile = oltp  
timed_statistics = off  

4、配置pg_hba.conf,允许流复制

local   all             all                                     trust  
host    all             all             127.0.0.1/32            trust  
host    all             all             ::1/128                 trust  
local   replication     all                                     trust  
host    replication     all             127.0.0.1/32            trust  
host    replication     all             ::1/128                 trust  
host all all 0.0.0.0/0 md5  

5、配置归档目录

mkdir /data04/ppas11/wal    
chown enterprisedb:enterprisedb /data04/ppas11/wal  

6、创建从库

pg_basebackup -h 127.0.0.1 -p 4000 -D /data04/ppas11/pg_root4001 -F p -c fast  

7、配置从库

cd /data04/ppas11/pg_root4001  
  
mv recovery.done recovery.conf  
vi postgresql.conf  
  
port = 4001  

8、启动从库

pg_ctl start -D /data04/ppas11/pg_root4001  

9、压测主库

pgbench -i -s 1000  
  
pgbench -M prepared -v -r -P 1 -c 24 -j 24 -T 300  

10、检查归档

postgres=# select * from pg_stat_archiver ;  
 archived_count |    last_archived_wal     |        last_archived_time        | failed_count | last_failed_wal | last_failed_time |           stats_reset              
----------------+--------------------------+----------------------------------+--------------+-----------------+------------------+----------------------------------  
            240 | 0000000100000000000000F0 | 28-JAN-19 15:08:43.276965 +08:00 |            0 |                 |                  | 28-JAN-19 15:01:17.883338 +08:00  
(1 row)  
  
postgres=# select * from pg_stat_archiver ;  
 archived_count |    last_archived_wal     |        last_archived_time        | failed_count | last_failed_wal | last_failed_time |           stats_reset              
----------------+--------------------------+----------------------------------+--------------+-----------------+------------------+----------------------------------  
            248 | 0000000100000000000000F8 | 28-JAN-19 15:08:45.120134 +08:00 |            0 |                 |                  | 28-JAN-19 15:01:17.883338 +08:00  
(1 row)  

11、检查从库延迟

postgres=# select * from pg_stat_replication ;  
-[ RECORD 1 ]----+---------------------------------  
pid              | 8124  
usesysid         | 10  
usename          | postgres  
application_name | walreceiver  
client_addr      | 127.0.0.1  
client_hostname  |   
client_port      | 62988  
backend_start    | 28-JAN-19 15:07:34.084542 +08:00  
backend_xmin     |   
state            | streaming  
sent_lsn         | 1/88BC2000  
write_lsn        | 1/88BC2000  
flush_lsn        | 1/88BC2000  
replay_lsn       | 1/88077D48  
write_lag        | 00:00:00.001417  
flush_lag        | 00:00:00.002221  
replay_lag       | 00:00:00.097657  
sync_priority    | 0  
sync_state       | async  

例子1,从库激活后产生读写,使用pg_rewind修复从库,回退到只读从库

1、激活从库

pg_ctl promote -D /data04/ppas11/pg_root4001  

2、写从库

pgbench -M prepared -v -r -P 1 -c 4 -j 4 -T 120 -p 4001  

此时从库已经和主库不在一个时间线,无法直接变成当前主库的从库

enterprisedb@pg11-test-> pg_controldata -D /data04/ppas11/pg_root4001|grep -i time  
Latest checkpoint's TimeLineID:       1  
Latest checkpoint's PrevTimeLineID:   1  
Time of latest checkpoint:            Mon 28 Jan 2019 03:56:38 PM CST  
Min recovery ending loc's timeline:   2  
track_commit_timestamp setting:       off  
Date/time type storage:               64-bit integers  
  
enterprisedb@pg11-test-> pg_controldata -D /data04/ppas11/pg_root4000|grep -i time  
Latest checkpoint's TimeLineID:       1  
Latest checkpoint's PrevTimeLineID:   1  
Time of latest checkpoint:            Mon 28 Jan 2019 05:11:38 PM CST  
Min recovery ending loc's timeline:   0  
track_commit_timestamp setting:       off  
Date/time type storage:               64-bit integers  

3、修复从库,使之继续成为当前主库的从库

4、查看切换点

cd /data04/ppas11/pg_root4001  
  
ll pg_wal/*.history  
-rw------- 1 enterprisedb enterprisedb 42 Jan 28 17:15 pg_wal/00000002.history  
  
cat pg_wal/00000002.history  
1       6/48C62000      no recovery target specified  

5、从库激活时间开始产生的WAL必须全部在pg_wal目录中。

-rw------- 1 enterprisedb enterprisedb   42 Jan 28 17:15 00000002.history  
-rw------- 1 enterprisedb enterprisedb  16M Jan 28 17:16 000000020000000600000048  
............  

000000020000000600000048开始,所有的wal必须存在从库pg_wal目录中。如果已经覆盖了,必须从归档目录拷贝到从库pg_wal目录中。

6、从库激活时,主库从这个时间点开始所有的WAL还在pg_wal目录,或者从库可以使用restore_command获得(recovery.conf)。

recovery.conf  
  
restore_command = 'cp /data04/ppas11/wal/%f %p'  

7、pg_rewind命令帮助

https://www.postgresql.org/docs/11/app-pgrewind.html

pg_rewind --help  
pg_rewind resynchronizes a PostgreSQL cluster with another copy of the cluster.  
  
Usage:  
  pg_rewind [OPTION]...  
  
Options:  
  -D, --target-pgdata=DIRECTORY  existing data directory to modify  
      --source-pgdata=DIRECTORY  source data directory to synchronize with  
      --source-server=CONNSTR    source server to synchronize with  
  -n, --dry-run                  stop before modifying anything  
  -P, --progress                 write progress messages  
      --debug                    write a lot of debug messages  
  -V, --version                  output version information, then exit  
  -?, --help                     show this help, then exit  
  
Report bugs to <support@enterprisedb.com>.  

8、停库(被修复的库,停库)

pg_ctl stop -m fast -D /data04/ppas11/pg_root4001  

9、尝试修复

pg_rewind -n -D /data04/ppas11/pg_root4001 --source-server="hostaddr=127.0.0.1 user=postgres port=4000"  
  
servers diverged at WAL location 6/48C62000 on timeline 1  
rewinding from last common checkpoint at 5/5A8CD30 on timeline 1  
Done!  

10、尝试正常,说明可以修复,实施修复

pg_rewind -D /data04/ppas11/pg_root4001 --source-server="hostaddr=127.0.0.1 user=postgres port=4000"  
  
servers diverged at WAL location 6/48C62000 on timeline 1  
rewinding from last common checkpoint at 5/5A8CD30 on timeline 1  
Done!  

11、已修复,改配置

cd /data04/ppas11/pg_root4001  
  
vi postgresql.conf  
port = 4001  
mv recovery.done recovery.conf  
  
vi recovery.conf  
  
restore_command = 'cp /data04/ppas11/wal/%f %p'   
recovery_target_timeline = 'latest'   
standby_mode = on   
primary_conninfo = 'host=localhost port=4000 user=postgres'   

12、删除归档中错误时间线上产生的文件否则会在启动修复后的从库后,走到00000002时间线上,这是不想看到的。

mkdir /data04/ppas11/wal/error_tl_2  
  
mv /data04/ppas11/wal/00000002* /data04/ppas11/wal/error_tl_2  

13、启动从库

pg_ctl start -D /data04/ppas11/pg_root4001  

14、建议对主库做一个检查点,从库收到检查点后,重启后不需要应用太多WAL,而是从新检查点开始恢复

psql  
checkpoint;  

15、压测主库

pgbench -M prepared -v -r -P 1 -c 16 -j 16 -T 200 -p 4000  

16、查看归档状态

postgres=# select * from pg_stat_archiver ;  
 archived_count |    last_archived_wal     |        last_archived_time        | failed_count | last_failed_wal | last_failed_time |           stats_reset              
----------------+--------------------------+----------------------------------+--------------+-----------------+------------------+----------------------------------  
           1756 | 0000000100000006000000DC | 28-JAN-19 17:41:57.562425 +08:00 |            0 |                 |                  | 28-JAN-19 15:01:17.883338 +08:00  
(1 row)  

17、查看从库健康、延迟,观察修复后的情况

postgres=# select * from pg_stat_replication ;  
-[ RECORD 1 ]----+--------------------------------  
pid              | 13179  
usesysid         | 10  
usename          | postgres  
application_name | walreceiver  
client_addr      | 127.0.0.1  
client_hostname  |   
client_port      | 63198  
backend_start    | 28-JAN-19 17:47:29.85308 +08:00  
backend_xmin     |   
state            | catchup  
sent_lsn         | 7/DDE80000  
write_lsn        | 7/DC000000  
flush_lsn        | 7/DC000000  
replay_lsn       | 7/26A8DCB0  
write_lag        | 00:00:18.373263  
flush_lag        | 00:00:18.373263  
replay_lag       | 00:00:18.373263  
sync_priority    | 0  
sync_state       | async  

例子2,从库激活成为新主库后,老主库依旧有读写,使用pg_rewind修复老主库,将老主库降级为新主库的从库

1、激活从库

pg_ctl promote -D /data04/ppas11/pg_root4001  

2、写从库

pgbench -M prepared -v -r -P 1 -c 16 -j 16 -T 200 -p 4001  

3、写主库

pgbench -M prepared -v -r -P 1 -c 16 -j 16 -T 200 -p 4000  

此时老主库已经和新的主库不在一个时间线

enterprisedb@pg11-test-> pg_controldata -D /data04/ppas11/pg_root4000|grep -i timeline  
Latest checkpoint's TimeLineID:       1  
Latest checkpoint's PrevTimeLineID:   1  
Min recovery ending loc's timeline:   0  
enterprisedb@pg11-test-> pg_controldata -D /data04/ppas11/pg_root4001|grep -i timeline  
Latest checkpoint's TimeLineID:       1  
Latest checkpoint's PrevTimeLineID:   1  
Min recovery ending loc's timeline:   2  
  
  
enterprisedb@pg11-test-> cd /data04/ppas11/pg_root4001/pg_wal  
enterprisedb@pg11-test-> cat 00000002.history   
1       8/48DE2318      no recovery target specified  
  
enterprisedb@pg11-test-> ll *.partial  
-rw------- 1 enterprisedb enterprisedb 16M Jan 28 17:48 000000010000000800000048.partial  

4、修复老主库,变成从库

4.1、从库激活时,老主库从这个时间点开始所有的WAL,必须全部在pg_wal目录中。

000000010000000800000048 开始的所有WAL必须存在pg_wal,如果已经覆盖了,必须从WAL归档拷贝到pg_wal目录

4.2、从库激活时间开始产生的所有WAL,老主库必须可以使用restore_command获得(recovery.conf)。

recovery.conf  
  
restore_command = 'cp /data04/ppas11/wal/%f %p'  

5、关闭老主库

pg_ctl stop -m fast -D /data04/ppas11/pg_root4000  

6、尝试修复老主库

pg_rewind -n -D /data04/ppas11/pg_root4000 --source-server="hostaddr=127.0.0.1 user=postgres port=4001"  
  
servers diverged at WAL location 8/48DE2318 on timeline 1  
rewinding from last common checkpoint at 6/CCCEF770 on timeline 1  
Done!  

7、尝试成功,可以修复,实施修复

pg_rewind -D /data04/ppas11/pg_root4000 --source-server="hostaddr=127.0.0.1 user=postgres port=4001"  

8、修复完成后,改配置

cd /data04/ppas11/pg_root4000  
  
vi postgresql.conf  
port = 4000  
mv recovery.done recovery.conf  
  
vi recovery.conf  
  
restore_command = 'cp /data04/ppas11/wal/%f %p'   
recovery_target_timeline = 'latest'   
standby_mode = on   
primary_conninfo = 'host=localhost port=4001 user=postgres'    

9、启动老主库

pg_ctl start -D /data04/ppas11/pg_root4000  

10、建议对新主库做一个检查点,从库收到检查点后,重启后不需要应用太多WAL,而是从新检查点开始恢复

checkpoint;  

11、压测新主库

pgbench -M prepared -v -r -P 1 -c 16 -j 16 -T 200 -p 4001  

12、查看归档状态

psql -p 4001  
  
  
postgres=# select * from pg_stat_archiver ;  
 archived_count |    last_archived_wal     |        last_archived_time        | failed_count | last_failed_wal | last_failed_time |           stats_reset              
----------------+--------------------------+----------------------------------+--------------+-----------------+------------------+----------------------------------  
            406 | 0000000200000009000000DB | 28-JAN-19 21:18:22.976118 +08:00 |            0 |                 |                  | 28-JAN-19 17:47:29.847488 +08:00  
(1 row)  

13、查看从库健康、延迟

psql -p 4001  
  
postgres=# select * from pg_stat_replication ;  
-[ RECORD 1 ]----+---------------------------------  
pid              | 17675  
usesysid         | 10  
usename          | postgres  
application_name | walreceiver  
client_addr      | 127.0.0.1  
client_hostname  |   
client_port      | 60530  
backend_start    | 28-JAN-19 21:18:36.472197 +08:00  
backend_xmin     |   
state            | streaming  
sent_lsn         | 9/E8361C18  
write_lsn        | 9/E8361C18  
flush_lsn        | 9/E8361C18  
replay_lsn       | 9/D235B520  
write_lag        | 00:00:00.000101  
flush_lag        | 00:00:00.000184  
replay_lag       | 00:00:03.028098  
sync_priority    | 0  
sync_state       | async  

小结

1 适合场景

1、PG物理流复制的从库,当激活后,可以开启读写,使用pg_rewind可以将从库回退为只读从库的角色。而不需要重建整个从库。

2、当异步主从发生角色切换后,主库的wal目录中可能还有没完全同步到从库的内容,因此老的主库无法直接切换为新主库的从库。使用pg_rewind可以修复老的主库,使之成为新主库的只读从库。而不需要重建整个从库。

如果没有pg_rewind,遇到以上情况,需要完全重建从库,如果库占用空间很大,重建非常耗时,也非常耗费上游数据库的资源(读)。

2 前提

要使用rewind功能:

1、必须开启full_page_writes

2、必须开启data_checksums或wal_log_hints

initdb -k 开启data_checksums  

3 原理与修复流程

1、使用pg_rewind功能的前提条件:必须开启full page write,必须开启wal hint或者data block checksum。

2、需要被修复的库:从激活点开始,所有的WAL必须存在pg_wal目录中。如果WAL已经被覆盖,只要有归档,拷贝到pg_wal目录即可。

3、新的主库,从激活点开始,产生的所有WAL必须存在pg_wal目录中,或者已归档,并且被修复的库可以使用restore_command访问到这部分WAL。

4、修改(source db)新主库或老主库配置,允许连接。

5、修复时,连接新主库,得到切换点。或连接老主库,同时比对当前要修复的新主库的TL与老主库进行比对,得到切换点。

6、解析需要被修复的库的从切换点到现在所有的WAL。同时连接source db(新主库(或老主库)),进行回退操作(被修改或删除的BLOCK从source db获取并覆盖,新增的BLOCK,直接抹除。)回退到切换点的状态。

7、修改被修复库(target db)的recovery.conf, postgresql.conf配置。

8、启动target db,连接source db接收WAL,或restore_command配置接收WAL,从切换点开始所有WAL,进行apply。

9、target db现在是source db的从库。

参考

https://www.postgresql.org/docs/11/app-pgrewind.html

《PostgreSQL primary-standby failback tools : pg_rewind》

《PostgreSQL 9.5 new feature - pg_rewind fast sync Split Brain Primary & Standby》

《PostgreSQL 9.5 add pg_rewind for Fast align for PostgreSQL unaligned primary & standby》

《MTK使用 - PG,PPAS,oracle,mysql,ms sql,sybase 迁移到 PG, PPAS (支持跨版本升级)》

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