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N:1 Replication meets MHA
This document discusses N:1 replication, which allows multiple master databases to replicate to a single slave database. It describes how N:1 replication works and some limitations, like inability to keep up with schema changes or restarting easily. The document then introduces MHA (Master High Availability), a tool that can automate failover between masters. While N:1 replication and MHA have similar mechanisms for switching masters, N:1 replication requires specifying the exact binlog position, so it does not support automatic failover when a master completely fails like MHA can.
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N:1 Replication meets MHA
- 1. N:1 Replication meets MHA 2014/07/11 MySQLCasual Talks vol6 do_aki
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- 3. About N:1 Replication •Multi Master to Single Slave Replication • a.k.a Multi-source Replication – MariaDB 10 (https://mariadb.com/kb/en/mariadb/mariadb- documentation/replication-cluster-multi-master/replication/multi- source-replication/) – MySQL 5.7 (labs) (http://www.mysqlperformanceblog.com/2013/10/02/mysql-5-7-multi- source-replication/) • N:1 Replication work on MySQL5.0!
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- 5. Master A Slave A+B Master B CHANGE MATER TO ‘Master A’ repeatfor ever per 2seconds
- 6. Master A Slave A+B Master B CHANGE MATER TO ‘Master B’ repeatfor ever per 2seconds
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- 10. Flowchart of N:1Replication wait for Seconds_Behind_Master = 0 START SLAVE STOP SLAVE IO_THREAD MASTER_POS_WAIT(Master_Log_F ile,Read_Master_Log_Pos) Timeout? START SLAVE IO_THREAD STOP SLAVE CHANGE MASTER TO ‘next master’ Yes No
- 11. I talked aboutabove at 3 years ago
- 12. Current N:1 Replication •Work in my production for 3 years • I almost never use time to maintenance • can’t keep pace in some case – pt-online-schema-change – master server changed – need restart (relatively trouble)
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- 14. temporary rotation stop •n1repl_command.pl stop – stop rotate replication connection – single replication is alive • n1repl_command.pl start – start rotate replication connection
- 15. support changed masterserver n1repl_command.pl switch --orig_master_host = masterA --orig_master_port = 3306 --orig_master_log_file = bin.00x --orig_master_log_pos = 893 --new_master_host = masterB --new_master_pos = 3306 --new_master_log_file = bin.00x --new_master_log_pos = 1129
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- 19. MHA for MySQL •Master High Availability Manager and tools for MySQL (https://code.google.com/p/mysql-master-ha/) • Automating master failover – slave promotes to master when master goes down – include “Graceful master switch” function (masterha_master_switch --master_state=alive) http://www.slideshare.net/matsunobu/automated-master-failover/44
- 20. MHA (master switch)1 current master (orig_master) other slaves candidate of master (new_master) write
- 21. MHA (master switch)2 write record binlog filename and position (orig_master_log_file, orig_master_log_pos)
- 22. MHA (master switch)3 MASTER_POS_WAIT( orig_master_log_file, orig_master_log_pos) record binlog (new_master_log_file, new_master_log_pos) write
- 23. MHA (master switch)4 other slaves: MASTER_POS_WAIT( orig_master_log_file, orig_master_log_pos) CHANGE MASTER TO ‘new_master’ (new_master_log_file, new_master_log_pos) write write
- 24. MHA (master switch)5 write complete!
- 25. similar mechanism • waitreplication delay is zero • change connection • specify same (orig->new) position • it’s looked N:1 Replication code
- 26. support changed masterserver n1repl_command.pl switch --orig_master_host = masterA --orig_master_port = 3306 --orig_master_log_file = bin.00x --orig_master_log_pos = 893 --new_master_host = masterB --new_master_pos = 3306 --new_master_log_file = bin.00x --new_master_log_pos = 1129
- 27. But but but... •Don’t work when master is dead • MHA has hook functions call specified script *without* binlog file and position!
- 28. Conclusion • N:1 Replicationnot support MHA… • please expect “JIKAISAKU”
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