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MySQL Multi Master Replication


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A presentation by Michael Naumov from Wix that was presented at the MySQL Israel User Group

A presentation by Michael Naumov from Wix that was presented at the MySQL Israel User Group

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  • 1. MySQL Multi-Master Replication Challenge Michael Naumov
  • 2. About Wix 1. We provide a platform to build your own and free awesome web site for any device 2. About 40M Registered Users 3. Around 1.3M new registrations every month 4. About 500 employees with 4 offices around the world.
  • 3. Why do we need Multi-Master topology? The Vision: Multiple, active DBMS servers with exactly the same data 1. Simple high availability model 2. Operate systems over multiple sites 3. Access geographically “close” data
  • 4. BUT! It is not so easy to do as its seems
  • 5. MySQL consistency in stand alone install Transaction #1 Transaction #2 update users update users set follower=10 set follower=100 where id=101 where id=101 Stop
  • 6. Consistency in a Distributed environment Transaction #1 Transaction #2 update users update users set follower=10 set follower=100 where id=101 where id=101
  • 7. Communication latency Transaction #1 In US Transaction #2 in EU Async replication = No application latency SemiSync/Sync replication = Application latency
  • 8. CAP Theorem
  • 9. So what are the solutions out there?
  • 10. MySQL Native Replication
  • 11. How Does Native MySQL M/M Replication Work Master 1 Master 2 Binlog Binlog
  • 12. • Statement replication = send client SQL • Row replication = send changed rows • Use row replication for multi-master Row vs. Statement Replication
  • 13. Auto-Increment Key Offsets • Set different keys on each server to avoid primary key collisions [my.cnf] server-id=1 auto-increment-offset = 1 auto-increment-increment = 4 ... [my.cnf] server-id=2 auto-increment-offset = 2 auto-increment-increment = 4 ...
  • 14. MySQL Multi-Master Topologies Master 1 Master 2 Master 3 Master 2 Master 1 Master-master Circular Replication Replication
  • 15. MySQLNative Replication Summary • Built in with well-known capabilities • MySQL replication by default is asynchronous. In addition to the built-in asynchronous replication, MySQL 5.5 and above supports semi-synchronous replication. • Very limited topology support • Very limited conflict avoidance • Not a good choice for multi-master if there are writes to more than 1 master
  • 16. MySQL Cluster (NDB)
  • 17. How Does NDB Work? Access Layer Storage Layer Mysql Client Mysql Client NDB1 NDB2NDB4 NDB3
  • 18. NDB Eventual Consistency Algorithm • NDB has built-in cross-cluster conflict detection based on epochs and primary keys • Updates to primary always succeed • Update on secondary may be rolled back if primary has a conflicting update • MySQL Cluster resends updates from the primary to “cure” conflicts on the secondary's clusters
  • 19. NDB Supported Topologies NDB Cluster 2 Secondary NDB Cluster 2 Secondary NDB Cluster 3 Secondary NDB Cluster 1 Primary Master-master Circular Replication Replication NDB Cluster 1 Primary
  • 20. MySQLNDB Cluster Summary • Allows active/active operation on 2 clusters • Fully synchronous, no action can be returned to client until transactions on all nodes are really accepted. • NDB is mainly an in memory database and also if it support table on disk the cost of them not always make sense. • Use horizontal partition to equally distribute data cross node, but none of them has the whole dataset • Covers failure of individual MySQL nodes inside the cluster by replication factor • Detects conflicts automatically on rows
  • 21. Galera
  • 22. How Does Galera Work? Galera Replicator Master 1 Master 2 Master 3 wsrep API* wsrep API wsrep API wsrep API (write set replication API), defines the interface between Galera replication and the DBMS
  • 23. Galera approach is Data Centric • Data does not belong to a node – Node belong to data. Using global transaction Id’s • Connect to any nodes for writes • No headache for auto increment. Galera will do it for you • Galera replicate the full dataset across ALL nodes. • Galera replicate data synchronously from one node to cluster on the commit, but apply them on each node by a FIFO queue (multi thread).
  • 24. Galera Summary • Galera require InnoDB to work. • Galera data replication overhead, increase with the number of nodes present in the cluster. • Galera do not offers any parallelism between the nodes when retrieving the data; clients rely on the single node they access. • Synchronous replication • Percona XtraDB Cluster is based on Galera
  • 25. Tungsten
  • 26. How Does Tungsten Replication Work Master Alpha Master Bravo Remote Bravo Slave Tungsten Replicator Alpha Tungsten Replicator Bravo Local Alpha Master Local Bravo Master Remote Alpha Slave
  • 27. Tungsten Failure Handling • Replication stops and resumes automatically when network link goes down • Replication stops on replicator or DBMS failure and recovers after operator restart • Conflicts can break replication. Auto increment keys should be manually configured on each node • Have his own filters for data replication
  • 28. Tungsten Supported Topologies All Masters Star Snowflake
  • 29. Tungsten Summary • Allows active/active operation on N clusters • Transfer is asynchronous • Links can be down for days or weeks if required • It is the application’s responsibility to ensure there are no conflicts • Tungsten Replicator can replicate data from MySQL to MongoDB, Oracle, NuoDB, Vertica and others • Tungsten allows replication from Oracle by using Change Data Capture (CDC). Destination DBMS can be MySQL or Oracle
  • 30. Solution Comparison Native MySQL (5.6) MySQL NDB Galera Tungsten InnoDB + - + + Asynchronous + - + + Statement based + + - + Row Based + - + + Semi-synchronous + - - - Synchronous - + + - Global TRX Id + + + + Time delay replication + - - +
  • 31. Thank you all @NaumovMichael