The document compares synchronous replication solutions for MySQL, specifically focusing on Galera Cluster and MySQL Group Replication. It discusses their histories, features, consistency levels, and support for large transactions, alongside various replication mechanisms and architecture. Key differences include Galera's support for multi-master writes and native GTID, while Group Replication is built on top of GTID with different flow control mechanisms.

1. Wars of MySQL Clusters
(Galera Vs Group Replication)
Karthik P R
CEO, Mydbops
January 30, 2021
Mydbops Database Meetup -8

2. Interested in Open Source Database technologies
11 Years of Experience with MySQL
Ex-Yahoo!
Tech Speaker/ Blogger
CEO Mydbops
Karthik P R
About Me

3. Database
Consulting
Services
Managed
Database
Services
Focuses on Top Opensource database MySQL,MariaDB,
MongoDB and PostgreSQL ON Premises and Cloud
Mydbops Services

4. Replication in MySQL
Synchronous Replication Solutions
History of Synchronous Replication
Galera Vs Group Replication
Features comparison
Agenda

5. Replication in MySQL

6. Replication in MySQL
Replication
Synchronous
Replication
Asynchronous
Replication
Semi Synchronous
Replication

7. Replication in MySQL
Replication ( redundancy ) is a common solution for High Availability
Asynchronous Replication
Native replication ( data lag )
Logical Replication ( Binlog based )
Various architecture is Possible
Filtering in Replication
Engine Independent

8. Replication in MySQL
Synchronous Replication
Zero replication lag
2 Phase commit
Based on Replication Database State Machine Theory
Automated Primary Promotion
Replication is Synchronous
Applying is Asynchronous

9. Synchronous Replication
Solutions

10. Synchronous Replication Solutions
Synchronous
Replication Solutions
Galera Group Replication

11. Synchronous Replication Solutions in MySQL
Synchronous Replication
Galera ( Codership )
Plugin with MySQL
Percona XtraDB Cluster
MariaDB Cluster
Group Replication ( MySQL Native )

12. History of Synchronous
Replication

13. Codership Pioneered the Synchronous replication for MySQL.
Codership released the first version of Galera in May 2007
Percona XtraDB Cluster First release Apr 2012
MariaDB Cluster First release Feb 2014
MySQL Group Replication Dec 2016 ( 5.7.17 )
History of Synchronous Replication

14. Galera Vs Group Replication

15. Supports only InnoDB Engine
Parallel Replication
Multi-master writes
Paxos based
Optimistic locking
Network-based Cluster
Galera & Group Replication

16. Feature Comparison
GCS Protocol
Flow Control
Node Provisioning
Large Transaction Support
Consistency Levels
Galera & Group Replication

17. Feature Comparison
WriteSet Support
WriteSet / Message Cache
Arbitrator Support
Native GTID Support
Load Balancer Support
Galera & Group Replication

18. GSC Protocol

19. Galera Based Solution
Totem Single Ring ordering
Group Replication
Paxos based. eXtended COMmunication ( XCOM )
GCS Protocol

20. Flow Control

21. gcs.fc_limit ,gcs.fc_master_slave, gcs.fc_factor
group_replication_flow_control_mode
Galera Based Solution
Flow Control stops the writes when triggered.
Group Replication
Each node can throttle writes when triggered
Collect stats from every node
Flow Control

22. Node Provisioning

23. Galera Based Solution
IST ( Incremental snapshot transfer )
Incremental state transfer using gcache
SST ( state snapshot transfer )
mysqldump
rsync
xtrabackup-v2 ( Hot method )
Mariabackup ( Hot method in MariaDB Cluster )
Node Provisioning

24. group_replication_clone_threshold auto-provision based on transaction gap.
Group Replication Based Solution
Message cache ( Incremental data )
Async Replication
Clone Plugin - 8.0.17 ( 22-07-2019 )
Node Provisioning

25. Additional Information
https://galeracluster.com/2021/01/galera-cluster-for-mysql-5-6-50-5-7-32-and-8-0-22-released/
Clone Plugin is supported Galera SST from 8.0.22 ( 14 Jan 2021 )
Not available in PXC or MariaDB Cluster yet
Node Provisioning

26. Large Transaction Support

27. Galera Based Solution
Streaming Replication
Galera 4 ( PXC 8.0 and MariaDB 10.4 & above )
wsrep_trx_fragment_size
wsrep_trx_fragment_units
Large Transaction Support

28. The default is 10MB messages above it are fragmented ( chunked ) and
broadcasted.
Group Replication
Huge transaction are supported from 8.0.16 ( 2019-04-25)
group_replication_communication_max_message_size
Large Transaction Support

29. Consistency Level

30. Galera/PXC
The causality check is enabled by "wsrep_sync_wait"
It has multiple levels (0,1,2,3,4,8 )
Consistency Levels

31. Group Replication
The consistency check is controlled by "group_replication_consistency"
It is available from 8.0.14 ( 2019-01-21 )
Modes
EVENTUAL
BEFORE
AFTER
BEFORE AND AFTER
BEFORE_ON_PRIMARY_FAILOVER
Consistency Levels

32. WriteSet Support

33. Galera Based Solution
Galera uses writeset from the initial release with its own GTID
The Parallel replication is enhanced with writeset.
Group Replication
Writeset is introduced on MySQL 8.0
Binlog based transaction extraction applier
Writeset & Writest session ( logical_clock replication )
Writeset Support

34. WriteSet Cache Support

35. Galera Based Solution
Galera uses writeset cache or Gcache for IST and local recovery.
wsrep_provider_option="gcache.size=128M"
Group Replication
It uses message cache size ( From 8.0.16 ) ( 2019-04-25)
Group_replication_message_cache-size ( 128 MB ) 8.0.21
Writeset Cache Support

36. Arbitrator Support

37. * Not a big deal if storage is not a big deal.
Galera Based Solution
Galera Provides Arbitrartor Support
Group Replication
Group Replication does not provide Arbitrator Support
Arbitrator Support

38. Native GTID Support

39. Galera Based Solution
Generates its own GTID in 5.5, 5.6, 5.7 versions
Galera started to support native MySQL GTID from MySQL 8.0.
Group Replication
Group Replication is built on top of GTID
Native GTID Support

40. Load Balancer Support

41. Galera Based Solution
Galera has support for Maxscale and ProxySQL ( inbuilt )
Percona XtraDB Cluster has inbuilt support for ProxySQL
ProxySQL check can be made better with external scripts
Group Replication
Group Replication has support for MySQL Router and ProxySQL
PrxoySQL is most recommended.
Load Balancer Support

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