Quick Review: Mysql NDB cluster

 This is a quick 2 min overview of Mysql NDB Cluster. The goal is to help you decide within a minute or two, whether this is an appropriate solution for you.

Cluster of in-memory Mysql databases with a shared nothing architecture.

Consists of Mysql nodes and data nodes.

Mysql nodes are Mysql servers that get data from data nodes. Data nodes hold the data using the NDB storage engine. There are also admin nodes.

NDB nodes serve the data from memory. Data is persisted at checkpoints.

Data is partitioned and replicated.

Up to 48 data nodes and 2 replicas for each fragment of data.

ACID compliant.

READ_COMMITTED  isolation level.

Sharding of data is done automatically. No involvement of user or application is required.

Data is replicated for high availability. Node failures are handled automatically.

Clients can access data using NDB Api. Both SQL and NOSQL styles are possible.

This is not a good general purpose database. It is suitable for certain specific use cases of telecom and game but not for general OLTP.

Feels like it has too many moving parts to manage.

High performance -- it is serving data from memory.

Summary

Not a general purpose distributed databases. Unless you are in telecom or gaming or know for sure why this meets your use case, don'nt even think about it.

If you are on Mysql and want high availability, try Mysql InnoDb Cluster, which is much easier to understand and use.

Quick Review: Mysql InnoDb Cluster

 

This is a quick 2 min overview of Mysql InnoDb Cluster. The goal is to help you decide within a minute or two, whether this is an appropriate solution for you.

Simple HA solution for Mysql.

Built on top of MySql group replication.

It has 3 Components:

Replication: Uses existing mysql asynchronous replication capabilities. Default is Primary and secondary configuration. Writes go to master which replicates to slaves. Slaves can service reads

Mysql router: Provides routing between your application and the cluster. Supports automatic failover. If the primary dies. The router will redirect writes to the secondary that takes over.

Mysql shell: This is an advance shell that let you code and configure the cluster.

Works best over a local area network. Performance degrades over wide area networks

Easy to setup. Simple commands that are entered on the mysql shell. 

var cluster = dba.createCluster('testCluster')

cluster.addInstance('server1@host1:3306')

cluster.addInstance('server2@host2:3306')

cluster.addInstance('server3@host3:3306')

Cluster elects the primary. If you want a particular server to be the primary, you can give it extra weight.

Client do not connect directly to the servers. Rather they connect to the Mysql router that provides the routing as well failover.

MySql InnoDB clusterSet provide additional resiliency by replicating data from a primary cluster to a cluster in another datacenter or location. If the primary cluster becomes available, one of the secondary cluster can become the primary.

Summary

Provides scalability for reads and some HA for Mysql deployments. Simple, easy to use solution. No sharding. Some consistency issues will there when you read from replicas that lag a little bit

References:

https://dev.mysql.com/doc/mysql-shell/8.0/en/mysql-innodb-cluster.html