With its fully integrated solution for MySQL / MariaDB / Percona Server, Tungsten Clustering allows fine control of replica data sources.
- You want to keep a replica read-only.
- Have a node that will never be switched-to and become a primary itself.
- Still want to allow client applications to read data from it.
We call it an "Archive Datasource". It is particularly suitable for hosts that have low computational power and wouldn't hold the write workload.
All you need is to type a single cctrl command:
/alpha > datasource host3 set archive
Managers will never turn an archive datasource into a primary, whereas connectors will still route to it for read-only traffic. More information about selecting a read-only datasource can be found in these blog articles: Selecting the Right Node, Directly From Your Application and Tungsten Cluster: Command Line Superpowers — Easily Control Connector Proxy QoS.
Note that the archive role is a temporary requirement, and will not survive a re-install or upgrade.
- You want a replica to be as up-to-date as possible.
- Prevent the replica from receiving read traffic.
- Have a datasource that is more likely to be selected in case of switch or failover.
That's the “Standby Datasource”. By preventing read traffic, you dedicate computing and networking power to replication, keeping latency as low as possible.
A similar simple command to make that happen:
/alpha > datasource host3 set standby
The connectors will exclude a standby node from their lists of replicas to send traffic to, so it can remain the most up-to-date datasource and more likely to be selected for failover and switch.
Note that the standby role is a temporary requirement, and will not survive a re-install or upgrade.