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In a MemSQL cluster, an
aggregator is a node that functions as a cluster-aware query router. An aggregator stores only metadata and acts as a gateway into the distributed system. A MemSQL cluster may have one or many aggregators depending on query volume.
An aggregator is responsible for:
- querying the leaves
- aggregating the results
- returning the results to the client
The Master Aggregator is a specialized aggregator responsible for cluster monitoring and failover.
Starting an Aggregator
To add a child aggregator to a MemSQL cluster, pick a node in the cluster that will serve as a child aggregator and append the line
master-aggregator = <master aggregator ip address> to the end its
memsql.cnf. Then start MemSQL using the following command:
$ sudo service memsql start
If you’re running the MemSQL binary directly, start the child aggregator with the following command: