The following key concepts are necessary for understanding how to administer a MemSQL environment.

• Databases
• Tables
• Queries
• Master Aggregator
• Aggregators
• Leaves

MemSQL’s distributed architecture provides commands and settings used to manage a MemSQL cluster.

Cluster Administration Commands

• ADD LEAF
• REMOVE LEAF
• ATTACH LEAF
• DETACH LEAF
• SHOW LEAVES
• ADD AGGREGATOR
• REMOVE AGGREGATOR
• BOOTSTRAP AGGREGATOR
• REBALANCE PARTITIONS
• EXPLAIN REBALANCE PARTITIONS
• SHOW REBALANCE STATUS
• SHOW PARTITIONS

Setting the Redundancy Level

To use Availability Groups in a cluster, you need to set the redundancy level, which specifies the maximum number (1 or 2) of availability groups. By default, this is set to 1. There are two ways in which to change the redundancy level.

Setting the Engine Variable

One way is to use the SET GLOBAL command to change redundancy_level engine variable on the master aggregator at runtime (see Setting the Redundancy Level):

memsql> SET @@GLOBAL.redundancy_level = {1 | 2};

You can inspect the current value with the SELECT GLOBAL command:

memsql> SELECT @@GLOBAL.redundancy_level;

Adding and Removing Leaves

Use ADD LEAF and REMOVE LEAF to add leaves to, and remove leaves from, a MemSQL cluster.

Adding and Removing Child Aggregators

Use ADD AGGREGATOR and REMOVE AGGREGATOR to add and remove child aggregators from a MemSQL cluster.

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