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
• 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 System Variable

One way is to use the SET GLOBAL command to change redundancy_level system 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 redundancy_level to memsql.cnf

Another way is to add the redundancy_level setting anywhere in the memsql.cnf file (see memsql.cnf Settings). There are two settings:

redundancy_level=1 (default) - no redundancy redundancy_level=2 - to allow up to two availability groups

Adding and Removing Leaves

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

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