Interaction of Cluster Components
You run database queries against an aggregator. Most of the communication between aggregators and leaves for query execution is also implemented as SQL statements.
Parallel Execution of Queries
By default, SingleStoreDB will create one partition per CPU core on the leaves for maximum parallelism. This number is configurable cluster-wide with the default-partitions-per-leaf variable, or as an optional parameter to CREATE DATABASE.
In the context of query execution, a partition is the granular unit of query parallelism. In other words, every parallel query is run with a level of parallelism equal to the number of partitions. You can view the partitions in a database with SHOW PARTITIONS.