Every distributed table (except reference tables, which are replicated in whole on each leaf node) has a SHARD KEY that specifies which columns of a row to hash to determine what partition a row should reside in. When rows are inserted into a sharded table, they are hashed by the table’s shard key and sent to the leaf carrying the corresponding partition. This technique is commonly referred to as hash-based partitioning. You can choose how to shard each table by specifying its SHARD KEY as part of the CREATE TABLE statement. See Sharding for more details.
What are aggregator and leaf nodes?
SingleStore Helios stores and computes data on leaf nodes. You can linearly scale both storage and computational power by adding more leaf nodes. Clients query an aggregator node, which in turn queries one or more leaf nodes to collect the rows required to execute the query. Multiple aggregators nodes perform the same functions with respect to executing Data Manipulation Language (DML) queries and allow clients to load-balance queries across the aggregators. Leaf nodes should not be queried directly except for maintenance purposes in exceptional situations.
What is a Master Aggregator?
The Master Aggregator is a specialized aggregator responsible for workspace monitoring and failover.
