Table Engine

The MergeTree engine and other engines of the MergeTree family (e.g. ReplacingMergeTree, AggregatingMergeTree ) are the most commonly used and most robust table engines in ClickHouse.

Main features of MergeTree family table engines.

• The primary key does not reference individual rows but blocks of 8192 rows called granules. This makes primary keys of huge data sets small enough to remain loaded in main memory, while still providing fast access to on-disk data.

MergeTree

The most versatile and commonly used table engine that stores data in parts sorted by primary key and supports efficient range queries, updates, and deletions.

SummingMergeTree

Automatically sums numeric columns with the same primary key during background merges, making it ideal for storing pre-aggregated data like metrics and counters.

ReplacingMergeTree

Removes duplicate rows with the same primary key during merges, keeping only the latest version based on an optional version column for data deduplication.

AggregatingMergeTree

Stores intermediate aggregation states and merges them using aggregate functions during background operations, perfect for building materialized views with complex aggregations.