Citus vs Greenplum Database: What are the differences?

Key Differences between Citus and Greenplum Database

Citus and Greenplum Database are both distributed databases that provide scalability and high-performance for handling large volumes of data. However, there are several key differences between these two databases.

1. Architecture: Citus is built on top of PostgreSQL and extends it with a distributed architecture that allows it to horizontally scale across multiple nodes. On the other hand, Greenplum Database is based on the PostgreSQL project but includes a parallel query engine that enables it to process large datasets in a distributed manner.

2. Data Distribution: Citus uses sharding to distribute data across multiple nodes in a cluster. It partitions the data based on a configurable shard key, allowing queries to be executed in parallel on different shards. In contrast, Greenplum Database uses a concept called the "interleaved sort key" to distribute data across segments. This allows for efficient data retrieval as segments can be accessed in parallel.

3. Query Execution: Citus leverages query-aware sharding to optimize query execution. It pushes down certain operations to individual shards and performs query coordination at the coordinator node, reducing data movement and improving performance. Greenplum Database, on the other hand, employs a massively parallel processing (MPP) approach where queries are divided into smaller tasks that are executed in parallel across segments.

4. Workload Management: Citus provides automatic workload management that dynamically adjusts the number of shards a query runs on based on available resources. This ensures that queries are efficiently distributed and utilize the cluster's resources optimally. Greenplum Database also offers workload management capabilities through its Query Resource Manager (QRM) that allows administrators to allocate system resources to different queries and users.

5. Data Types: Citus supports most of the PostgreSQL data types and extensions, making it compatible with existing applications. Greenplum Database, on the other hand, has its own set of data types and functions, which may require some modifications to existing applications when migrating.

6. Community and Support: Citus is an open-source extension to PostgreSQL and benefits from the vibrant PostgreSQL community. It also offers enterprise support through a paid subscription. Greenplum Database is a commercially-supported product with a dedicated support team from the parent company.

In Summary, while both Citus and Greenplum Database are distributed databases that provide scalability and high-performance, they differ in terms of architecture, data distribution, query execution, workload management, data types, and community and support.