Question: What is sharding in PostgreSQL?


Sharding is a method of distributing data across multiple servers or databases to improve the performance and scalability of a database system. In the context of PostgreSQL, a popular open-source relational database, sharding involves partitioning large databases into smaller, more manageable pieces known as 'shards'. Each shard contains a subset of the total dataset and can be stored on separate database servers. This approach allows for horizontal scaling, as you can add more servers to handle increased load.

Why Use Sharding?

  • Scalability: As data grows, it becomes challenging to manage it on a single server. Sharding makes it easier to scale your database horizontally by adding more shards/servers.
  • Performance: Queries can run faster as they operate on less data at a time. Also, read/write loads are distributed across multiple servers, reducing contention.
  • High Availability: By replicating shards across servers, you can ensure that the failure of one server doesn’t mean the loss of all data.

How to Implement Sharding in PostgreSQL?

PostgreSQL does not provide built-in automatic sharding capabilities. However, there are several ways to implement sharding:

1. Manual Sharding

You manually split your data into shards and distribute them across different PostgreSQL instances. Your application logic needs to know which shard to query for the data it needs.

2. PostgreSQL Foreign Data Wrappers (FDW)

FDWs allow PostgreSQL servers to communicate with external data sources like other SQL databases, NoSQL databases, or even files. You can create a foreign table in a PostgreSQL database that represents a shard stored in another PostgreSQL instance.

3. Extensions Like Citus

Citus is an open-source extension for PostgreSQL that turns it into a distributed database system, enabling easy sharding and replication. It automatically distributes your data and queries across multiple nodes.

-- Example of creating a distributed table with Citus SELECT create_distributed_table('table_name', 'distribution_column');

This command tells Citus to shard the specified table by the distribution column, distributing the rows across different nodes based on the values of that column.


While PostgreSQL does not offer out-of-the-box sharding, various methods, including third-party extensions like Citus, enable effective sharding strategies. Choosing the right approach depends on your specific requirements, including the size of your dataset, your performance goals, and your willingness to manage complexity.

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