Sharded In-Memory Store

Sharding is a technique used to distribute data across multiple storage backends, improving performance and scalability by evenly spreading the load. In the context of Stalwart Mail Server's sharded in-memory store, sharding works by hashing the key of the data to be stored or retrieved and using a modulus operation to determine which in-memory store should handle the request. This ensures that each backend is responsible for a specific subset of the keys, enabling efficient use of resources and preventing bottlenecks.

Enterprise feature

This feature is available exclusively in the Enterprise Edition of Stalwart Mail Server and not included in the Community Edition.

Configuration

Configuring a sharded in-memory store in Stalwart Mail Server is straightforward. It requires defining a list of two or more in-memory store identifiers in the configuration. These identifiers correspond to the individual in-memory stores that make up the shard.

The following configuration settings are available for Sharded In-Memory Stores, which are specified under the store.<name> section of the configuration file:

• type: Specifies the type of database, set to "sharded-in-memory" for sharded in-memory store.
• stores: A list of in-memory store identifiers that make up the shard. Each identifier corresponds to an in-memory store backend, such as Redis or Memcached.

IMPORTANT: It is crucial to note that the order and number of in-memory stores in the configuration must remain consistent once set. Changing the order or adding/removing stores will alter the hash-to-store mapping, resulting in misplaced or inaccessible data. To maintain data integrity, careful planning and stability in the shard configuration are essential.

Example

[store."sharded-in-memory"]
type = "sharded-in-memory"
stores = ["redis1", "redis2", "redis3"]