Hardware Requirements - Redis

Sizing considerations

General database sizing {#general-sizing}

Factors to consider when sizing your database.

Dataset size – Your limit should be greater than your dataset size to leave room for overhead.
Database throughput – High throughput needs more shards, leading to a higher memory limit.
[Modules]({{< relref "/operate/oss_and_stack/stack-with-enterprise" >}}) – Using modules with your database consumes more memory.
[Database clustering]({{< relref "/operate/rs/7.22/databases/durability-ha/clustering" >}}) – Allows you to spread your data into shards across multiple nodes.
[Database replication]({{< relref "/operate/rs/7.22/databases/durability-ha/replication" >}}) – Enabling replication doubles memory consumption.

Active-Active database sizing {#active-active-sizing}

Additional factors for sizing Active-Active databases:

[Active-Active replication]({{< relref "/operate/rs/7.22/databases/active-active" >}}) – Requires double the memory of regular replication, which can be up to two times (2x) the original data size per instance.
[Database replication backlog]({{< relref "/operate/rs/7.22/databases/durability-ha/replication#database-replication-backlog" >}}) – For synchronization between shards. By default, this is set to 1% of the database size.
[Active-Active replication backlog]({{< relref "/operate/rs/7.22/databases/active-active/manage#replication-backlog" >}}) – For synchronization between clusters. By default, this is set to 1% of the database size.

{{<note>}} Active-Active databases have a lower threshold for activating the eviction policy, because it requires propagation to all participating clusters. The eviction policy starts to evict keys when one of the Active-Active instances reaches 80% of its memory limit. {{</note>}}

Sizing databases with Auto Tiering enabled {#redis-on-flash-sizing}

Additional factors for sizing databases with Auto Tiering enabled:

[Database persistence]({{< relref "/operate/rs/7.22/databases/configure/database-persistence#redis-on-flash-data-persistence" >}}) – Auto Tiering uses dual database persistence where both the primary and replica shards persist to disk. This may add some processor and network overhead, especially in cloud configurations with network-attached storage.