Command Routing
Valkey GLIDE can determine and route commands efficiently to nodes in a Valkey (or Redis) cluster. This section will go over how command routing works in Valkey GLIDE.
How GLIDE Routes commands
Section titled “How GLIDE Routes commands”As a Valkey cluster topology can change over time, new nodes can be added or removed and the primary node owning a specific slot may change. To handle this, GLIDE clients are topology aware. They maintain a map of the cluster state and route commands to the primary node. When topology changes (e.g., due to scaling operations or failovers), GLIDE clients update their internal cluster map to ensure commands are always routed correctly.
For example, in a cluster Valkey setup, data are sharded across multiple nodes. A command like client.set("user:100", "active") will be routed only
to the primary node containing the slot for the key user:100.
Read Strategy
Section titled “Read Strategy”By default, GLIDE routes all read commands to the primary nodes. While this guarantees strong consistency it can lead to higher load especially if there are many write operations on the primary node. To optimize read performance and distribute the load, GLIDE clients support different read strategies that allow reads to be directed to replica nodes.
| Strategy | Description |
|---|---|
Primary (Default) | Always read from primary, in order to get the freshest data. |
PreferReplica | Spread requests between all replicas in a round robin manner. If no replica is available, route the requests to the primary. |
AZAffinity | Spread the read requests between replicas in the same client’s availability zone in a round robin manner, falling back to other replicas or the primary if needed. |
AzAffinityReplicaAndPrimary | Spread the read requests among nodes within the client’s Availability Zone (AZ) in a round robin manner, prioritizing local replicas, then the local primary, and falling back to any replica or the primary if needed. |
Multi-Slot Commands
Section titled “Multi-Slot Commands”In Valkey or Redis Cluster mode, certain commands can operate on multiple keys that may be spread across different hash slots. When these commands receive keys that map to multiple slots, they are called multi-slot commands. GLIDE supports efficient handling of these commands routing them across the cluster.
For more on multi-slot commands, see this section.