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ApsaraDB for Redis:Terms

最終更新日:Feb 22, 2024

This topic describes the terms of ApsaraDB for Redis to help you better understand and use Redis databases.

Term

Description

instance ID

A basic unit of ApsaraDB for Redis. Each instance corresponds to a user space. Redis has limits on instance configurations, such as the number of connections, bandwidth, and CPU power. These limits vary based on different instance types. You can view the list of your instance IDs in the console.

node

The smallest building block of a Redis deployment. Redis nodes usually run on Elastic Compute Service (ECS) instances. Nodes are categorized into data nodes and proxy nodes based on their roles and functionalities.

  • Data nodes are used to deploy Redis instances. Data nodes include master and replica nodes and read replicas.

  • Proxy nodes are used to deploy self-developed proxies. For more information, see Features of proxy nodes.

shard

Each Redis cluster instance is composed of multiple shards. The architecture of each shard within a Redis cluster instance vary based on the instance type. If the instance type is High Availability, each shard consists of master and replica nodes.

For example, if the specification of a cluster instance is 8 GB Cluster (4 Shards, 2 GB per Shard) and the instance type is High Availability, the cluster instance consists of four shards, and each shard contains master and replica nodes.

deployment model

  • High availability: uses a master-replica architecture. The master node serves your workloads, whereas the replica node stays in hot standby mode to ensure high availability. If the master node fails, the system fails the workloads over to the replica node within 30 seconds after the failure occurs. This ensures the high availability of your instance.

  • Standalone: contains only a single data node. No replica nodes are provided to synchronize data in real time. Standard standalone instances are suitable for cache-only scenarios that do not require high data reliability. Standard standalone instances are available at a relatively low price.

version compatibility

Tair is compatible with open source Redis versions such as Redis 7.0, Redis 6.0, Redis 5.0, and Redis 4.0.

eviction policy

The eviction policy that is used in Tair is the same as that of open source Redis. For more information, see Key eviction.

database (DB)

Each Redis instance can contain up to 256 databases: DB 0 to DB 255. By default, data is written to DB 0.