Understanding Redis’s Default 16 Databases: Origin, Configuration, and Best Practices

1. Origin of the 16 Databases

Redis is a dictionary‑structured storage server; a single Redis instance provides multiple dictionaries that can be addressed independently, similar to having several databases in a relational DBMS. By default Redis creates 16 such logical databases.

The number can be changed by editing the redis/redis.conf file’s databases setting and restarting the server.

2. Correct Understanding of Redis “Database” Concept

Redis does not allow custom names for databases; they are identified only by numeric indices, so developers must keep their own mapping of which data resides in which DB. All databases share the same access password, meaning a client can either access all databases or none.

To switch databases, the client uses the SELECT command, e.g.:

# 切库
redis> SELECT 1 # 默认0号db，切换为1号db
OK
redis [1] > GET username # 从1号库中获取 username
(nil)

The FLUSHALL command clears data from every logical database in the instance, which differs from relational databases where each database is cleared independently.

3. Multiple Databases in Cluster Mode

In Redis Cluster mode only a single logical database (db0) exists; the SELECT command is not supported. Other limitations include restricted key‑batch operations, limited Lua scripting, and a single‑level replication topology.

4. Summary

Redis defaults to 16 logical databases, configurable via the databases parameter in the configuration file. These databases act as namespaces rather than isolated stores, so different applications should use separate Redis instances. In cluster deployments only db0 is available, and multiple logical databases are not supported.