PHP Redis: Getting All Databases (Detailed Guide w/ Code Examples)

Use Case(s)

Redis does not directly support 'get all databases' operation, because the databases in Redis are identified by an index and there is no command to retrieve indexes of all existing databases. However, it's common for PHP developers using the Redis extension to want to interact with different databases within a Redis instance. This can include switching between databases using the select function.

Code Examples

You're usually specifying the database when you're connecting. Here's how you do it:

$redis = new Redis(); $redis->connect('', 6379); $redis->select(0); // switch to DB 0

Now if you want to switch to another database, you can call select again:

$redis->select(1); // switch to DB 1

Please note that the number of databases can be configured in your redis configuration file (redis.conf) by the parameter 'databases'. The default number of databases is 16.

Best Practices

Remember that Redis is not a relational database. The multiple database feature is meant for separate logical uses within the same application, not for large scale data separation. If you need isolation, it's better to run multiple Redis instances.

Common Mistakes

A frequent mistake is to assume that Redis supports operations across multiple databases like SQL JOINs. It doesn't. Operations in Redis are database-specific and cannot span multiple databases.


Q: Can I get the number of all existing databases in Redis via PHP?

A: No, Redis does not support this directly. The number of databases is defined in the Redis configuration file and defaults to 16.

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