In a Ruby application using Redis as a data store, you might have stored data with keys following certain naming conventions or patterns. For example, you may have prefixed user-related data with 'user:', session-related data with 'session:', and so on. In such cases, you may need to fetch all keys starting with a particular prefix.
To get all keys starting with a specific string, Redis provides the
KEYS command which accepts a pattern. Here's how you can use it with the
redis-rb gem in Ruby:
In this example, we're connecting to a local Redis instance and using the
keys method with a pattern 'user:' to get all keys that start with 'user:'. The '' is a wildcard character that matches any sequence of characters.
While the KEYS command can be incredibly useful, it’s important to note that it may affect performance when run against large databases because it's a blocking operation. Instead, consider using the SCAN command for production environments if you need to retrieve keys matching a pattern. The SCAN command iteratively scans the database and returns a cursor that you can pass back to iterate over the next batch of keys.
This example uses the SCAN command to get all keys starting with 'user:' in a non-blocking manner.
One common mistake is to use the KEYS command in production code which can lead to performance issues. As mentioned above, it's better to use SCAN for such operations.
Q: Can I use other patterns with the
A: Yes, you can use any pattern supported by Redis. For example, 'user:?' matches 'user:x' but not 'user:xx'. '[abc]*' matches any key starting with 'a', 'b', or 'c'.