Deleting Redis Keys By Pattern in Ruby (Detailed Guide w/ Code Examples)

Use Case(s)

A common use case for deleting keys by a pattern in Redis using the Ruby programming language includes cases where you need to remove many keys at once that share a common pattern. This could be due to data invalidation, data versioning, or cleanup tasks.

Code Examples

In Ruby, you can use the 'redis' gem to interact with a Redis database. Here are ways to delete keys based on a pattern:

1. Using SCAN and DEL commands:

   require 'redis'
   
   redis = Redis.new(host: 'localhost', port: 6379)
   
   cursor = '0'
   loop do
     cursor, keys = redis.scan(cursor, match: 'your_pattern*')
     keys.each { |key| redis.del(key) } unless keys.empty?
   
     break if cursor == '0'
   end

   This code starts a scan operation from the beginning (cursor '0'). For each key that matches the pattern ('your_pattern*'), it deletes the key. The loop ends when the scan has completed and cursor returns to '0'.

2. Using KEYS and DEL commands (not recommended for production):

   require 'redis'
   
   redis = Redis.new(host: 'localhost', port: 6379)
   
   keys = redis.keys('your_pattern*')
   redis.del(keys) unless keys.empty?

   This example uses the KEYS command to find all keys matching the pattern, and the DEL command to delete them. However, using KEYS in a production environment is not recommended as it may block the server when processing large keyspaces.

Best Practices

• Avoid the KEYS command in production environments because it's blocking. Use the SCAN command instead because it allows for incremental iteration.

• Be careful when deleting keys. Make sure the pattern doesn’t unintentionally match other keys.

Common Mistakes

• Using KEYS in a production environment can lead to performance issues.

• Not checking if the keys array is empty before running the DEL command. If you pass an empty array to the DEL command, you might get unexpected results.

FAQs

Q: Can I use wildcards in my pattern?

A: Yes, you can use '' as a wildcard character in your pattern. For example, 'user:' will match all keys that start with 'user:'.