Delete Redis Cache Using Ruby (Detailed Guide w/ Code Examples)

Use Case(s)

In a web application, caching is used to speed up repeated queries and reduce database load. However, there might be scenarios where you need to delete the cache. For instance:

1. If your data changes frequently, it may become outdated fast so you need to delete the cache regularly.
2. During development, you might want to clear the cache to test if your app works properly without it.

Code Examples

The following examples use the redis gem for Ruby.

1. Deleting a single key:

require 'redis'
redis = Redis.new
redis.set('key', 'value')  # sets a value
dis.delete('key')  # deletes the key-value pair

This will remove the key 'key' from the Redis store.

2. Deleting multiple keys:

require 'redis'
redis = Redis.new
redis.mset('key1', 'value1', 'key2', 'value2')  # sets multiple values
redis.del('key1', 'key2')  # deletes multiple keys at once

This will remove both 'key1' and 'key2' from the Redis store.

3. Deleting all keys:

require 'redis'
redis = Redis.new
redis.flushdb

This command will empty the entire Redis store.

Best Practices

Instead of deleting the entire cache, selectively delete keys as this can help avoid unnecessary database load.

Avoid using flushdb or flushall in production as they will lock your Redis instance while it clears the database.

Common Mistakes

1. Not handling exceptions when deleting keys. Ensure you are using proper error handling to avoid breaking the application in case a key isn't found or the Redis server is down.
2. Using flushall instead of flushdb. The flushall command not only deletes data from the current database but also from all other databases on the same Redis instance.

FAQs

1. Can I delete keys with a specific pattern? Yes, you can find keys with a specific pattern using the keys method and then delete them. For example:

require 'redis'
redis = Redis.new
keys = redis.keys('*pattern*')
keys.each { |key| redis.del(key) }

However, be aware that using keys can potentially block the server for a long time if called against large databases.

2. What happens if I try to delete a key that does not exist? Redis will simply return 0 and continue. No error is thrown because of this.