Deleting Keys by Prefix in Redis using Ruby (Detailed Guide w/ Code Examples)

Use Case(s)

In Redis, keys are used to store data. However, there may be cases where you want to delete all keys that have a common prefix. This is useful when managing grouped data in your Redis instance, for instance, session data prefixed with 'session:', or user data with 'user:'.

Code Examples

Here is an example on how to delete keys by prefix using the Redis gem in Ruby:

require 'redis'

redis = Redis.new

# Add some keys
redis.set('prefix:1', 'value1')
redis.set('prefix:2', 'value2')
redis.set('prefix:3', 'value3')
redis.set('noprefix:4', 'value4')

# Get keys by prefix
keys_with_prefix = redis.keys('prefix:*')

# Delete keys by prefix
deleted_keys_count = redis.del(keys_with_prefix) unless keys_with_prefix.empty?
puts deleted_keys_count # will print 3

This script creates a new Redis connection, sets a few key-value pairs, retrieves keys with a specific prefix and then deletes them.

Best Practices

While the above method works, it's not advisable to use it in production if the database contains large amounts of data because it can block the server for a long time, especially the 'KEYS' command. A better way is to use 'SCAN' command which allows iterations through keys in the database without blocking server.

Common Mistakes

One common mistake is forgetting to check if the array of keys is empty before passing it to the del function. If keys_with_prefix is empty, the del function will raise a Redis::CommandError.

FAQs

1. Can I delete keys by suffix in Redis? While Redis does not support deleting keys by suffix directly, you can do it programmatically by retrieving all keys, filtering by your conditions, and then deleting them.

2. Is there a performance difference between KEYs and SCAN commands? Yes, the SCAN command is generally more efficient than the KEYS command because it allows the server to stay responsive to other incoming commands while iterating through large collections of keys.