A pure-Crystal implementation of the Redis protocol

1. Add the dependency to your shard.yml:

   dependencies:
     redis:
       github: jgaskins/redis

2. Run shards

require "redis"

redis = Redis::Client.new # Defaults to `localhost` port 6379

redis.set "foo", "bar"
redis.get "foo" # => "bar"

redis.incr "counter" # => 1
redis.incr "counter" # => 2
redis.decr "counter" # => 1

redis.del "foo", "counter" # => 2

To mitigate latency with multiple queries whose inputs and outputs are completely independent of each other, you can "pipeline" your queries by sending them all at once before reading them. To do this, you can use the pipeline method:

redis.pipeline do |pipe|
  pipe.incr "foo"
  pipe.set "bar", "baz"
  pipe.lpush "my-list", "my value"
end

The return value of pipeline will be an array containing the values of each of those calls in the order they were sent. So in this case, it might be [1, nil, 2] to match the return values of incr, set, and lpush, respectively.

The Redis MULTI command begins a transaction, so you can use the multi method to execute a transaction against the server:

redis.multi do |txn|
  txn.set "foo", "bar"
  txn.incr "baz"
  txn.lpush "my-list", "my value"
end

The transaction is automatically committed with EXEC at the end of the block. If an exception occurs within the block, the transaction will be rolled back with DISCARD before exiting the block.

You may also call txn.discard, which will effectively disable the transaction (all further methods called on the transaction do nothing), but will not exit the block. You will need to exit the block explicitly with break if there are operations within the block that cannot be rolled back, such as sending an email or sending a request to a third-party API.

The reason for this is that the only way to exit a containing block from an inner method in Crystal is to raise an exception, and this library chooses not to use exceptions for flow control.

To use a Redis server that isn't at localhost:6379, pass a URI to the client. For example, if you store it in your shell environment:

redis = Redis::Client.new(URI.parse(ENV["REDIS_URL"]))

# ... or ...

redis = Redis::Client.from_env("REDIS_URL")

To connect via SSL, make sure you use the rediss:// URL scheme. If your Redis server requires a password or uses a different database slot than 0, make sure you include them in the URL:

redis = Redis::Client.new(URI.parse("rediss://:[email protected]/3"))

The Redis::Client maintains a connection pool, so there is no need to run your own within your application. When you execute a command on the Redis::Client, it is automatically executed against a connection. When you execute a pipeline or transaction with multi, all commands within that block will automatically be routed to the same connection.

Configuration

For this shard, we use the following default setting (outside of the Standard Lib defaults);

max_idle_pool_size = 25

You can override this manually using the URI parameters. All other settings follow the DB::Pool defaults.

The behaviour of the connection pool can be configured from a set of query string parameters in the connection URI.

See Crystal guides to learn more.

Example

pool_params = "?initial_pool_size=1&max_pool_size=10&checkout_timeout=10&retry_attempts=2&retry_delay=0.5&max_idle_pool_size=50"
redis = Redis::Client.new(URI.parse("redis://localhost:6379/0#{pool_params}"))

Recommendations

If you encounter any issues, keep these setting the same;

• initial_pool_size
• max_pool_size
• max_idle_pool_size

Example:

initial_pool_size = 50
max_pool_size = 50
max_idle_pool_size = 50

The Redis::Client uses a pool of Redis::Connection under the hood. Within Redis::Connection we create a TCPSocket, which can accept keepalive params. The TCP keepalive settings can help you mitigate Redis connection stability issues.

NOTE: This behaviour is disabled by default. See Configuration below on how to enable it.

Configuration

For this shard, we use the following override setting;

You can override this manually using the URI parameters. The settings above have proven to have good results in production environments. However, every environment is different, so tweaking these settings may be necessary.

See Crystal API to learn more.

Example

params = "?keepalive=true&keepalive_count=5&keepalive_idle=10&keepalive_interval=15"

redis = Redis::Client.new(URI.parse("redis://localhost:6379/0#{params}"))
# or direct connections
redis = Redis::Connection.new(URI.parse("redis://localhost:6379/0#{params}"))

Recommendations

Enable this setting with the defaults if you are encountering connection issues.

Example:

params = "?keepalive=true"

redis = Redis::Client.new(URI.parse("redis://localhost:6379/0#{params}"))
# or direct connections
redis = Redis::Connection.new(URI.parse("redis://localhost:6379/0#{params}"))

Make sure you have a Redis or KeyDB server running locally on port 6379.

Redis must be installed with a stack server for the full text search (ft) and time series modules (ts) in order for all specs to run.

You can use this for your docker-compose file

redis:
  image: redis/redis-stack-server
  ports:
    - "6379:6379"

Install the redis-stack from homebrew

1. Fork it (https://github.com/jgaskins/redis/fork)
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

• Jamie Gaskins - creator and maintainer