Redis client for Scala built on top of Cats Effect, Fs2 and Lettuce (formerly Fs2 Redis) -> https://redis4cats.profunktor.dev/
Thank you @gvolpe for great documentation on codecs. Having read all of it I will take your advices at I will do my own serialisation/deserialisation because I will be using your library in my Scala Play application and the class dependency inject the redis client is a Singleton class. So I only want one Redis client active at any time and be able to re-use it. Thank you sir.
Hi @mk9023_gitlab , that's a good question. The library doesn't provide this option at the moment but it should be easy to add support for it. The underlying Redis client takes in a
ClientOptions as an argument which has the following defaults: public static final boolean DEFAULT_PING_BEFORE_ACTIVATE_CONNECTION = false;
public static final boolean DEFAULT_AUTO_RECONNECT = true;
public static final boolean DEFAULT_CANCEL_CMD_RECONNECT_FAIL = false;
public static final boolean DEFAULT_PUBLISH_ON_SCHEDULER = false;
public static final boolean DEFAULT_SUSPEND_RECONNECT_PROTO_FAIL = false;
public static final int DEFAULT_REQUEST_QUEUE_SIZE = Integer.MAX_VALUE;
public static final DisconnectedBehavior DEFAULT_DISCONNECTED_BEHAVIOR = DisconnectedBehavior.DEFAULT;
public static final SocketOptions DEFAULT_SOCKET_OPTIONS = SocketOptions.create();
public static final SslOptions DEFAULT_SSL_OPTIONS = SslOptions.create();
public static final TimeoutOptions DEFAULT_TIMEOUT_OPTIONS = TimeoutOptions.create();
public static final int DEFAULT_BUFFER_USAGE_RATIO = 3;
I can work on it and release it as part of the upcoming RC3 so you can try it out if you wish to
also I have a problem now. I am trying to integration your library with my Scala Play application. What I am finding is that for every HTTP request, the library tries to make new connection to Redis every time. This is not acceptable for me as it takes then 1 or 2 seconds to connect and then once command is done then library is closing connection. What I like is for library to keep connection to Redis open for duration of web application running. Is this possible sir?
The scope of use is the scope of the Resource lifetime. It's similar to java try-with-resources or python context managers.
The code should instead accept a redis client as a constructor parameter, and reuse the same one. use would be called in one place, near your main method of your application.
See this for more: https://typelevel.org/blog/2018/06/07/shared-state-in-fp.html
Here's a full-stack example application (from the excellent "Practical FP in scala" book)
https://github.com/gvolpe/pfps-shopping-cart/blob/master/modules/core/src/main/scala/shop/Main.scala
https://github.com/gvolpe/pfps-shopping-cart/blob/master/modules/core/src/main/scala/shop/Main.scala
If you aren't using IOApp you can still do it, you'd instead use one of the unsafeRun methods in your java-ish main method.
And if your application is set up so that some framework has main and you don't control things, that's more complicated to set up, and it won't be as clean, but can be made to work as you want using whatever tool's dependency injection stuff
Yes, I am not sure if you are familiar with Scala Play web framework but I can create Module where I can create a Redis4Cats client and create Redis connection there. Once created then I can dependency inject into my classes. I think this is what I should do. I will experiemnting.
you can stash those in a var, then tie them into the hooks
super not a fan of play's dep injection style - fp scala (tbh all scala, and I've done it well in python too...) is much easier if you just use constructor parameters rather than all the magic and ceremony
@Daenyth thanks with your advices I got it Redis4Cats working nicely with Scala Play framework. I'm wondering if I can use a different logger other than SLF4J with https://github.com/ChristopherDavenport/log4cats . I want to use this: https://logging.apache.org/log4j/2.x/ - will this be possible with Redis4Cats. I tried but I don't know how. Thanks
implicit val log4jInstance: Log[IO] = new Log[IO] {...}
If the automated CI release goes well, it'll be on Maven Central quite soon :rocket:
Hey, has anyone ever seen a 2 second delay when closing the redis connection? After the logs about releasing
Commands and Redis, there’s a pretty precise and stable delay of 2 seconds before the release returns. I can reproduce this behaviour in a k8s deployed service with AWS ElastiCache, locally against a dockered redis and even in the redis4cats RedisSpec, so I assume it’s either a bug or some unfortunate configuration?
Background: Due to the use of blocking redis commands like
brPopLPush, we open a new redis connection for certain requests. This works reasonably fast when connecting, but takes this extra time while shutting down the Resource[..., RedisCommands[...]]
Any reasons why the delay exists?
Still digging deeper, but I’m pretty sure it’s the 2s from
DefaultClientResources.shutdown() (Line 584) – it’s an overload to a method which allows passing some timeouts. Maybe redis4cats should expose a way to configure these timeouts, would be very simple to pass them down to lettuce, not much code in between. Do you already have any plans to create some redis4cats configuration class which could optionally be passed when creating the client?
In the meantime, I’m thinking of
.starting the release into a separate fiber to bypass the delay it causes in the business logic
Configuring the client is already possible @ybasket so it may be just one of the config options Lettuce exposes? https://redis4cats.profunktor.dev/client.html#client-configuration
If you want bincompat you need the config class people interact with to be a trait with builder-style methods
Adding new fields to a case class replaces the old
copy signature, is the bincompat break
cats folks could probably give more ideas on how to work around that conveniently