Wednesday, July 24, 2013

Scala Redis client goes non blocking : uses Akka IO

scala-redis is getting a new non blocking version based on a kernel implemented with the new Akka IO. The result is that all APIs are non blocking and return a Future. We are trying to keep the API as close to the blocking version as possible. But bits rot and some of the technical debt need to be repaid. We have cleaned up some of the return types which had unnecessary Option[] wrappers, made some improvements and standardizations on the API type signatures and also working on making the byte array manipulation faster using akka.util.ByteString at the implementation level. We also have plans of using the Akka IO pipeline for abstracting the various stages of handling Redis protocol request and response.

As of today we have quite a bit ready for review by the users. The APIs may change a bit here and there, but the core APIs are up there. There are a few areas which have not yet been implemented like PubSub or clustering. Stay tuned for more updates on this blog .. Here are a few code snippets that demonstrate the usage of the APIs ..

Non blocking get/set

@volatile var callbackExecuted = false

val ks = (1 to 10).map(i => s"client_key_$i")
val kvs = ks.zip(1 to 10)

val sets: Seq[Future[Boolean]] = kvs map {
  case (k, v) => client.set(k, v)
}

val setResult = Future.sequence(sets) map { r: Seq[Boolean] =>
  callbackExecuted = true
  r
}

callbackExecuted should be (false)
setResult.futureValue should contain only (true)
callbackExecuted should be (true)

callbackExecuted = false
val gets: Seq[Future[Option[Long]]] = ks.map { k => client.get[Long](k) }
val getResult = Future.sequence(gets).map { rs =>
  callbackExecuted = true
  rs.flatten.sum
}

callbackExecuted should be (false)
getResult.futureValue should equal (55)
callbackExecuted should be (true)

Composing through sequential combinators

val key = "client_key_seq"
val values = (1 to 100).toList
val pushResult = client.lpush(key, 0, values:_*)
val getResult = client.lrange[Long](key, 0, -1)

val res = for {
  p <- pushResult.mapTo[Long]
  if p > 0
  r <- getResult.mapTo[List[Long]]
} yield (p, r)

val (count, list) = res.futureValue
count should equal (101)
list.reverse should equal (0 to 100)

Error handling using Promise Failure

val key = "client_err"
val v = client.set(key, "value200")
v.futureValue should be (true)

val x = client.lpush(key, 1200)
val thrown = evaluating { x.futureValue } should produce [TestFailedException]
thrown.getCause.getMessage should equal ("ERR Operation against a key holding the wrong kind of value")
Feedbacks welcome, especially on the APIs and their usage. All code are in Github with all tests in the test folder. Jisoo Park (@guersam) has been doing an awesome job contributing a lot to all the goodness that's there in the repo. Thanks a lot for all the help ..

6 comments:

Anonymous said...

Hi. I've been looking into upgrading from the blocking client. However, I don't understand how to pass the client around my code as a parameter anymore. Since 'RedisOps' is private, I can't seem to refer to it, and the only way to construct it
seems to be from the RedisClient companion, where it also
constructs a new RedisClient.

What am I missing here? :)

Debasish Ghosh said...

Thanks for reporting .. will get to you shortly.

Debasish Ghosh said...

Opened an issue on Github .. https://github.com/debasishg/scala-redis-nb/issues/49 .. will be addressed soon. You can track it ..

Anonymous said...

Thank you, sir.

Alexis said...

Very cool. I will have to get this to our team. I don't think they know yet. Thank you for sharing!

Srinivas Nandina said...

Does it support connecting through twemproxy to talk to multiple redis nodes (having keys partitioned across noodes)?