josevalim
Hello everyone,
I would like to propose the addition of the Registry project to Elixir:
https://github.com/elixir-lang/registry
The Registry project is a local and scalable key-value process storage in Elixir. It encapsulates 3 known use cases:
- Process registry: to register process with dynamic names. Often Elixir developers need to rely on gproc or other tools.
- Code dispatching: dispatch a module/function associated to a given key
- PubSub implementation: send messages to local processes registered under a given topic
There are probably other use cases waiting to be discovered. 
You can learn more in the documentation:
http://elixir-lang.org/docs/registry/
The project clocks only 700LOC with documentation and performs well. We have extracted, improved and generalized the patterns from Phoenix.PubSub, the implementation used to manage and publish messages to 2 million subscribers.
When benchmarking thousands of processes registering serially, it is twice slower than local atoms, albeit 33% faster than gproc. On concurrent cases, it distributes well across all cores, becoming only 15% slower than local atoms, and 3x faster than gproc on a machine with two cores (gproc seems to be serial with its default configurations so the difference will be even bigger on more cores).
Please give it a try and let us know what you think.
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JEG2
I am so excited about the possibility of having this built-in!
OvermindDL1
Ooo, so basically an Elixirfied
:gprocit looks like? That is awesome if so! ^.^EDIT: Indeed it does, a bit more simplified in the docs as I’m not seeing anything like
:gprocs local and remote distinctions or pubsub helpers and such, but it looks like the pubsub helpers can be build on what is here, and the local and remote distinctions are probably not necessary if it is naturally distributed.josevalim
Its API is quite simpler than gproc’s. There is no support for distribution as well, it is by definition local. One reason why we are hesitant on tackling any distributed registry as part of Elixir is because such is already part of the OTP team plans.
OvermindDL1
Ooo, I’ve apparently not kept up with the OTP doings, that would be fascinating.
benwilson512
What would the relationship between this and those OTP plans be once they come to fruition?
ChrisYammine
Neat! Definitely giving it a try
belaustegui
Wonderful! The implementation seems very clean and understandable
Noob question: what would be the utility of having multiple partitions for the same Registry? Looking at the code I see that the registry uses only one by default. In which cases should I use more partitions than the default one?
Qqwy
This is very interesting!
I believe it would be great to have this become part of Elixir’s core or at least the ‘officially maintained packages’, as it is a very common use case.
What was the main reason behind starting this project? In the first post you mentioned that Registry is somewhat faster than gproc: Was this (make it faster) the main reason to start building this? Or are there features that you feel are missing from gproc and other existing alternatives that are important enough to start something new?
gmile
Can you please point to a relevant discussion?
josevalim
This is local, the OTP one is distributed. You shouldn’t use the OTP one to store local data, as looking up or storing information may require messages across nodes.
On my benchmarks, the use of partitions have only been justified for the pubsub/dispatch use cases. For the unique registry, I couldn’t find a case yet where increasing the number of partitions matter. However, my current machine has only 2 cores. Maybe a partitioned unique registry may matter on machines with 16+ cores.
:gproc is a great project, albeit I find its API confusing (YMMV). If you asked me about a registry in Elixir six months ago, the answer would likely be no. So what has changed?
Being faster than gproc is a perk, although the registry was designed to scale with multiple cores. Work in the registry is always done on the client, there is no centralized entity, and that’s another useful pattern to have in hand.
In other words, there isn’t a single reason. We found a generic solution that is performant and scalable and our reaction is that it can be very useful as part of the language.