# Code Review: Batching GenServer

**URL:** <https://forum.elixirforum.com/t/code-review-batching-genserver/61306>\
**Category:** Questions\
**Tags:** code-review\
**Created:** [January 30, 2024, 1:48am UTC](https://forum.elixirforum.com/t/code-review-batching-genserver/61306 "2024-01-30T01:48:23Z")\
**Posts on this page:** 1\
**Showing post:** 3

<div class="post-metadata">

**Author:** ![ydg33](https://forum.elixirforum.com/letter_avatar_proxy/v4/letter/y/91b2a8/32.png) [@ydg33](https://forum.elixirforum.com/u/ydg33)\
**Post date:** [January 30, 2024, 4:11am UTC](https://forum.elixirforum.com/t/code-review-batching-genserver/61306/3 "2024-01-30T04:11:17Z")

</div>

Thanks for replying!! Yea no worries, it’s a bit of code, thanks for looking it over! Sorry if I am misunderstanding your suggestions in my reply below!

> it seems like this is something you might be able to handle with core library functions before reaching for GenServer, `Enum.chunk_every` and `Task.async_stream` maybe

Yea I was wondering about this! I don’t think so unfortunately, because while `Enum.chunk_every` would help me split up a list of items into chunks, it wouldn’t help me batch a sequence of individual calls. I want to make a bunch of individual calls like so:

```elixir
out1 = api(in1)
out2 = api(in2)
...
outN = api(inN)

```

and behind the scenes batch them into one API call. I actually already use `chunk_every` and `Task.async_stream` in my manual batching implementation, but it’s annoying because I have to keep track of keys for each input. In particular I can’t just write

```elixir
inputs
|> Enum.map(fn input -> Task.async(fn -> api(input) end) end)
|> Task.await_many()

```

… anymore, instead I have to write something like

```elixir
inputs
|> fn input -> {key_for_input(input), input} end
|> Enum.chunk_every(50)
|> Task.async_stream (fn batch
  # the api only cares about the values...
  api(Enum.map(batch, &(elem(&1, 1)))
  # but we need to reassociate the output values with their keys afterwards
  |> Enum.zip(Enum.map(batch, &(elem(&1, 0)))
)
|> Enum.to_list
|> Enum.flat_map(...)

```

And I have to write this for every new API call…

I think I can’t use `handle_cast` because I do care about the results, e.g. I want to still be able to write code like this:

```elixir
out1 = api(in1)
out2 = api(in2)
...
outN = api(inN)

```

I just want it to be batched behind the scenes.

I saw this library for Erlang: [GitHub - rabbitmq/gen-batch-server: A generic batching server for Erlang and Elixir · GitHub](https://github.com/rabbitmq/gen-batch-server) but I tried to understand what was going on and it seems very lightly documented.

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