Replace Hammer for rate limiting with custom ets bucket #3571
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,82 @@ | ||
| defmodule Plausible.RateLimit do | ||
| @moduledoc """ | ||
| Thin wrapper around `:ets.update_counter/4` and a | ||
| clean-up process to act as a rate limiter. | ||
| """ | ||
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| use GenServer | ||
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| @doc """ | ||
| Starts the process that creates and cleans the ETS table. | ||
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| Accepts the following options: | ||
| - `GenServer.options()` | ||
| - `:table` for the ETS table name, defaults to `#{__MODULE__}` | ||
| - `:clean_period` for how often to perform garbage collection | ||
| """ | ||
| @spec start_link([GenServer.option() | {:table, atom} | {:clean_period, pos_integer}]) :: | ||
| GenServer.on_start() | ||
| def start_link(opts) do | ||
| {gen_opts, opts} = | ||
| Keyword.split(opts, [:debug, :name, :timeout, :spawn_opt, :hibernate_after]) | ||
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| GenServer.start_link(__MODULE__, opts, gen_opts) | ||
| end | ||
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| @doc """ | ||
| Checks the rate-limit for a key. | ||
| """ | ||
| @spec check_rate(:ets.table(), key, scale, limit, increment) :: {:allow, count} | {:deny, limit} | ||
| when key: term, | ||
| scale: pos_integer, | ||
| limit: pos_integer, | ||
| increment: pos_integer, | ||
| count: pos_integer | ||
| def check_rate(table \\ __MODULE__, key, scale, limit, increment \\ 1) do | ||
| bucket = div(now(), scale) | ||
| full_key = {key, bucket} | ||
| expires_at = (bucket + 1) * scale | ||
| count = :ets.update_counter(table, full_key, increment, {full_key, 0, expires_at}) | ||
| if count <= limit, do: {:allow, count}, else: {:deny, limit} | ||
| end | ||
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| @impl true | ||
| def init(opts) do | ||
| clean_period = Keyword.fetch!(opts, :clean_period) | ||
| table = Keyword.get(opts, :table, __MODULE__) | ||
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| ^table = | ||
| :ets.new(table, [ | ||
| :named_table, | ||
| :set, | ||
| :public, | ||
| {:read_concurrency, true}, | ||
| {:write_concurrency, true}, | ||
| {:decentralized_counters, true} | ||
| ]) | ||
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| schedule(clean_period) | ||
| {:ok, %{table: table, clean_period: clean_period}} | ||
| end | ||
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| @impl true | ||
| def handle_info(:clean, state) do | ||
| clean(state.table) | ||
| schedule(state.clean_period) | ||
| {:noreply, state} | ||
|
There was a problem hiding this comment. Would it make sense to hibernate the process, since all it's doing is waiting another 10 minutes for the next cleanup? There was a problem hiding this comment. I haven't used process hibernation before. I'll read up on that. There was a problem hiding this comment. From a quick look, process hibernation forces a garbage collection (we have |
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| end | ||
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| defp schedule(clean_period) do | ||
| Process.send_after(self(), :clean, clean_period) | ||
| end | ||
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| defp clean(table) do | ||
| ms = [{{{:_, :_}, :_, :"$1"}, [], [{:<, :"$1", {:const, now()}}]}] | ||
| :ets.select_delete(table, ms) | ||
| end | ||
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| @compile inline: [now: 0] | ||
| defp now do | ||
| System.system_time(:millisecond) | ||
| end | ||
| end | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,67 @@ | ||
| defmodule Plausible.RateLimitTest do | ||
| use ExUnit.Case, async: true | ||
| alias Plausible.RateLimit | ||
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| @table __MODULE__ | ||
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| defp key, do: "key:#{System.unique_integer([:positive])}" | ||
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| @tag :slow | ||
| test "garbage collection" do | ||
| start_supervised!({RateLimit, clean_period: _100_ms = 100, table: @table}) | ||
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| key = key() | ||
| scale = _50_ms = 50 | ||
| limit = 10 | ||
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| for _ <- 1..3 do | ||
| assert {:allow, 1} = RateLimit.check_rate(@table, key, scale, limit) | ||
| assert [{{^key, _bucket}, _count = 1, expires_at}] = :ets.tab2list(@table) | ||
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| assert expires_at > System.system_time(:millisecond) | ||
| assert expires_at <= System.system_time(:millisecond) + 50 | ||
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| :timer.sleep(150) | ||
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| assert :ets.tab2list(@table) == [] | ||
| end | ||
| end | ||
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| describe "check_rate/3" do | ||
| setup do | ||
| start_supervised!({RateLimit, clean_period: :timer.minutes(1), table: @table}) | ||
| :ok | ||
| end | ||
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| test "increments" do | ||
| key = key() | ||
| scale = :timer.seconds(10) | ||
| limit = 10 | ||
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| assert {:allow, 1} = RateLimit.check_rate(@table, key, scale, limit) | ||
| assert {:allow, 2} = RateLimit.check_rate(@table, key, scale, limit) | ||
| assert {:allow, 3} = RateLimit.check_rate(@table, key, scale, limit) | ||
| end | ||
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| test "resets" do | ||
| key = key() | ||
| scale = 10 | ||
| limit = 10 | ||
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| assert {:allow, 1} = RateLimit.check_rate(@table, key, scale, limit) | ||
| :timer.sleep(scale * 2 + 1) | ||
| assert {:allow, 1} = RateLimit.check_rate(@table, key, scale, limit) | ||
| end | ||
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| test "denies" do | ||
| key = key() | ||
| scale = :timer.seconds(10) | ||
| limit = 3 | ||
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| assert {:allow, 1} = RateLimit.check_rate(@table, key, scale, limit) | ||
| assert {:allow, 2} = RateLimit.check_rate(@table, key, scale, limit) | ||
| assert {:allow, 3} = RateLimit.check_rate(@table, key, scale, limit) | ||
| assert {:deny, 3} = RateLimit.check_rate(@table, key, scale, limit) | ||
| end | ||
| end | ||
| end |
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I'm looking at how Hammer's table is configured:
I'm sure you've benchmarked the hell out of it, what was the difference between using
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I've only benchmarked different implementations https://github.com/ruslandoga/rate_limit, and I haven't benchmarked set vs ordered-set directly. I'll do a benchmark now.
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PR: ruslandoga/rate_limit#1