feat: use iodata for metrics export

This prevents memory bloat form creating all intermediate binaries that
are later dropped. Instead we try to reuse as much of binaries as
possible and then let the VM do the concatenation if needed.

VERSION

@@ -1 +1 @@
-2.1.5
+2.1.6

lib/supavisor/monitoring/prom_ex.ex

@@ -58,7 +58,7 @@ defmodule Supavisor.Monitoring.PromEx do
     end
   end
 
-  @spec get_metrics() :: String.t()
+  @spec get_metrics() :: iodata()
   def get_metrics do
     metrics_tags =
       case Application.fetch_env(:supavisor, :metrics_tags) do
@@ -71,7 +71,7 @@ defmodule Supavisor.Monitoring.PromEx do
     metrics =
       PromEx.get_metrics(__MODULE__)
       |> String.split("\n")
-      |> Enum.map_join("\n", &parse_and_add_tags(&1, def_tags))
+      |> Enum.map(&parse_and_add_tags(&1, def_tags))
 
     Supavisor.Monitoring.PromEx.ETSCronFlusher
     |> PromEx.ETSCronFlusher.defer_ets_flush()
@@ -81,7 +81,7 @@ defmodule Supavisor.Monitoring.PromEx do
 
   @spec do_cache_tenants_metrics() :: list
   def do_cache_tenants_metrics do
-    metrics = get_metrics() |> String.split("\n")
+    metrics = get_metrics() |> IO.iodata_to_binary() |> String.split("\n")
 
     pools =
       Registry.select(Supavisor.Registry.TenantClients, [{{:"$1", :_, :_}, [], [:"$1"]}])
@@ -109,7 +109,7 @@ defmodule Supavisor.Monitoring.PromEx do
     end
   end
 
-  @spec parse_and_add_tags(String.t(), String.t()) :: String.t()
+  @spec parse_and_add_tags(String.t(), String.t()) :: iodata()
   defp parse_and_add_tags(line, def_tags) do
     case Regex.run(~r/(?!\#)^(\w+)(?:{(.*?)})?\s*(.+)$/, line) do
       nil ->
@@ -122,10 +122,10 @@ defmodule Supavisor.Monitoring.PromEx do
           if tags == "" do
             def_tags
           else
-            "#{tags},#{def_tags}"
+            [tags, ",", def_tags]
           end
 
-        "#{key}{#{tags}} #{value}"
+        [key, "{", tags, "}", value, "\n"]
     end
   end
 

lib/supavisor_web/controllers/metrics_controller.ex

@@ -56,6 +56,6 @@ defmodule SupavisorWeb.MetricsController do
   end
 
   def merge_node_metrics({_, {_node, metrics}}, acc) do
-    [metrics <> "\n" | acc]
+    [metrics, "\n" | acc]
   end
 end