From 9fdbff3f917a1bc8b1ac6d09a84da44bd169c855 Mon Sep 17 00:00:00 2001
From: Andreas Wachowski <andreas.wachowski@gmail.com>
Date: Mon, 11 Dec 2023 13:47:18 +0100
Subject: [PATCH] Add support for gauge aggregation setting (#6)

In prometheus-client-mmap `Prometheus::Client::Registry#gauge` has a fourth parameter `multiprocess_mode` which handles the aggregation.

See:
* https://gitlab.com/gitlab-org/ruby/gems/prometheus-client-mmap/-/blob/v0.17.0/lib/prometheus/client/registry.rb#L43
* https://gitlab.com/gitlab-org/ruby/gems/prometheus-client-mmap/-/blob/v0.17.0/lib/prometheus/client/gauge.rb#L12

Not all settings already used by yabeda plugins are supported by prometheus-mmap gem (namely `most_recent`), so map metric aggregation setting from Yabeda to Prometheus-mmap names in best effort.

---------

Co-authored-by: Andrey Novikov <envek@envek.name>
---
 lib/yabeda/prometheus/mmap/adapter.rb | 18 +++++++++++++++++-
 spec/yabeda/prometheus/mmap_spec.rb   | 22 +++++++++++++++++++++-
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/lib/yabeda/prometheus/mmap/adapter.rb b/lib/yabeda/prometheus/mmap/adapter.rb
index 378b1b2..ea15db7 100644
--- a/lib/yabeda/prometheus/mmap/adapter.rb
+++ b/lib/yabeda/prometheus/mmap/adapter.rb
@@ -35,7 +35,8 @@ def register_gauge!(metric)
           registry.gauge(
             build_name(metric),
             metric.comment,
-            build_tags(metric.tags)
+            build_tags(metric.tags),
+            gauge_aggregation_mode(metric.aggregation)
           )
         end
 
@@ -86,6 +87,21 @@ def debug!
           end
         end
 
+        private
+
+        def gauge_aggregation_mode(yabeda_mode)
+          case yabeda_mode
+          when nil, :most_recent # TODO: Switch to most_recent when supported: https://gitlab.com/gitlab-org/ruby/gems/prometheus-client-mmap/-/issues/36
+            :all
+          when :min, :max, :all, :liveall
+            yabeda_mode
+          when :sum
+            :livesum
+          else
+            raise ArgumentError, "Unsupported gauge aggregation mode #{yabeda_mode.inspect}"
+          end
+        end
+
         Yabeda.register_adapter(:prometheus, new)
       end
     end
diff --git a/spec/yabeda/prometheus/mmap_spec.rb b/spec/yabeda/prometheus/mmap_spec.rb
index 0cf4f5c..2ded663 100644
--- a/spec/yabeda/prometheus/mmap_spec.rb
+++ b/spec/yabeda/prometheus/mmap_spec.rb
@@ -13,7 +13,8 @@
 
       gauge :gauge,
             comment: 'Gauge',
-            tags: [:gtag]
+            tags: [:gtag],
+            aggregation: :sum
 
       histogram :histogram,
                 comment: 'Histogram',
@@ -32,9 +33,28 @@
       expect(Yabeda.test_counter.values).to eq(
         { { ctag: :'ctag-value' } => 1 }
       )
+    end
+  end
+
+  context 'gauge' do
+    it do
       expect(Yabeda.test_gauge.values).to eq(
         { { gtag: :'gtag-value' } => 123 }
       )
+    end
+
+    it 'passes aggregation to multiprocess_mode' do
+      expect(
+        Yabeda
+        .adapters[:prometheus].registry
+        .instance_variable_get(:@metrics)[:test_gauge]
+        .instance_variable_get(:@multiprocess_mode)
+      ).to eq(:livesum)
+    end
+  end
+
+  context 'histogram' do
+    it do
       expect(Yabeda.test_histogram.values).to eq(
         { { htag: :'htag-value' } => 7 }
       )