From 1729479a908195548700727c6bb6c5020f4334e6 Mon Sep 17 00:00:00 2001
From: Vlad Lazar <vlad@redpanda.com>
Date: Thu, 23 Jun 2022 13:37:40 +0100
Subject: [PATCH] prometheus.cc: Aggregate before converting to text

This patch uses the aggregation utilities introduced in the previous
patches in order to perform aggregation of counter and histogram
metrics. This step takes place before converting to text for reporting.
---
 src/core/prometheus.cc | 48 +++++++++++++++++++++++++-----------------
 1 file changed, 29 insertions(+), 19 deletions(-)

diff --git a/src/core/prometheus.cc b/src/core/prometheus.cc
index a4518c1b28a..e08a181db0b 100644
--- a/src/core/prometheus.cc
+++ b/src/core/prometheus.cc
@@ -19,6 +19,7 @@
  * Copyright (C) 2016 ScyllaDB
  */
 
+#include <seastar/core/metrics.hh>
 #include <seastar/core/prometheus.hh>
 #include <sstream>
 
@@ -592,12 +593,10 @@ future<> write_text_representation(output_stream<char>& out, const config& ctx,
             auto name = ctx.prefix + "_" + metric_family.name();
             found = false;
             histogram_aggregator histograms(metric_family.metadata().aggregate_labels);
+            counter_aggregator counters(metric_family.metadata().aggregate_labels);
             bool should_aggregate = !metric_family.metadata().aggregate_labels.empty();
-            metric_family.foreach_metric([&out, &ctx, &found, &name, &metric_family, &histograms, should_aggregate](auto value, auto value_info) mutable {
+            metric_family.foreach_metric([&out, &ctx, &found, &name, &metric_family, &histograms, &counters, should_aggregate](auto value, auto value_info) mutable {
                 std::stringstream s;
-                if (value.is_empty()) {
-                    return;
-                }
                 if (!found) {
                     if (metric_family.metadata().d.str() != "") {
                         s << "# HELP " << name << " " <<  metric_family.metadata().d.str() << "\n";
@@ -614,25 +613,36 @@ future<> write_text_representation(output_stream<char>& out, const config& ctx,
                         write_histogram(s, ctx, name, value.get_histogram(), value_info.id.labels());
                     }
                 } else {
-                    write_counter(s, ctx, name, value, value_info.id.labels());
+                    if (should_aggregate) {
+                        counters.add_counter(value, value_info.id.labels());
+                    } else {
+                        write_counter(s, ctx, name, value, value_info.id.labels());
+                    }
                 }
                 out.write(s.str()).get();
                 thread::maybe_yield();
             });
-            if (!histograms.empty()) {
-                auto name = ctx.prefix + "_" + metric_family.name();
-                std::stringstream name_help;
-                if (metric_family.metadata().d.str() != "") {
-                    name_help << "# HELP " << name << " " <<  metric_family.metadata().d.str() << "\n";
-                }
-                name_help << "# TYPE " << name << " histogram"  << "\n";
-                out.write(name_help.str()).get();
-                for (auto&& h : histograms.get_histograms()) {
-                    std::stringstream s;
-                    write_histogram(s, ctx, name, h.second, h.first);
-                    out.write(s.str()).get();
-                    thread::maybe_yield();
-                }
+
+            std::stringstream aggregated_metrics_stream;
+
+            for (auto&& h : histograms.get_histograms()) {
+                write_histogram(aggregated_metrics_stream, ctx, name, h.second, h.first);
+                out.write(aggregated_metrics_stream.str()).get();
+
+                aggregated_metrics_stream.str({});
+                aggregated_metrics_stream.clear();
+
+                thread::maybe_yield();
+            }
+
+            for (auto&& h : counters.get_counters()) {
+                write_counter(aggregated_metrics_stream, ctx, name, h.second, h.first);
+                out.write(aggregated_metrics_stream.str()).get();
+
+                aggregated_metrics_stream.str({});
+                aggregated_metrics_stream.clear();
+
+                thread::maybe_yield();
             }
         }
     });