hydra queue runner: instrument the process of loading new builds with prom

src/hydra-queue-runner/hydra-queue-runner.cc

@@ -47,6 +47,34 @@ State::PromMetrics::PromMetrics()
             .Register(*registry)
             .Add({})
     )
+    , queue_build_loads(
+        prometheus::BuildCounter()
+            .Name("hydraqueuerunner_queue_build_loads_total")
+            .Help("Number of builds loaded")
+            .Register(*registry)
+            .Add({})
+    )
+    , queue_checks_early_exits(
+        prometheus::BuildCounter()
+            .Name("hydraqueuerunner_queue_checks_early_exits_total")
+            .Help("Number of times State::getQueuedBuilds() yielded to potential bumps")
+            .Register(*registry)
+            .Add({})
+    )
+    , queue_checks_finished(
+        prometheus::BuildCounter()
+            .Name("hydraqueuerunner_queue_checks_finished_total")
+            .Help("Number of times State::getQueuedBuilds() was completed")
+            .Register(*registry)
+            .Add({})
+    )
+    , queue_max_id(
+        prometheus::BuildGauge()
+            .Name("hydraqueuerunner_queue_max_build_id_info")
+            .Help("Maximum build record ID in the queue")
+            .Register(*registry)
+            .Add({})
+    )
 {
 
 }

src/hydra-queue-runner/queue-monitor.cc

@@ -109,7 +109,10 @@ bool State::getQueuedBuilds(Connection & conn,
             auto builds_(builds.lock());
             BuildID id = row["id"].as<BuildID>();
             if (buildOne && id != buildOne) continue;
-            if (id > newLastBuildId) newLastBuildId = id;
+            if (id > newLastBuildId) {
+                newLastBuildId = id;
+                prom.queue_max_id.Set(id);
+            }
             if (builds_->count(id)) continue;
 
             auto build = std::make_shared<Build>(
@@ -138,6 +141,7 @@ bool State::getQueuedBuilds(Connection & conn,
     std::set<StorePath> finishedDrvs;
 
     createBuild = [&](Build::ptr build) {
+        prom.queue_build_loads.Increment();
         printMsg(lvlTalkative, format("loading build %1% (%2%)") % build->id % build->fullJobName());
         nrAdded++;
         newBuildsByID.erase(build->id);
@@ -308,8 +312,13 @@ bool State::getQueuedBuilds(Connection & conn,
 
         /* Stop after a certain time to allow priority bumps to be
            processed. */
-        if (std::chrono::system_clock::now() > start + std::chrono::seconds(600)) break;
+        if (std::chrono::system_clock::now() > start + std::chrono::seconds(600)) {
+            prom.queue_checks_early_exits.Increment();
+            break;
         } 
+    }
+
+    prom.queue_checks_finished.Increment();
 
     lastBuildId = newBuildsByID.empty() ? newLastBuildId : newBuildsByID.begin()->first - 1;
     return newBuildsByID.empty();

src/hydra-queue-runner/state.hh

@@ -8,6 +8,7 @@
 #include <queue>
 
 #include <prometheus/counter.h>
+#include <prometheus/gauge.h>
 #include <prometheus/registry.h>
 
 #include "db.hh"
@@ -442,6 +443,10 @@ private:
         std::shared_ptr<prometheus::Registry> registry;
 
         prometheus::Counter& queue_checks_started;
+        prometheus::Counter& queue_build_loads;
+        prometheus::Counter& queue_checks_early_exits;
+        prometheus::Counter& queue_checks_finished;
+        prometheus::Gauge& queue_max_id;
 
         PromMetrics();
     };