feat: add p99 and std dev columns to performance stats (#77)

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- P99 + standard deviation columns in performance stats — `p99` and `Std Dev` columns added to the stats table; both are sortable; high std dev flags inconsistent jobs worth investigating
 - Failed job trend chart — "Failures — last 12 hours" sparkline added to the Solid Queue dashboard card below the throughput sparkline; bars render in the danger color to make failure spikes immediately visible
 - Error frequency report — `GET /failed_jobs/errors` groups all failed jobs by exception class and message prefix, showing count and an expandable sample backtrace per group; links through to a filtered failed jobs list via `?error_class=`; the failed jobs index gains an "Error Summary" button and shows an active-filter breadcrumb with a clear link
 

app/controllers/solid_stack_web/stats_controller.rb

@@ -1,6 +1,6 @@
 module SolidStackWeb
   class StatsController < ApplicationController
-    SORTABLE_COLUMNS = %w[class_name count avg p50 p95 min max].freeze
+    SORTABLE_COLUMNS = %w[class_name count avg p50 p95 p99 stddev min max].freeze
 
     def index
       @sort      = params[:sort].presence_in(SORTABLE_COLUMNS) || "p95"
@@ -18,14 +18,17 @@ def build_stats(jobs)
       jobs.group_by(&:class_name).map do |class_name, group|
         durations = group.map { |j| (j.finished_at - j.created_at).to_f }.sort
         count     = durations.size
+        avg = durations.sum / count
         {
           class_name: class_name,
           count:      count,
-          avg:        durations.sum / count,
+          avg:        avg,
           min:        durations.first,
           max:        durations.last,
           p50:        percentile(durations, 50),
-          p95:        percentile(durations, 95)
+          p95:        percentile(durations, 95),
+          p99:        percentile(durations, 99),
+          stddev:     stddev(durations, avg)
         }
       end
     end
@@ -35,5 +38,11 @@ def percentile(sorted, pct)
       k = (sorted.size - 1) * pct / 100.0
       sorted[k.floor] + (sorted[k.ceil] - sorted[k.floor]) * (k - k.floor)
     end
+
+    def stddev(durations, avg)
+      return 0.0 if durations.size < 2
+      variance = durations.sum { |d| (d - avg)**2 } / durations.size
+      Math.sqrt(variance)
+    end
   end
 end

app/views/solid_stack_web/stats/index.html.erb

@@ -12,6 +12,8 @@
           ["avg",        "Avg"],
           ["p50",        "p50"],
           ["p95",        "p95"],
+          ["p99",        "p99"],
+          ["stddev",     "Std Dev"],
           ["min",        "Min"],
           ["max",        "Max"]
         ].each do |col, label| %>
@@ -35,6 +37,8 @@
           <td class="sqw-muted"><%= format_duration(row[:avg]) %></td>
           <td class="sqw-muted"><%= format_duration(row[:p50]) %></td>
           <td><strong><%= format_duration(row[:p95]) %></strong></td>
+          <td class="sqw-muted"><%= format_duration(row[:p99]) %></td>
+          <td class="sqw-muted"><%= format_duration(row[:stddev]) %></td>
           <td class="sqw-muted"><%= format_duration(row[:min]) %></td>
           <td class="sqw-muted"><%= format_duration(row[:max]) %></td>
         </tr>

spec/requests/solid_stack_web/stats_spec.rb

@@ -60,5 +60,24 @@ def create_finished(class_name: "MyJob", duration: 10)
       get "#{engine_root}/stats"
       expect(response.body).to match(/\d+(\.\d+)?s|ms/)
     end
+
+    it "renders p99 and Std Dev column headers" do
+      create_finished(class_name: "MyJob")
+      get "#{engine_root}/stats"
+      expect(response.body).to include("p99")
+      expect(response.body).to include("Std Dev")
+    end
+
+    it "accepts sort by p99" do
+      create_finished(class_name: "MyJob")
+      get "#{engine_root}/stats", params: { sort: "p99", direction: "desc" }
+      expect(response).to have_http_status(:ok)
+    end
+
+    it "accepts sort by stddev" do
+      create_finished(class_name: "MyJob")
+      get "#{engine_root}/stats", params: { sort: "stddev", direction: "desc" }
+      expect(response).to have_http_status(:ok)
+    end
   end
 end