Quick stats api. (#4936)

* Lazily fetch slow stats later.

* Put calls to lazy load into stat method.

* Add test for workers_size.

lib/sidekiq/api.rb

@@ -8,7 +8,7 @@ require "base64"
 module Sidekiq
   class Stats
     def initialize
-      fetch_stats!
+      fetch_stats_fast!
     end
 
     def processed
@@ -51,7 +51,8 @@ module Sidekiq
       Sidekiq::Stats::Queues.new.lengths
     end
 
-    def fetch_stats!
+    # O(1) redis calls
+    def fetch_stats_fast!
       pipe1_res = Sidekiq.redis { |conn|
         conn.pipelined do
           conn.get("stat:processed")
@@ -64,6 +65,34 @@ module Sidekiq
         end
       }
 
+
+      default_queue_latency = if (entry = pipe1_res[6].first)
+        job = begin
+                Sidekiq.load_json(entry)
+              rescue
+                {}
+              end
+        now = Time.now.to_f
+        thence = job["enqueued_at"] || now
+        now - thence
+      else
+        0
+      end
+
+      @stats = {
+        processed: pipe1_res[0].to_i,
+        failed: pipe1_res[1].to_i,
+        scheduled_size: pipe1_res[2],
+        retry_size: pipe1_res[3],
+        dead_size: pipe1_res[4],
+        processes_size: pipe1_res[5],
+
+        default_queue_latency: default_queue_latency
+      }
+    end
+
+    # O(number of processes + number of queues) redis calls
+    def fetch_stats_slow!
       processes = Sidekiq.redis { |conn|
         conn.sscan_each("processes").to_a
       }
@@ -83,30 +112,13 @@ module Sidekiq
       workers_size = pipe2_res[0...s].sum(&:to_i)
       enqueued = pipe2_res[s..-1].sum(&:to_i)
 
-      default_queue_latency = if (entry = pipe1_res[6].first)
-        job = begin
-          Sidekiq.load_json(entry)
-        rescue
-          {}
-        end
-        now = Time.now.to_f
-        thence = job["enqueued_at"] || now
-        now - thence
-      else
-        0
-      end
-      @stats = {
-        processed: pipe1_res[0].to_i,
-        failed: pipe1_res[1].to_i,
-        scheduled_size: pipe1_res[2],
-        retry_size: pipe1_res[3],
-        dead_size: pipe1_res[4],
-        processes_size: pipe1_res[5],
+      @stats[:workers_size] = workers_size
+      @stats[:enqueued] = enqueued
+    end
 
-        default_queue_latency: default_queue_latency,
-        workers_size: workers_size,
-        enqueued: enqueued
-      }
+    def fetch_stats!
+      fetch_stats_fast!
+      fetch_stats_slow!
     end
 
     def reset(*stats)
@@ -126,6 +138,10 @@ module Sidekiq
     private
 
     def stat(s)
+      if (s == :enqueued || s == :workers_size) &&
+         @stats.present? && @stats[s].nil?
+        fetch_stats_slow!
+      end
       @stats[s]
     end
 

test/test_api.rb

@@ -16,6 +16,7 @@ describe 'API' do
       assert_equal 0, s.failed
       assert_equal 0, s.enqueued
       assert_equal 0, s.default_queue_latency
+      assert_equal 0, s.workers_size
     end
 
     describe "processed" do
@@ -71,6 +72,19 @@ describe 'API' do
       end
     end
 
+    describe "workers_size" do
+      it 'retrieves the number of busy workers' do
+        Sidekiq.redis do |c|
+          c.sadd("processes", "process_1")
+          c.sadd("processes", "process_2")
+          c.hset("process_1", "busy", 1)
+          c.hset("process_2", "busy", 2)
+        end
+        s = Sidekiq::Stats.new
+        assert_equal 3, s.workers_size
+      end
+    end
+
     describe "queues" do
       it "is initially empty" do
         s = Sidekiq::Stats::Queues.new