Speedup iterating over `WorkSet` (#5559)

lib/sidekiq/api.rb

@@ -1103,24 +1103,31 @@ module Sidekiq
 
     def each(&block)
       results = []
+      procs = nil
+      all_works = nil
+
       Sidekiq.redis do |conn|
-        procs = conn.sscan_each("processes").to_a
-        procs.sort.each do |key|
-          valid, workers = conn.pipelined { |pipeline|
-            pipeline.exists?(key)
+        procs = conn.sscan_each("processes").to_a.sort
+
+        all_works = conn.pipelined do |pipeline|
+          procs.each do |key|
             pipeline.hgetall("#{key}:work")
-          }
-          next unless valid
-          workers.each_pair do |tid, json|
-            hsh = Sidekiq.load_json(json)
-            p = hsh["payload"]
-            # avoid breaking API, this is a side effect of the JSON optimization in #4316
-            hsh["payload"] = Sidekiq.load_json(p) if p.is_a?(String)
-            results << [key, tid, hsh]
           end
         end
       end
 
+      procs.zip(all_works).each do |key, workers|
+        workers.each_pair do |tid, json|
+          next if json.empty?
+
+          hsh = Sidekiq.load_json(json)
+          p = hsh["payload"]
+          # avoid breaking API, this is a side effect of the JSON optimization in #4316
+          hsh["payload"] = Sidekiq.load_json(p) if p.is_a?(String)
+          results << [key, tid, hsh]
+        end
+      end
+
       results.sort_by { |(_, _, hsh)| hsh["run_at"] }.each(&block)
     end