Speed up find_job, closes #4259

This API has been in Sidekiq Pro for a number of years; I think it is fair to promote certain changes with such a huge positive impact to OSS.

Changes.md

@@ -5,6 +5,12 @@
 HEAD
 ---------
 
+- Dramatically speed up SortedSet#find\_job(jid) by using Redis's ZSCAN
+  support, approx 10x faster. [#4259]
+```
+zscan   0.179366   0.047727   0.227093 (  1.161376)
+enum    8.522311   0.419826   8.942137 (  9.785079)
+```
 - Respect rails' generators `test_framework` option and gracefully handle extra `worker` suffix on generator [#4256]
 - Add ability to sort 'Enqueued' page on Web UI by position in the queue [#4248]
 - Support `Client.push_bulk` with different delays [#4243]

lib/sidekiq/api.rb

@@ -593,11 +593,16 @@ module Sidekiq
 
     ##
     # Find the job with the given JID within this sorted set.
-    #
-    # This is a slow, inefficient operation.  Do not use under
-    # normal conditions.  Sidekiq Pro contains a faster version.
+    # This is a slower O(n) operation.  Do not use for app logic.
     def find_job(jid)
-      detect { |j| j.jid == jid }
+      Sidekiq.redis do |conn|
+        conn.zscan_each(name, match: "*#{jid}*", count: 100) do |entry, score|
+          job = JSON.parse(entry)
+          matched = job["jid"] == jid
+          return SortedEntry.new(self, score, entry) if matched
+        end
+      end
+      nil
     end
 
     def delete_by_value(name, value)

test/test_api.rb

@@ -341,6 +341,19 @@ describe 'API' do
       assert_equal 1, ds.size
     end
 
+    it 'can find a scheduled job by jid' do
+      10.times do |idx|
+        ApiWorker.perform_in(idx, 1)
+      end
+
+      job_id = ApiWorker.perform_in(5, 1)
+      job = Sidekiq::ScheduledSet.new.find_job(job_id)
+      assert_equal job_id, job.jid
+
+      ApiWorker.perform_in(100, 1, 'jid' => 'jid_in_args')
+      assert_nil Sidekiq::ScheduledSet.new.find_job('jid_in_args')
+    end
+
     it 'can remove jobs when iterating over a sorted set' do
       # scheduled jobs must be greater than SortedSet#each underlying page size
       51.times do