feat(deferred): Improve default retry strategy

lib/rage/deferred/task.rb

@@ -31,12 +31,9 @@
 # ```
 #
 module Rage::Deferred::Task
-  MAX_ATTEMPTS = 5
+  MAX_ATTEMPTS = 15
   private_constant :MAX_ATTEMPTS
 
-  BACKOFF_INTERVAL = 5
-  private_constant :BACKOFF_INTERVAL
-
   # @private
   CONTEXT_KEY = :__rage_deferred_execution_context
 
@@ -191,7 +188,9 @@ def __next_retry_in(attempts, exception)
 
     # @private
     def __default_backoff(attempt)
-      rand(BACKOFF_INTERVAL * 2**attempt) + 1
+      # Use 1-indexed attempt for the formula as per issue #251
+      retry_attempt = attempt + 1
+      (retry_attempt**4) + 10 + (rand(15) * retry_attempt)
     end
   end
 end

spec/deferred/task_spec.rb

@@ -44,17 +44,24 @@ def perform(arg, kwarg:)
   end
 
   describe ".__next_retry_in" do
-    it "returns the next retry interval with exponential backoff" do
-      expect(task_class.__next_retry_in(0, nil)).to be_between(1, 5)
-      expect(task_class.__next_retry_in(1, nil)).to be_between(1, 10)
-      expect(task_class.__next_retry_in(2, nil)).to be_between(1, 20)
-      expect(task_class.__next_retry_in(3, nil)).to be_between(1, 40)
-      expect(task_class.__next_retry_in(4, nil)).to be_between(1, 80)
+    it "returns the next retry interval with polynomial backoff" do
+      # New formula: (attempt+1)**4 + 10 + rand(15) * (attempt+1)
+      # attempt 0 -> 1^4 + 10 + rand(15)*1 = 11-25
+      expect(task_class.__next_retry_in(0, nil)).to be_between(11, 25)
+      # attempt 1 -> 2^4 + 10 + rand(15)*2 = 26-54
+      expect(task_class.__next_retry_in(1, nil)).to be_between(26, 54)
+      # attempt 2 -> 3^4 + 10 + rand(15)*3 = 91-133
+      expect(task_class.__next_retry_in(2, nil)).to be_between(91, 133)
+      # attempt 3 -> 4^4 + 10 + rand(15)*4 = 266-322
+      expect(task_class.__next_retry_in(3, nil)).to be_between(266, 322)
+      # attempt 4 -> 5^4 + 10 + rand(15)*5 = 635-705
+      expect(task_class.__next_retry_in(4, nil)).to be_between(635, 705)
     end
 
     it "returns nil when attempts exceed max" do
-      expect(task_class.__next_retry_in(5, nil)).to be_between(1, 160)
-      expect(task_class.__next_retry_in(6, nil)).to be_nil
+      # With MAX_ATTEMPTS=15, attempt 15 should still return backoff
+      expect(task_class.__next_retry_in(15, nil)).to be_between(50635, 50845)
+      expect(task_class.__next_retry_in(16, nil)).to be_nil
     end
   end
 
@@ -167,7 +174,7 @@ def perform(arg, kwarg:)
 
       it "__next_retry_in uses default backoff for unmatched" do
         interval = task_class.__next_retry_in(1, StandardError.new)
-        expect(interval).to be_between(1, 10)
+        expect(interval).to be_between(26, 54)
       end
 
       it "__next_retry_in enforces max_retries even with custom interval" do