Redis: Do Not Open Circuit on OOM

lib/semian/redis.rb

@@ -23,6 +23,13 @@ def initialize(semian_identifier, *args)
 
   class OutOfMemoryError < Redis::CommandError
     include ::Semian::AdapterError
+
+    # An OutOfMemoryError is a fast failure. We don't want to open circuits
+    # because that would block read and dequeue operations that could help
+    # Redis recover from the OOM state.
+    def marks_semian_circuits?
+      false
+    end
   end
 
   class ConnectionError < Redis::BaseConnectionError

lib/semian/redis_client.rb

@@ -13,6 +13,14 @@ def marks_semian_circuits?
   end
 
   OutOfMemoryError.include(::Semian::AdapterError)
+  OutOfMemoryError.class_eval do
+    # An OutOfMemoryError is a fast failure. We don't want to open circuits
+    # because that would block read and dequeue operations that could help
+    # Redis recover from the OOM state.
+    def marks_semian_circuits?
+      false
+    end
+  end
 
   class ReadOnlyError < RedisClient::ConnectionError
     # A ReadOnlyError is a fast failure and we don't want to track these errors so that we can reconnect

test/adapters/redis_test.rb

@@ -105,37 +105,45 @@ def test_command_errors_does_not_open_the_circuit
     end
   end
 
-  def test_command_errors_because_of_oom_do_open_the_circuit
+  def test_command_errors_because_of_oom_do_not_open_the_circuit
+    # OOM errors should NOT open the circuit, because:
+    # 1. They are fast failures (no benefit from failing fast)
+    # 2. Blocking reads/dequeues prevents recovery from OOM
     client = connect_to_redis!
 
     with_maxmemory(1) do
-      ERROR_THRESHOLD.times do
+      (ERROR_THRESHOLD + 1).times do
         exception = assert_raises(::Redis::OutOfMemoryError) do
           client.set("foo", "bar")
         end
 
         assert_equal(:redis_testing, exception.semian_identifier)
       end
 
-      assert_raises(::Redis::CircuitOpenError) do
+      # Circuit should NOT be open - we should still get OOM errors, not CircuitOpenError
+      assert_raises(::Redis::OutOfMemoryError) do
         client.set("foo", "bla")
       end
     end
   end
 
-  def test_script_errors_because_of_oom_do_open_the_circuit
+  def test_script_errors_because_of_oom_do_not_open_the_circuit
+    # OOM errors should NOT open the circuit, because:
+    # 1. They are fast failures (no benefit from failing fast)
+    # 2. Blocking reads/dequeues prevents recovery from OOM
     client = connect_to_redis!
 
     with_maxmemory(1) do
-      ERROR_THRESHOLD.times do
+      (ERROR_THRESHOLD + 1).times do
         exception = assert_raises(::Redis::OutOfMemoryError) do
           client.eval("return redis.call('set', 'foo', 'bar');")
         end
 
         assert_equal(:redis_testing, exception.semian_identifier)
       end
 
-      assert_raises(::Redis::CircuitOpenError) do
+      # Circuit should NOT be open - we should still get OOM errors, not CircuitOpenError
+      assert_raises(::Redis::OutOfMemoryError) do
         client.eval("return redis.call('set', 'foo', 'bar');")
       end
     end