From c4c01f88942a1ad23cc58e26b5c64f39d58f046c Mon Sep 17 00:00:00 2001
From: Oliver Peate <odlp@users.noreply.github.com>
Date: Wed, 2 Dec 2020 16:50:00 +0000
Subject: [PATCH] Warn on boot if maxmemory policy is not 'noeviction' (#4752)

---
 lib/sidekiq/cli.rb |  5 +++++
 test/test_cli.rb   | 26 ++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/lib/sidekiq/cli.rb b/lib/sidekiq/cli.rb
index 936215efe..5b8361353 100644
--- a/lib/sidekiq/cli.rb
+++ b/lib/sidekiq/cli.rb
@@ -62,6 +62,11 @@ def run(boot_app: true)
       ver = Sidekiq.redis_info["redis_version"]
       raise "You are connecting to Redis v#{ver}, Sidekiq requires Redis v4.0.0 or greater" if ver < "4"
 
+      maxmemory_policy = Sidekiq.redis_info["maxmemory_policy"]
+      if maxmemory_policy != "noeviction"
+        logger.warn "'noeviction' maxmemory policy is recommended (current policy: '#{maxmemory_policy}'). See: https://github.com/mperham/sidekiq/wiki/Using-Redis#memory"
+      end
+
       # Since the user can pass us a connection pool explicitly in the initializer, we
       # need to verify the size is large enough or else Sidekiq's performance is dramatically slowed.
       cursize = Sidekiq.redis_pool.size
diff --git a/test/test_cli.rb b/test/test_cli.rb
index 832ab4fe0..716ae32fb 100644
--- a/test/test_cli.rb
+++ b/test/test_cli.rb
@@ -481,6 +481,32 @@ def logdev
           assert_includes @logdev.string, "Booted Rails #{::Rails.version} application in production environment"
         end
       end
+
+      describe 'checking maxmemory policy' do
+        it 'warns if the policy is not noeviction' do
+          redis_info = { "maxmemory_policy" => "allkeys-lru", "redis_version" => "6" }
+
+          Sidekiq.stub(:redis_info, redis_info) do
+            subject.stub(:launch, nil) do
+              subject.run
+            end
+          end
+
+          assert_includes @logdev.string, "'noeviction' maxmemory policy is recommended (current policy: 'allkeys-lru')"
+        end
+
+        it 'silent if the policy is noeviction' do
+          redis_info = { "maxmemory_policy" => "noeviction", "redis_version" => "6" }
+
+          Sidekiq.stub(:redis_info, redis_info) do
+            subject.stub(:launch, nil) do
+              subject.run
+            end
+          end
+
+          refute_includes @logdev.string, "'noeviction' maxmemory policy is recommended"
+        end
+      end
     end
 
     describe 'signal handling' do