Verify connection pool sizing, fixes #3917

Changes.md

@@ -6,6 +6,7 @@ HEAD
 -----------
 
 - **Decrease default concurrency from 25 to 10** [#3892]
+- Verify connection pool sizing upon startup [#3917]
 - Smoother scheduling for large Sidekiq clusters [#3889]
 - Switch Sidekiq::Testing impl from alias\_method to Module#prepend, for resiliency [#3852]
 - Update Sidekiq APIs to use SCAN for scalability [#3848, ffiller]

lib/sidekiq/cli.rb

@@ -80,6 +80,12 @@ module Sidekiq
       ver = Sidekiq.redis_info['redis_version']
       raise "You are using Redis v#{ver}, Sidekiq requires Redis v2.8.0 or greater" if ver < '2.8'
 
+      # 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
+      needed = Sidekiq.options[:concurrency] + 2
+      raise "Your pool of #{cursize} Redis connections is too small, please increase the size to at least #{needed}" if cursize < needed
+
       # cache process identity
       Sidekiq.options[:identity] = identity
 

sidekiq.gemspec

@@ -18,6 +18,6 @@ Gem::Specification.new do |gem|
   gem.required_ruby_version = ">= 2.2.2"
 
   gem.add_dependency 'redis', '>= 3.3.5', '< 5'
-  gem.add_dependency 'connection_pool', '~> 2.2', '>= 2.2.0'
+  gem.add_dependency 'connection_pool', '~> 2.2', '>= 2.2.2'
   gem.add_dependency 'rack-protection', '>= 1.5.0'
 end