From f82fff2d1bc42b6b48926ffe73ce5f23d95fb75f Mon Sep 17 00:00:00 2001
From: Ajay Krishnan <ajay@krishnan.ca>
Date: Wed, 24 Jun 2026 00:04:40 -0700
Subject: [PATCH] Warn instead of raising when the connection pool is smaller
 than the thread pool

Solid Queue refused to boot when the Active Record connection pool was
smaller than the worker thread pool. This blocked legitimate setups, such
as I/O-bound queues that run many threads against a deliberately small pool.

Per the discussion in #736, downgrade the check from a validation error to
a SolidQueue.logger warning emitted once on the boot path in
Supervisor.start, so undersized configurations boot while still surfacing
the advisory. valid? stays purely about whether we can boot.

Closes #736
---
 lib/solid_queue/configuration.rb | 15 +++++++--------
 lib/solid_queue/supervisor.rb    |  2 ++
 test/unit/configuration_test.rb  | 23 +++++++++++++++++++----
 3 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/lib/solid_queue/configuration.rb b/lib/solid_queue/configuration.rb
index e63a000ca..300bfd100 100644
--- a/lib/solid_queue/configuration.rb
+++ b/lib/solid_queue/configuration.rb
@@ -6,7 +6,6 @@ class Configuration
 
     validate :ensure_configured_processes
     validate :ensure_valid_recurring_tasks
-    validate :ensure_correctly_sized_thread_pool
 
     class Process < Struct.new(:kind, :attributes)
       def instantiate
@@ -69,6 +68,13 @@ def standalone?
       mode.fork? || @options[:standalone]
     end
 
+    def warn_about_undersized_thread_pool
+      if (db_pool_size = SolidQueue::Record.connection_pool&.size) && db_pool_size < estimated_number_of_threads
+        SolidQueue.logger.warn "Solid Queue is configured to use #{estimated_number_of_threads} threads but the " +
+          "database connection pool is #{db_pool_size}. Increase it in `config/database.yml`"
+      end
+    end
+
     private
       attr_reader :options
 
@@ -88,13 +94,6 @@ def ensure_valid_recurring_tasks
         end
       end
 
-      def ensure_correctly_sized_thread_pool
-        if (db_pool_size = SolidQueue::Record.connection_pool&.size) && db_pool_size < estimated_number_of_threads
-          errors.add(:base, "Solid Queue is configured to use #{estimated_number_of_threads} threads but the " +
-            "database connection pool is #{db_pool_size}. Increase it in `config/database.yml`")
-        end
-      end
-
       def default_options
         {
           mode: ENV["SOLID_QUEUE_SUPERVISOR_MODE"] || :fork,
diff --git a/lib/solid_queue/supervisor.rb b/lib/solid_queue/supervisor.rb
index ae17ec95c..695a066a4 100644
--- a/lib/solid_queue/supervisor.rb
+++ b/lib/solid_queue/supervisor.rb
@@ -13,6 +13,8 @@ def start(**options)
         configuration = Configuration.new(**options)
 
         if configuration.valid?
+          configuration.warn_about_undersized_thread_pool
+
           klass = configuration.mode.fork? ? ForkSupervisor : AsyncSupervisor
           klass.new(configuration).tap(&:start)
         else
diff --git a/test/unit/configuration_test.rb b/test/unit/configuration_test.rb
index 34f69658b..bf2c6b8ec 100644
--- a/test/unit/configuration_test.rb
+++ b/test/unit/configuration_test.rb
@@ -165,14 +165,29 @@ class ConfigurationTest < ActiveSupport::TestCase
     assert_not configuration.valid?
     assert_equal [ "No processes configured" ], configuration.errors.full_messages
 
-    # Not enough DB connections
+    # Not enough DB connections: still valid so boot is not blocked
     configuration = SolidQueue::Configuration.new(workers: [ { queues: "background", threads: 50, polling_interval: 10 } ])
-    assert_not configuration.valid?
-    assert_match /Solid Queue is configured to use \d+ threads but the database connection pool is \d+. Increase it in `config\/database.yml`/,
-      configuration.errors.full_messages.first
+    assert configuration.valid?
+  end
+
+  test "warns on boot when the database pool is smaller than the thread pool" do
+    log = StringIO.new
+    with_solid_queue_logger(ActiveSupport::Logger.new(log)) do
+      configuration = SolidQueue::Configuration.new(workers: [ { queues: "background", threads: 50, polling_interval: 10 } ])
+      configuration.warn_about_undersized_thread_pool
+    end
+
+    assert_match /Solid Queue is configured to use \d+ threads but the database connection pool is \d+\. Increase it in `config\/database.yml`/, log.string
   end
 
   private
+    def with_solid_queue_logger(logger)
+      old_logger, SolidQueue.logger = SolidQueue.logger, logger
+      yield
+    ensure
+      SolidQueue.logger = old_logger
+    end
+
     def assert_processes(configuration, kind, count, **attributes)
       processes = configuration.configured_processes.select { |p| p.kind == kind }
       assert_equal count, processes.size