1 files changed, 29 insertions, 26 deletions
diff --git a/config/initializers/database_config.rb b/config/initializers/database_config.rb
index ce732677c74..cccd4335a7d 100644
--- a/config/initializers/database_config.rb
+++ b/config/initializers/database_config.rb
@@ -20,31 +20,34 @@ Gitlab.ee do
   end
 end
 
-# When running on multi-threaded runtimes like Puma or Sidekiq,
-# set the number of threads per process as the minimum DB connection pool size.
-# This is to avoid connectivity issues as was documented here:
-# https://github.com/rails/rails/pull/23057
-if Gitlab::Runtime.multi_threaded?
-  max_threads = Gitlab::Runtime.max_threads
-  db_config = Gitlab::Database.config ||
-      Rails.application.config.database_configuration[Rails.env]
-  previous_db_pool_size = db_config['pool']
-
-  db_config['pool'] = [db_config['pool'].to_i, max_threads].max + ENV["DB_POOL_HEADROOM"].to_i
-
-  ActiveRecord::Base.establish_connection(db_config)
-
-  current_db_pool_size = ActiveRecord::Base.connection.pool.size
-
-  log_pool_size('DB', previous_db_pool_size, current_db_pool_size)
-
-  Gitlab.ee do
-    if Gitlab::Runtime.sidekiq? && Gitlab::Geo.geo_database_configured?
-      previous_geo_db_pool_size = Rails.configuration.geo_database['pool']
-      Rails.configuration.geo_database['pool'] = max_threads
-      Geo::TrackingBase.establish_connection(Rails.configuration.geo_database)
-      current_geo_db_pool_size = Geo::TrackingBase.connection_pool.size
-      log_pool_size('Geo DB', previous_geo_db_pool_size, current_geo_db_pool_size)
-    end
+# Because of the way Ruby on Rails manages database connections, it is
+# important that we have at least as many connections as we have
+# threads. While there is a 'pool' setting in database.yml, it is not
+# very practical because you need to maintain it in tandem with the
+# number of application threads. Because of this we override the number
+# of allowed connections in the database connection pool based on the
+# configured number of application threads.
+#
+# Gitlab::Runtime.max_threads is the number of "user facing" application
+# threads the process has been configured with. We also have auxiliary
+# threads that use database connections. Because it is not practical to
+# keep an accurate count of the number auxiliary threads as the
+# application evolves over time, we just add a fixed headroom to the
+# number of user-facing threads. It is OK if this number is too large
+# because connections are instantiated lazily.
+
+headroom = (ENV["DB_POOL_HEADROOM"].presence || 10).to_i
+calculated_pool_size = Gitlab::Runtime.max_threads + headroom
+
+db_config = Gitlab::Database.config ||
+            Rails.application.config.database_configuration[Rails.env]
+
+db_config['pool'] = calculated_pool_size
+ActiveRecord::Base.establish_connection(db_config)
+
+Gitlab.ee do
+  if Gitlab::Runtime.sidekiq? && Gitlab::Geo.geo_database_configured?
+    Rails.configuration.geo_database['pool'] = calculated_pool_size
+    Geo::TrackingBase.establish_connection(Rails.configuration.geo_database)
   end
 end