instance method build_async_executor

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 718
        def build_async_executor
          case ActiveRecord.async_query_executor
          when :multi_thread_pool
            if @db_config.max_threads > 0
              Concurrent::ThreadPoolExecutor.new(
                min_threads: @db_config.min_threads,
                max_threads: @db_config.max_threads,
                max_queue: @db_config.max_queue,
                fallback_policy: :caller_runs
              )
            end
          when :global_thread_pool
            ActiveRecord.global_thread_pool_async_query_executor
          end
        end