ruby-on-rails - Railsdelayed_job 作业执行的确切顺序

Question

我正在使用 Collectiveidea 的 Delayed_Job 版本: https://github.com/collectiveidea/delayed_job

有人可以告诉我当 worker 选择下一份工作时使用的实际标准吗？我假设它类似于“SELECT id FROM dependent_jobs WHERE run_at > NOW() ORDER BYpriority ASC, run_at ASC LIMIT 1”(首先按优先级选择，其次按 run_at 时间选择)，但我无法准确找到是什么经过考虑的。我在 GitHub 上的代码中做了一些研究，但还没有找到下一个作业的实际查询。对一些事情感到好奇，包括“created_at”、“attempts”或“failed_at”是否会影响优先级。 (我意识到我不太可能找到实际的 SQL，只是一种简单的方法来表示我假设的查询的作用)。

其次，这个 gem 的实际文档有什么好的来源吗？对于 Rails 中常用的东西，我见过的文档非常稀疏。

Answer 1

对源代码的一些挖掘在 backend/active_record.rb 中显示了这一点:

    scope :ready_to_run, lambda {|worker_name, max_run_time|
      where(['(run_at <= ? AND (locked_at IS NULL OR locked_at < ?) OR locked_by = ?) AND failed_at IS NULL', db_time_now, db_time_now - max_run_time, worker_name])
    }
    scope :by_priority, order('priority ASC, run_at ASC')

    # Find a few candidate jobs to run (in case some immediately get locked by others).
    def self.find_available(worker_name, limit = 5, max_run_time = Worker.max_run_time)
      scope = self.ready_to_run(worker_name, max_run_time)
      scope = scope.scoped(:conditions => ['priority >= ?', Worker.min_priority]) if Worker.min_priority
      scope = scope.scoped(:conditions => ['priority <= ?', Worker.max_priority]) if Worker.max_priority

      ::ActiveRecord::Base.silence do
        scope.by_priority.all(:limit => limit)
      end
    end

此外，backend/base.rb 中的这一点也很有趣:

    def reserve(worker, max_run_time = Worker.max_run_time)
      # We get up to 5 jobs from the db. In case we cannot get exclusive access to a job we try the next.
      # this leads to a more even distribution of jobs across the worker processes
      find_available(worker.name, 5, max_run_time).detect do |job|
        job.lock_exclusively!(max_run_time, worker.name)
      end
    end

reserve 由工作人员调用以选择下一个工作。