ruby-on-rails – 长期运行到死亡的迁移/ find_each

2019年8月3日 163次阅读

使用PostgreSQL运行Rails 3,

我进行了迁移,更新了数百万条小记录.

Record.find_each do |r|
  r.doing_incredibly_complex_stuff
  r.save!
  puts "#{r.id} updated"
end

由于我认为ActiveRecord在事务中包装了这样的更新,因此“提交”时间非常长并且所占用的内存很大,而在上面的示例中,每个记录都已“打印”在屏幕上.

那么,我可以在事务外运行这个find_each – 虽然它非常安全 – 节省了大量的“提交”时间和内存吗？

一种ActiveRecord :: Base.without_transaction做…;结束我猜:-)

要么 ：
我错了,迁移不包含在事务中,我看到的时间只是SQL更新语句适用？

编辑：它似乎与事务无关,这是我在中断迁移后得到的堆栈跟踪,当所有内容都已打印在屏幕上并且RAM从500MB可用空间减少到~30MB时：

IRB::Abort: abort then interrupt!!
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activesupport-3.0.4/lib/active_support/whiny_nil.rb:46:in `call'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activesupport-3.0.4/lib/active_support/whiny_nil.rb:46:in `method_missing'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/connection_adapters/postgresql_adapter.rb:978:in `flatten'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/connection_adapters/postgresql_adapter.rb:978:in `block in select'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/connection_adapters/postgresql_adapter.rb:977:in `map'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/connection_adapters/postgresql_adapter.rb:977:in `select'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/connection_adapters/abstract/database_statements.rb:7:in `select_all'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/connection_adapters/abstract/query_cache.rb:56:in `select_all'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/base.rb:467:in `find_by_sql'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/relation.rb:64:in `to_a'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/activerecord-3.0.4/lib/active_record/relation.rb:356:in `inspect'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/railties-3.0.4/lib/rails/commands/console.rb:44:in `start'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/railties-3.0.4/lib/rails/commands/console.rb:8:in `start'
from /Users/clement/.rvm/gems/ruby-1.9.2-p136@gemset/gems/railties-3.0.4/lib/rails/commands.rb:23:in `<top (required)>'
from script/rails:6:in `require'
from script/rails:6:in `<main>'

编辑(2)：哇.事实证明它很长,因为find_each在迭代后返回所有元素.

我试过了 ：

Record.tap do |record_class|
  record_class.find_each do |r|
    r.doing_incredibly_complex_stuff
    r.save!
    puts "#{r.id} updated"
  end
end
=> Record(id: integer, ...)

所以它按预期立即回馈了控制台. 🙂

但后来我仍然看到一种奇怪的行为：RAM不会释放.相反,一旦我退出,RAM仍然会下降……

也许我的水龙头解决方案不满意？它还在大规模选择吗？我如何避免find_each之后的质量选择？

谢谢！

最佳答案 ActiveRecord :: Migration和find_each都没有做任何事情来将您的代码包装在数据库事务中. r.save！将包含在涵盖保存的任何级联效果的单个事务中.

如上面的注释中所述,使用update_all或原始执行将更快地进行批量更新.我无法判断这是否适合您正在做的事情.此外,如果您遇到内存问题,您应该能够在find_each上调整批量大小并查看它是否有效.如果没有,你可能会在某处抓住那些物体.

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