大部分支持VIP的交换机也能支持主用系统或备用系统的策略，以便流量跑到主用系统那里，除非它不可用或验证失败。
Most switches that support a VIP can also support a policy of primary system or secondary system, so that traffic goes to the primary system unless it is unavailable or fails the validation.
方法和块能被“完全”编译，因此可以在eval不可用时使用define_method等一系列方法。
Method and block bodies can be compiled "completely", so it's possible to use define_method and friends even when eval isn't available.
如果你够幸运工个甚至能找到原先的文件并保存，把它救回来，将其标识为不可用恢复它。
If you're lucky, they can even find the file and save it, bring it back, mark it not available, undelete it.
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