坑：用来做(page id)<=>(pagePtr)映射的map有两种实现，一种是map （内部红黑树，排序map相当于pq）unordered_map（hashmap）。后者巨麻烦需要自己提供hash function。 http://blog.csdn.net/happykocola/article/details/74188452
一个简单的实现pair hash的方法： https://stackoverflow.com/questions/20590656/error-for-hash-function-of-pair-of-ints
有关map和unordered_map选择的分析： http://thispointer.com/map-vs-unordered_map-when-to-choose-one-over-another/
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自定义key 需要写comparator
http://thispointer.com/stdmap-tutorial-part-3-using-user-defined-class-objects-as-key-in-stdmap/自定义hash
http://thispointer.com/using-unordered_set-with-custom-hasher-and-comparision-function/
ssh upload:
Ref: https://www.cnblogs.com/magicc/p/6490566.html
scp /path/filename username@servername:/path/
具体来讲， server端:~/就是上传根目录。
