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Load Balance


When the load in a single machine can't bear so much traffics, a natural solution is to distribute load on several machines.

It introduced a new problem to us: how to distribute traffics to several machines? This kind of problem is called load balancing.


Round-Robin DNS

The simplest …


HyperLogLog is an algorithm that can solve Count Distinct problem. A Count Distinct problem is something like getting number 5 for a data set like [1, 3, 2, 1, 5, 2, 4], for it has [1, 2, 3, 4, 5] 5 elements.

HyperLogLog can provide estimated count on a very …

Count Distinct


Count-distinct problem is a problem of finding the number of distinct elements in a data set or data stream, within which you might possibly see some repeated elements. For example, [1, 3, 2, 1, 5, 2, 4] has 5 distinct elements [1, 2, 3, 4, 5].


Unix commands …