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  <title>On Consistent Hashing - Alexandr Poltavsky, software developer</title>

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      Alexandr Poltavsky <br/>
      Software Developer <br/>
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<h2>On Consistent Hashing</h2>

<p>Consistent hashing is an algorithm that allows to amortize the cost of object movement
in case a bucket becomes unavailable (offline). It's frequently used to distribute
load on servers in case of a server going down.</p>

<p>The common description and implementation of <a href="https://en.wikipedia.org/wiki/Consistent_hashing">consistent hashing</a>
uses a circle (array) filled with bucket locations in random order.</p>

<p>If you think about it then it becomes clear that, what this algorithm actually does
is introduce a walking order for the buckets. Essentially it is an open addressing
method with random probing. So what you do is something along the lines:</p>

<pre><code>srand( hash( object ) ); //introduce random probing order

size_t location = -1;

for(size_t i=0; i &lt; number_of_tries; i++) {

  location = rand() % table_size;

  if( check_location( location ) ) break; //or if( server_is_online( location ) ) break;

};

if( location == -1 ) throw( ... );

...
</code></pre>

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