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    <blockquote> <p>I am looking for a more in depth reason as to why the cooked up method may be more likely to generate collisions given the same degrees of freedom as a Guid.</p> </blockquote> <p>First, as others have noted, <code>Random</code> is not thread-safe; using it from multiple threads can cause it to corrupt its internal data structures so that it always produces the same sequence. </p> <p>Second, <code>Random</code> is seeded based on the current time. Two instances of <code>Random</code> created within the same millisecond (recall that a millisecond is several <em>million</em> processor cycles on modern hardware) will have the same seed, and therefore will produce the same sequence.</p> <p>Third, I lied. <code>Random</code> is not seeded based on the current time; it is seeded based on <em>the amount of time the machine has been active</em>. The seed is a 32 bit number, and since the granularity is in milliseconds, that's only a few weeks until it wraps around. But that's not the problem; the problem is: <strong>the time period in which you create that instance of <code>Random</code> is highly likely to be within a few minutes of the machine booting up.</strong> Every time you power-cycle a machine, or bring a new machine online in a cluster, there is a small window in which instances of Random are created, and the more that happens, the greater the odds are that you'll get a seed that you had before.</p> <p>As other have said: if you want a primary key for your database then <em>have the database generate you a primary key</em>; let the database do its job. If you want a globally unique identifier then <strong>use a guid</strong>; that's what they're for.</p> <p>And finally, if you are interested in learning more about the uses and abuses of guids then you might want to read my "guid guide" series; part one is here:</p> <p><a href="http://blogs.msdn.com/b/ericlippert/archive/2012/04/24/guid-guide-part-one.aspx">http://blogs.msdn.com/b/ericlippert/archive/2012/04/24/guid-guide-part-one.aspx</a></p>
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    1. POGuid.NewGuid() VS a random string generator from Random.Next()
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    1. USEric Lippert
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    1. COThanks for your answer, the guid guide was useful and your speculations in [part 3](http://blogs.msdn.com/b/ericlippert/archive/2012/05/07/guid-guide-part-three.aspx) lead us to generate our own ID's and session tokens using `RNGCryptoServiceProvider` rather than `NewGuid()`. See my own answer to this question below for details.
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      1. USGeorge Powell
    2. CO+1 for lying, then admitting you lied.
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