Not so random Randomizer
-
@Jaime said:
Absolutely. But, if you are calling something called GenerateGUID and it happens to create a version 4 UUID, you will get back a random number that is suitable as a primary key in a distributed system. If you call something called tools.Randomizer.getNumber and use it as a primary key, you are an idiot. GUID are designed to be collision resistant, either through algorithm or keyspace. Random numbers as a class are not. Pointing out that there exist a subset of random numbers (version 4 UUIDs) that are collision resistant does little to make that false. One counter-example is not sufficient.
I don't think anyone argued that all random numbers are suitable as collision-resistant keys. As I read it, the original argument was whether a random number with a suitably large keyspace could generated collision-resistant keys and it appears it is.
-
@morbiuswilters said:
I don't think anyone argued that all random numbers are suitable as collision-resistant keys. As I read it, the original argument was whether a random number with a suitably large keyspace could generated collision-resistant keys and it appears it is.
Precisely. A 128-bit random number should not have collisions in an application space. This is not to say that i would ever USE a RNG for a primary key.
-
@morbiuswilters said:
I don't think anyone argued that all random numbers are suitable as collision-resistant keys. As I read it, the original argument was whether a random number with a suitably large keyspace could generated collision-resistant keys and it appears it is.
@Original Argument said:
Back to the OP.... somebody used a random number generator for primary keys and you call the implementation the WTF? Only a bad implementation would ever survive load testing; the concept is TRWTF.
@First Rebuttal said:
How much load do you do in your load testing that any randum number generator would fail? Using a trillion GUIDs gives you about 40 billionths of a percent chance of collision.
The original argument was whether the concept of using a random number as a PK is sane, which was countered by stating that a subset of random numbers are a perfectly acceptable as keys. Nobody has disagreed that a suitably large random number would work, but I have repeatedly pointed out that it simply doesn't matter because I never ever said that it was impossible to do, just generally a bad idea. Repeating the same thing over and over and providing more evidence of the validity of the exception case doesn't address the original point. A single exception does not invalidate a generality. Besides, the case presented here isn't a GUID, so the exceptional case isn't even on topic. The function in the OP returns a value of type "Number" which in ActionScript only has a maximum of 52 bits of precision. Birthday Paradox math says that the best implementation would have an unacceptable chance of collisions at around a million keys.
-
You also went on to say that@Jaime said:
I stand by my statement that anything that would be good at avoiding collisions would be a poor implementation of a general purpose random number generator.
Since you don't need something to avoid collisions in a large number space...
-
@Sutherlands said:
Apparently our definitions of "general purpose" differ. Numbers with a lot of bits are unweildy in most languages. Start with a version 4 UUID and use it to simulate a dice roll; it's much harder than it needs to be.You also went on to say that@Jaime said:
I stand by my statement that anything that would be good at avoiding collisions would be a poor implementation of a general purpose random number generator.
Since you don't need something to avoid collisions in a large number space...
-
@Jaime said:
@Sutherlands said:
You also went on to say that
@Jaime said:I stand by my statement that anything that would be good at avoiding collisions would be a poor implementation of a general purpose random number generator.
Since you don't need something to avoid collisions in a large number space...
Apparently our definitions of "general purpose" differ. Numbers with a lot of bits are unweildy in most languages. Start with a version 4 UUID and use it to simulate a dice roll; it's much harder than it needs to be.I guess, although using those UUIDs reminds me of the random number tables in, e.g., old CRC books. It's more difficult to use for a particular purpose, I suppose (like rolling a particular die), but it would probably be better as a general purpose RNG than whatever you'd use for your die rolls, since you ought to be able to adapt it pretty easily to just about anything.
