On Aug 30, 2013, at 4:35 , Esteban Lorenzano <esteba...@gmail.com> wrote:
> > On Aug 29, 2013, at 5:08 PM, Sven Van Caekenberghe <s...@stfx.eu> wrote: > >> >> On 29 Aug 2013, at 16:51, Esteban Lorenzano <esteba...@gmail.com> wrote: >> >>> hi >>> >>> well... I've never been happy on using the UUID generator for my keys, but >>> is the fastest option I found. >>> There are, of course, alternatives: >>> >>> 1) Using your own number generator (sequential, or whatever). Problem with >>> that is that is image based, then you need a persistence strategy... then >>> you are slow. >>> 2) then you can use your own procedure in mongo... with same problem than >>> (1) >>> 3) you could use timestamp. but TimeStamps are slow :( >>> >>> anyway... I open to ideas :) >>> >>> in the mean time, you can check if your UUID generator is using the >>> primitive or not. In you are not, you have more possibilities of having a >>> collision. >> >> Yes, the Smalltalk code (type 4 UUID) is just a random number that is >> computed in a complex way. >> >> What does the primitive actually do ? Is it different ? > > the primitive uses the clock ticks to produce an UUID... you shouldn't have > repeated numbers that way... but well, it depends on the platform > implementation also. Wait, which primitive is this? UUID > primMakeUUID? That code calls libUUID, which (as long as it doesn't crash :P) fetches from dev/urandom (or the windows equivalent RtlGenRandom), there shouldn't ever be a problem getting duplicate results unless those system-provided resources are bugged, in which case your entire system is borked. The fallback code using UUIDGenerator default admittedly has a weak PRNG, and is dog slow: gen := UUIDGenerator new. [gen generateFieldsVersion4] bench '12,900 per second.' [ UUID new ] bench '3,610,000 per second.' "Primitive working, btw" but that hardly means you should run into duplicate sequential UUID's… The *only* way sequentially equal UUID's could arise, is if one uses UUIDGenerator directly, and creates a new instance each time, which does indeed run the risk of returning values derived from the same Time initialization , but that should *never* be done… Cheers, Henry
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