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Re^2: Generate a unique ID

by BrowserUk (Pope)
on Nov 15, 2010 at 12:13 UTC ( #871453=note: print w/replies, xml ) Need Help??


in reply to Re: Generate a unique ID
in thread Generate a unique ID

It's probably not relevant, but we have seen time "run backwards" on multi-core systems using AMD processors.

Was this using Time::HiRes on a Windows system? If so, I know how that can happen, and I don't think it is constrained to AMD processors, though I seem to remember seeing that Intel have addressed the underlying problem on their latest chips.

For my purposes, I'll be probably be using a time value limited to milliseconds anyway, but thanks for the heads up.


Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

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Re^3: Generate a unique ID
by GrandFather (Sage) on Nov 15, 2010 at 19:00 UTC

    It was actually in a C++ application using the high res 'multi media' timer (IIRC) in an application trying to sync clocks on external hardware. The information we found on the web implicated just AMD processors and was consistent with our observations, albeit with a fairly small sample set. I wasn't directly involved with the problem so I don't remember the details, but it was within the last two months and the computers involved were probably less than a year old.

    True laziness is hard work

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[hippo]: Make it an option?
[Corion]: hippo: Yes, but I'm not sure that it's even worth the effort of implementing it at all...
[Corion]: You'll only ever need that option if you have a long-running query whose results are not cached by your DB already, and in those cases I presume that the programmer will want to maintain the temporary tables themselves - I wouldn't know when to drop ...
[Corion]: ... the temporary tables, and also don't have a good idea on how to create unique table names for them
[hippo]: OIC. In that case leave it out but invite feature requests and see if any of the users suggest it. :-)

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