>-----Original Message----- >From: Michael Dykman [mailto:mdyk...@gmail.com] >Sent: Friday, January 21, 2011 11:35 AM >To: Johan De Meersman >Cc: Anthony Pace; mysql. >Subject: Re: best way to have a unique key > >One of the components of the UUID is drawn form the mac address of the >server.. While in practice this is not true of all systems > >(except from http://dev.mysql.com/doc/refman/5.0/en/miscellaneous- >functions.html#function_uuid) > Currently, the MAC address of an interface is taken into >account only on FreeBSD and Linux. On other operating systems, MySQL >uses a randomly generated 48-bit number. >(end except) > >that potentially 48-bit random portion has 281474976710656 >possibilities, which makes in far, far more likely that your server is >hit by a meteor during a snowstorm in August while the Dalai Lama is >doing an Elvis impression for the Chinese premier. > [JS] Boy, if I had a nickel for every time I've heard that...
Seriously, though I've written and used enough pseudo-random number generators to have a tiny nagging doubt. I didn't realize that MySQL didn't use the MAC address on Windows platforms. Also, it is possible to programmatically change a MAC address (for system failover, for example). If you're not the kind of person who stays up nights worrying about proton decay, you're probably justified in shrugging this off. You'll likely be collecting your pension before anything nasty happens. > - michael dykman > >On Fri, Jan 21, 2011 at 1:22 AM, Johan De Meersman <vegiv...@tuxera.be> >wrote: >> I have to say, something similar was my first thought, too - you never >> mention uuid in your original post. As already stated, uuid() should be a >> Universal Unique IDentifier. It's afaik a random 128-bit number; given the >> space to choose from it should be rather unique. I have to admit that I'm >> not entirely confident about that myself, either, though: as Pratchett put >> it, one-in-a-million chances tend to pop up nine times out of ten. >> >> The code should have bits for handling duplicate primaries regardless of >> the >> method used to generate it, tough, so there's no reason to not do it. >> Having >> two subsequent UUID() calls generate pre-existing numbers seems to me to be >> likely in the same way as having Bush return his dirty oil dollars to Irak. >> >> On Thu, Jan 20, 2011 at 8:10 PM, Anthony Pace ><anthony.p...@utoronto.ca>wrote: >> >>> Dude, come on. I know that all primary keys have to be unique; however, I >>> was obviously referring to the use of uuid over auto incrementation. >>> >>> On 1/20/2011 1:36 PM, Michael Dykman wrote: >>> >>>> It is axiomatic in the relational model that a primary must be unique. >>>> This is not a quirk put forth by your current employer. Neither >>>> MySQL nor any other RDBMS will allow you to establish a primary key >>>> that is not unique. >>>> >>>> - michael dykman >>>> >>>> On Thu, Jan 20, 2011 at 1:32 PM, Anthony Pace<anthony.p...@utoronto.ca> >>>> wrote: >>>> >>>>> Due to certain reasons, the company I am doing business with has decided >>>>> that the primary key, for an orders table, be a unique key; however, I >>>>> don't >>>>> like the possibility of it conflicting if moved to another machine. >>>>> >>>>> What are some pitfalls of using a unique key, that is generated by a >>>>> server >>>>> side script, rather than by mysql? >>>>> What are the best ways to do this? >>>>> >>>>> Please keep in mind this variable will also be displayed on the >>>>> customer's >>>>> Receipt, but again, since it's random, it doesn't have to mean anything. >>>>> >>>>> -- >>>>> MySQL General Mailing List >>>>> For list archives: http://lists.mysql.com/mysql >>>>> To unsubscribe: http://lists.mysql.com/mysql?unsub=mdyk...@gmail.com >>>>> >>>>> >>>>> >>>> >>>> >>> >>> -- >>> MySQL General Mailing List >>> For list archives: http://lists.mysql.com/mysql >>> To unsubscribe: http://lists.mysql.com/mysql?unsub=vegiv...@tuxera.be >>> >>> >> >> >> -- >> Bier met grenadyn >> Is als mosterd by den wyn >> Sy die't drinkt, is eene kwezel >> Hy die't drinkt, is ras een ezel >> > > > >-- > - michael dykman > - mdyk...@gmail.com > > May the Source be with you. > >-- >MySQL General Mailing List >For list archives: http://lists.mysql.com/mysql >To unsubscribe: http://lists.mysql.com/mysql?unsub=je...@gii.co.jp -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/mysql?unsub=arch...@jab.org
