On 29/12/09 19:29 +0100, Mathias Behrle wrote: > * Betr.: " [tryton-dev] Adding random unique sequence" (Tue, 29 Dec 2009 > 18:38:50 +0100): > > > I would like to add a new type of sequence in Tryton that will generate > > random > > but unique number. > > For what is it needed? > > > A simple solution will be to generate random number and compare it with > > already generated number (stored in a table). But there is the birthday > > paradox [1] that reduces the speed of this method. > > Birthday paradox is strongly related to the limited quantity of available > numbers. > > I don't know, for what purpose it is needed. Does it have to be unique for > the machine, for the database, for the server, for universe? > Perhaps it would be possible to use something like the Message-ID for news, > that > also has to be unique. Combining a unique part with a random part could save a > lot of overhead. > > BTW: As soon as we will have Tryton work as a mail server it would be > desirable to have a (unique) domain anyway.
We can use UUID like it is already done in calendar modules. And normally, Tryton will not need to generate Message-ID as it is not intended to be a MTA. > > > An other way will be to store in a table every possible value (if the length > > of the number is fixed) and pick/remove one randomly. But here the > > generation > > of all values can be slow. > > Seems to me like a huge table which is a lot of overhead. And it won't be > random, if you know numbers taken already from this table. The randomness is for external people as I explain on previous email. -- Cédric Krier B2CK SPRL Rue de Rotterdam, 4 4000 Liège Belgium Tel: +32 472 54 46 59 Email: [email protected] Jabber: [email protected] Website: http://www.b2ck.com/ twitter: http://twitter.com/cedrickrier identi.ca: http://identi.ca/cedrickrier
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