Re: UUIDs in core WAS: 9.4 Proposal: Initdb creates a single table
| От | Christopher Browne |
|---|---|
| Тема | Re: UUIDs in core WAS: 9.4 Proposal: Initdb creates a single table |
| Дата | |
| Msg-id | CAFNqd5UtzUqng2+7RgGzB8+UgB+039ndC-vnUNE2YLsjw3gEyA@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: UUIDs in core WAS: 9.4 Proposal: Initdb creates a single table (Marti Raudsepp <marti@juffo.org>) |
| Список | pgsql-hackers |
On Thu, Apr 24, 2014 at 8:43 PM, Marti Raudsepp <marti@juffo.org> wrote:
Cryptography is *hard*; treating it as certainty that things will be gotten correct
--
When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"
On Fri, Apr 25, 2014 at 3:36 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:Obviously you can't use random(). That's why I talked about
> Of course, the weak spot in this analysis is the assumption that there
> are actually 122 independent bits in the value. It's not difficult to
> imagine that systems with crummy random() implementations might only have
> something like 32 bits worth of real randomness.
cryptographic PRNGs, crypto libraries do proper seeding and generate
reliably random numbers all the time.
... And we can't be certain that there won't be some internal characteristic weakness.
Cryptography is *hard*; treating it as certainty that things will be gotten correct
tends to be a foolish assumption.
Which is why UUID "type 1" resolves this by combining multiple sorts of
anti-correlations, the combination of:
a) Node-specific information (e.g. - in the standard form, parts of the MAC address), so no collisions between node A and node B.
b) Timestamp, so that things that happen at different times will be kept unique.
c) An extra sequence, so that if there are multiple events on the same node at the same time, they *still* don't collide.
I trust the combination to work pretty well, and that's why it was designed that way.
A RNG, however good, can't provide the same guarantees of lack of conflicts.
When confronted by a difficult problem, solve it by reducing it to the
question, "How would the Lone Ranger handle this?"
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