[EMAIL PROTECTED] wrote:
On Tue, Sep 19, 2006 at 11:21:51PM -0400, Alvaro Herrera wrote:
[EMAIL PROTECTED] wrote:
On Tue, Sep 19, 2006 at 08:20:13AM -0500, Jim C. Nasby wrote:
On Mon, Sep 18, 2006 at 07:45:07PM -0400, [EMAIL PROTECTED] wrote:
I would not use a 100% random number generator for a UUID value as was
suggested. I prefer inserting the MAC address and the time, to at
least allow me to control if a collision is possible. This is not easy
to do using a few lines of C code. I'd rather have a UUID type in core
with no generation routine, than no UUID type in core because the code
is too complicated to maintain, or not portable enough.
As others have mentioned, using MAC address doesn't remove the
possibility of a collision.
It does, as I control the MAC address.
What happens if you have two postmaster running on the same machine?
Could be bad things. :-)
For the case of two postmaster processes, I assume you mean two
different databases? If you never intend to merge the data between the
two databases, the problem is irrelevant. There is a much greater
chance that any UUID form is more unique, or can be guaranteed to be
unique, within a single application instance, than across all
application instances in existence. If you do intend to merge the
data, you may have a problem.
You may. But it's not very likely. Since a) there is a 13-bit random number in addition to
the MAC address (the clock sequence) and b) the timestamp has a granularity of 100 nanosec.
An implementation could be made to prevent clock-sequence collisions on the same machine and
thereby avoid this altogether.
Kind Regards,
Thomas Hallgren
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