[Spread-users] Question About View ID / group_id

Ryan Caudy rcaudy at gmail.com
Tue Aug 30 18:42:33 EDT 2005

Your above guess is incorrect, Nilo.

The group ID consists of a memb_id, and an index.

The memb_id reflects the IP address (proc_id) of the configuration
leader at the time it is selected, as well as a UTC timestamp (with
some fudging to avoid repeats if IDs are generated rapidly) taken at
that host.  The memb_id component of the group_id is changed whenever
a heavyweight membership change affects the group.

The index is incremented with each lightweight membership change.

Hence, in a configuration without IP address or clock changes, there's
no danger of a repeat in the same or different partitions.


On 8/30/05, Nilo Rivera <nrivera at cs.jhu.edu> wrote:
> Hi,
> I wonder if someone could explain me how the group_id actually works, and
> how unique is it.  If servers start in a partitioned network, my
> guess is that a common group could have the same or different group_id in
> disconnected sites of the partition, and for each membership change,
> the new group_id equals the largest in the new membership plus one.  I
> noticed is 12 bytes long, so I wonder what additional information is it
> really stored there (or if my guess above is incorrect).
> Thanks,
> Nilo
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