> On Jan 23, 2015, at 5:32 PM, Hristo Asenov <hristo.s.ase...@gmail.com> wrote:
>
> Hello everyone,
>
> I have noticed that in latest documentation on Riak data types
> (http://docs.basho.com/riak/latest/theory/concepts/crdts/#Counters
> <http://docs.basho.com/riak/latest/theory/concepts/crdts/#Counters>), for
> Counters it is not recommended to use them for ordered IDs (UUIDs). Can I
> implement g-counters (as described in the CRDT paper) using Riak’s Set
> datatype? I am wondering whether that will work out well for my use case.
>
> What I would like to do is to have synchronization of sequence numbers
> between multiple src processes that send their inputs to a single centralized
> process. I want all the sequence numbers to be unique so that the centralized
> process can create an ordering of the input messages based on the sequence
> numbers. Thus I would have an integer entry for each src process in the set,
> and the sum of all the integers would be my unique id. After the src process
> writes a value to the DHT for its corresponding entry, would it then have to
> read the value from the DHT in order to make sure it got committed without
> conflicts?
Hi Hristo,
I’m not sure if I completely followed your use case, but I believe that you
probably want strongly consistent operations if you want to generate a total
order over a series of operations.
Using the sum of the integers of a G-Counter (or a G-Counter built on Riak’s
set data structure) does not guarantee a globally unique number; given these
counters are designed (and therefore allowed) to diverge, imagine the following
scenario, possible due to delays in replication:
Replica A, G-Counter:
[{pid1, 2}, {pid2, 1}], Sum: 3
Replica B, G-Counter:
[{pid1, 1}, {pid2, 2}], Sum: 3
These both share the same sum, but should represent unique operations, right?
Did I understand correctly?
Thanks,
- Chris
Christopher Meiklejohn
Senior Software Engineer
Basho Technologies, Inc.
cmeiklej...@basho.com_______________________________________________
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