Hi all -
I'm not sure whether this has been discussed here before, but I've at
times felt that Riak - while having a great way of supporting resolution
of write conflicts - is missing a good way of *detecting* such conflicts.
(Unless of course some feature has been added which I have missed...)
And recently, when trying to reason about whether our Riak-based
algorithm gave the guarantees it was supposed to, and what to do about
it when it didn't, one of the conclusions was "either this goes well, or
else we get a conflict, in which case all is well if we find and handle
that conflict in a timely manner".
Now, I'm as much for periodic jobs reviewing nontrivial parts of the
database as the next man (and also fudge factors such as "upper bound on
consistency delay"), but I think we can do better. :-)
Thus, I give to you, for your consideration and discussion, a mechanism
for indexing conflicts in 2i as they arise:
https://github.com/trifork/riak_kv/tree/sibling_index
I think 2i is a quite appropriate vehicle for this. The implementation
doesn't have much rocket science in it, either. As for the special names
involved (and the extent to which the mechanism should be configurable),
I'll leave that to the naming (and configurability) experts.
As far as I know, the code would also handle conflicts created at
replication time.
Enough talk - demo time:
# First, setup bucket to support conflicts:
$ curl -XPUT -H'content-type: application/json' -d'{"props":
{"allow_mult": true}}' http://localhost:8098/buckets/somebucket/props
# Create an object, marking it as something we'd like to monitor for
siblings:
$ curl -XPUT -d'Value 1' -H'X-Riak-Meta-X-Index-Siblings: true'
http://localhost:8098/buckets/somebucket/keys/thekey
# Then create a conflict:
$ curl -XPUT -d'Value 2'
http://localhost:8098/buckets/somebucket/keys/thekey
# Are there any conflicts?
$ curl -XGET
http://localhost:8098/buckets/somebucket/index/x_riak_siblings_int/0/999999
{"keys":["thekey"]}
# The value of the index is the number of siblings.
$ curl -XGET
http://localhost:8098/buckets/somebucket/index/x_riak_siblings_int/2/2
{"keys":["thekey"]}
What do you think?
Regards,
Erik Søe Sørensen
--
Mobile: + 45 26 36 17 55 | Skype: eriksoesorensen | Twitter: @eriksoe
Trifork A/S | Margrethepladsen 4 | DK-8000 Aarhus C |
www.trifork.com <http://www.trifork.com/>
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