As part of a new feature we are working on, we've run into a situation where it would be incredibly convenient to have a check-and-set (CAS) API for Riak KV. In short, we are trying to build a unique index of a bucket, using a second bucket which acts as a reverse index.
The CAS API would operate in the same manner as a PUT, except it should take a "last vclock". The new value + last vclock are submitted to the responsible vnodes. The vnodes respond if the last vclock for the key matches the specified last value. If we get "r" nodes responding that the last value matches, then we should commit the write. This method is basically a two-phase commit. It would also be great if no-value sentinel could be specified to indicate the CAS should only succeed if there is not already a key. We need this to make sure uniqueness constraints are not violated. I wanted to gauge the interest from the community in something like this, and see if I could get thoughts from the Basho team on if this could be implemented. Best Regards, Armon Dadgar
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