Values & Objects

Keys in Riak are namespaced into buckets, and their associated values are represented by objects, not to be confused with Python “objects”. A RiakObject is a container for the key, the Vector clock, the value(s) and any metadata associated with the value(s).

Values may also be datatypes, but are not discussed here.


Vector clock

Vector clocks are Riak’s means of tracking the relationships between writes to a key. It is best practice to fetch the latest version of a key before attempting to modify or overwrite the value; if you do not, you may create Siblings or lose data! The content of a vector clock is essentially opaque to the user.


Fetching, storing, and deleting keys are the bread-and-butter of Riak.

Value and Metadata

Unless you have enabled Siblings via the allow_mult bucket property, you can inspect and manipulate the value and metadata of an object directly using these properties and methods:


Because Riak’s consistency model is “eventual” (and not linearizable), there is no way for it to disambiguate writes that happen concurrently. The Vector clock helps establish a “happens after” relationships so that concurrent writes can be detected, but with the exception of Data Types, Riak has no way to determine which write has the correct value.

Instead, when allow_mult is True, Riak keeps all writes that appear to be concurrent. Thus, the contents of a key’s value may, in fact, be multiple values, which are called “siblings”. Siblings are modeled in RiakContent objects, which contain all of the same Value and Metadata methods and attributes as the parent object.

You do not typically have to create RiakContent objects yourself, but they will be created for you when fetching objects from Riak.


The Value and Metadata accessors on RiakObject are actually proxied to the first sibling when the object has only one.

Conflicts and Resolvers

When an object is not in conflict, it has only one sibling. When it is in conflict, you will have to resolve the conflict before it can be written again. How you choose to resolve the conflict is up to you, but you can automate the process using a resolver function.

If you do not supply a resolver function, or your resolver leaves multiple siblings present, accessing the Value and Metadata will result in a ConflictError being raised.