Developing with Riak KV
Data Types

Riak KV has Riak-specific data types based on convergent replicated data types (CRDTs). While Riak KV was built as a data-agnostic key/value store, Riak data types enable you to use Riak KV as a data-aware system and perform transactions on 6 CRDT-inspired data types:

Riak KV also has 1 context-free data type, that has similar usage but does not require contexts.

Counters, sets, gsets, maps, and hyperloglogs can be used as bucket-level data types or types that you interact with directly. Flags and registers must be embedded in maps.

For more information on how CRDTs work in Riak KV see Concepts: Data Types.

Getting Started with Riak Data Types

The following section explains how to set up a bucket that uses Riak data types. To get started using Riak data types:

  1. Create a bucket with the datatype parameter set.
  2. Confirm the bucket was properly configured.
  3. Activate the bucket type.

Creating a Bucket with a Riak Data Type

First create a bucket type that sets the datatype bucket parameter to either counter, map, set, or hll.

The following would create a separate bucket type for each of the four bucket-level data types:

riak admin bucket-type create maps '{"props":{"datatype":"map"}}'
riak admin bucket-type create sets '{"props":{"datatype":"set"}}'
riak admin bucket-type create counters '{"props":{"datatype":"counter"}}'
riak admin bucket-type create hlls  '{"props":{"datatype":"hll"}}'
riak admin bucket-type create gsets '{"props":{"datatype":"gset"}}'

Note

The names maps, sets, counters, hlls and gsets are not reserved terms. You are free to name bucket types whatever you like, with the exception of default.

Confirm Bucket configuration

Once you’ve created a bucket with a Riak data type, you can check to make sure that the bucket property configuration associated with that type is correct. This can be done through the riak admin interface:

riak admin bucket-type status maps

This will return a list of bucket properties and their associated values in the form of property: value. If our maps bucket type has been set properly, we should see the following pair in our console output:

datatype: map

Activate Bucket type

If a bucket type has been properly constructed, it needs to be activated to be usable in Riak. This can also be done using the bucket-type command interface:

riak admin bucket-type activate maps

To check whether activation has been successful, simply use the same bucket-type status command shown above.

See the Usage Examples section for further information on using Riak data types in the context of an application.

Required Bucket Properties

In order for Riak data types to work the bucket should have the following bucket properties:

  • allow_mult = true
  • last_write_wins = false

These settings are set by default and should not be changed.

Data Types and Context

Data type context is similar to causal context: it tells Riak KV which version of the data type a client is attempting to modify. Context is required by Riak KV when making decisions about convergence.

If no context is given when attempting a remove or remove-like operation, the operation may fail (removing a field that is not present) or succeed and remove more than intended (removing updates unseen by the client).

Note

The counter data type does not use context; Riak KV will return an empty value when the context is requested from a counter.

In the example below we’ll fetch the context from a user data map created for Ahmed:

// Using the "ahmedMap" Location from above:

FetchMap fetch = new FetchMap.Builder(ahmedMap).build();
FetchMap.Response response = client.execute(fetch);
Context ctx = response.getContext();
System.out.prinntln(ctx.getValue().toString())

// An indecipherable string of Unicode characters should then appear

bucket = client.bucket('users')
ahmed_map = Riak::Crdt::Map.new(bucket, 'ahmed_info', 'maps')
ahmed_map.instance_variable_get(:@context)

# => "\x83l\x00\x00\x00\x01h\x02m\x00\x00\x00\b#\t\xFE\xF9S\x95\xBD3a\x01j"

$map = (new \Basho\Riak\Command\Builder\FetchMap($riak))
    ->atLocation($location)
    ->build()
    ->execute()
    ->getMap();

echo $map->getContext(); // g2wAAAACaAJtAAAACLQFHUkv4m2IYQdoAm0AAAAIxVKxCy5pjMdhCWo=

bucket = client.bucket_type('maps').bucket('users')
ahmed_map = Map(bucket, 'ahmed_info')
ahmed_map.context

# g2wAAAABaAJtAAAACCMJ/vlTlb0zYQFq

// https://github.com/basho/riak-dotnet-client/blob/develop/src/RiakClientExamples/Dev/Using/DataTypes.cs

// Note: using a previous UpdateMap or FetchMap result
Console.WriteLine(format: "Context: {0}", args: Convert.ToBase64String(result.Context));

// Output:
// Context: g2wAAAACaAJtAAAACLQFHUkv4m2IYQdoAm0AAAAIxVKxCy5pjMdhCWo=

var options = {
    bucketType: 'maps',
    bucket: 'customers',
    key: 'ahmed_info'
};

client.fetchMap(options, function (err, rslt) {
    if (err) {
        throw new Error(err);
    }

    logger.info("context: '%s'", rslt.context.toString('base64'));
});

// Output:
// context: 'g2wAAAACaAJtAAAACLQFHUmjDf4EYTBoAm0AAAAIxVKxC6F1L2dhSWo='

%% You cannot fetch a data type's context directly using the Erlang
%% client. This is actually quite all right, as the client automatically
%% manages contexts when making updates.

Context with the Ruby, Python, and Erlang clients

In the Ruby, Python, and Erlang clients, you will not need to manually handle context when making data type updates. The clients will do it all for you. The one exception amongst the official clients is the Java client. We’ll explain how to use data type contexts with the Java client directly below.

Context with the Java and PHP Clients

With the Java and PHP clients, you’ll need to manually fetch and return data type contexts for the following operations:

  • Disabling a flag within a map
  • Removing an item from a set (whether the set is on its own or within a map)
  • Removing a field from a map

Without context, these operations simply will not succeed due to the convergence logic driving Riak data types. The example below shows you how to fetch a data type’s context and then pass it back to Riak. More specifically, we’ll remove the paid_account flag from the map:

// This example uses our "ahmedMap" location from above:

FetchMap fetch = new FetchMap.Builder(ahmedMap)
    .build();
FetchMap.Response response = client.execute(fetch);
Context ctx = response.getContext();
MapUpdate removePaidAccountField = new MapUpdate()
        .removeFlag("paid_account");
UpdateMap update = new UpdateMap.Builder(ahmedMap, removePaidAccountField)
        .withContext(ctx)
        .build();
client.execute(update);

$map = (new \Basho\Riak\Command\Builder\FetchMap($riak))
    ->atLocation($location)
    ->build()
    ->execute()
    ->getMap();

$updateSet = (new \Basho\Riak\Command\Builder\UpdateSet($riak))
    ->remove('opera');

(new \Basho\Riak\Command\Builder\UpdateMap($riak))
    ->updateSet('interests', $updateSet)
    ->atLocation($location)
    ->withContext($map->getContext())
    ->build()
    ->execute();

Usage Examples

The pages listed above detail using Riak data types at the application level using Basho’s officially supported Riak KV clients. For more on getting started with client libraries check out the Developing with Riak KV: Getting Started section.

All the examples use the bucket type names from above (counters, sets, and maps). You’re free to substitute your own bucket type names if you wish.