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Python clients for Riak.

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README.rst

Python Client for Riak

Documentation

Documentation for the Riak Python Client Library is available here. The documentation source is found in docs/ subdirectory and can be built with Sphinx.

Documentation for Riak is available at http://wiki.basho.com/How-Things-Work.html

Install

The recommended version of Python for use with this client is Python 2.7.

You must have Protocol Buffers installed before you can install the Riak Client. From the Riak Python Client root directory, execute:

python setup.py install

There is an additional dependency on the Python package setuptools. Please install setuptools first, e.g. port install py27-setuptools for OS X and MacPorts.

Unit Test

To run the unit tests against a Riak server (with default TCP port configuration) on localhost, execute:

python setup.py test

If you don't have Luwak or Riak Search enabled you can set the SKIP_LUWAK and SKIP_SEARCH environment variables to skip those tests.

If your Riak server isn't running on localhost, use the environment variables RIAK_TEST_HOST and RIAK_TEST_HTTP_PORT and RIAK_TEST_PB_PORT=8087 to specify where to find the Riak server.

Tutorial

This tutorial assumes basic working knowledge of how Riak works & what it can do. If you need a more comprehensive overview how to use Riak, please check out the Riak Fast Track.

Quick Start

For the impatient, simple usage of the official Python binding for Riak looks like:

import riak

# Connect to Riak.
client = riak.RiakClient()

# Choose the bucket to store data in.
bucket = client.bucket('test')


# Supply a key to store data under.
# The ``data`` can be any data Python's ``json`` encoder can handle.
person = bucket.new('riak_developer_1', data={
    'name': 'John Smith',
    'age': 28,
    'company': 'Mr. Startup!',
})
# Save the object to Riak.
person.store()

Connecting To Riak

There are two supported ways to connect to Riak, the HTTP interface & the Protocol Buffers interface. Both provide the same API & full access to Riak.

The HTTP interface is easier to setup & is well suited for development use. It is the slower of the two interfaces, but if you are only making a handful of requests, it is more than capable.

The Protocol Buffers (also called protobuf) is more difficult to setup but is significantly faster (2-3x) and is more suitable for production use. This interface is better suited to a higher number of requests.

To use the HTTP interface and connecting to a local Riak on the default port, no arguments are needed:

import riak

client = riak.RiakClient()

The constructor also configuration options such as host, port & prefix. Please refer to the :doc:`client` documentation for full details.

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To use the Protocol Buffers interface:

import riak

client = riak.RiakClient(port=8087, transport_class=riak.RiakPbcTransport)

The transport_class argument indicates to the client which backend to use. We didn't need to specify it in the HTTP example because riak.RiakHttpTransport is the default class.

Using Buckets

Buckets in Riak's terminology are segmented keyspaces. They are a way to categorize different types of data and are roughly analogous to tables in an RDBMS.

Once you have a client, selecting a bucket is simple. Provide a string of the name of the bucket to use:

test_bucket = client.bucket('test')

If the bucket does not exist, Riak will create it for you. You can also open as many buckets as you need:

user_bucket = client.bucket('user')
profile_bucket = client.bucket('profile')
status_bucket = client.bucket('status')

If needed, you can also manually instantiate a bucket like so:

user_bucket = riak.RiakBucket(client, 'user')

The buckets themselves provide many different methods. The most commonly used are:

  • get - Fetches a key's value (decoded from JSON).
  • get_binary - Also fetches a key's raw value (plain text or binary).
  • new - Creates a new key/value pair (encoded in JSON).
  • new_binary - Creates a new key/raw value pair.

See the full :doc:`bucket` documentation for the other methods.

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Storing Keys/Values

Once you've got a working client/bucket, the next task at hand is storing data. Riak provides several ways to store your data, but the most common are a JSON-encoded structure or a binary blob.

To store JSON-encoded data, you'd do something like the following:

import riak

client = riak.RiakClient()
user_bucket = client.bucket('user')

# We're creating the user data & keying off their username.
new_user = user_bucket.new('johndoe', data={
    'first_name': 'John',
    'last_name': 'Doe',
    'gender': 'm',
    'website': 'http://example.com/',
    'is_active': True,
})
# Note that the user hasn't been stored in Riak yet.
new_user.store()

Note that any data Python's json (or simplejson) encoder can handle is fair game.

As mentioned, Riak can also handle binary data, such as images, audio files, etc. Storing binary data looks almost identical:

import riak

client = riak.RiakClient()
user_photo_bucket = client.bucket('user_photo')

# For example purposes, we'll read a file off the filesystem, but you can get
# the data from anywhere.
the_photo_data = open('/tmp/johndoe_headshot.jpg', 'rb').read()

# We're storing the photo in a different bucket but keyed off the same
# username.
new_user = user_photo_bucket.new_binary('johndoe', data=the_photo_data, content_type='image/jpeg')
new_user.store()

You can also manually store data by using RiakObject:

import riak
import time
import uuid

client = riak.RiakClient()
status_bucket = client.bucket('status')

# We use ``uuid.uuid1().hex`` here to create a unique identifier for the status.
post_uuid = uuid.uuid1().hex
new_status = riak.RiakObject(client, status_bucket, post_uuid)

# Add in the data you want to store.
new_status.set_data({
    'message': 'First post!',
    'created': time.time(),
    'is_public': True,
})

# Set the content type.
new_status.set_content_type('application/json')

# We want to do JSON-encoding on the value.
new_status._encode_data = True

# Again, make sure you save it.
new_status.store()

Getting Single Values Out

Storing data is all well and good, but you'll need to get that data out at a later date.

Riak provides several ways to get data out, though fetching single key/value pairs is the easiest. Just like storing the data, you can pull the data out in either the JSON-decoded form or a binary blob. Getting the JSON-decoded data out looks like:

import riak

client = riak.RiakClient()
user_bucket = client.bucket('user')

johndoe = user_bucket.get('johndoe')

# You've now got a ``RiakObject``. To get at the values in a dictionary
# form, call:
johndoe_dict = johndoe.get_data()

Getting binary data out looks like:

import riak

client = riak.RiakClient()
user_photo_bucket = client.bucket('user_photo')

johndoe = user_photo_bucket.get_binary('johndoe')

# You've now got a ``RiakObject``. To get at the binary data, call:
johndoe_headshot = johndoe.get_data()

Manually fetching data is also possible:

import riak

client = riak.RiakClient()
status_bucket = client.bucket('status')

# We're using the UUID generated from the above section.
first_post_status = riak.RiakObject(client, status_bucket, post_uuid)
first_post_status._encode_data = True
r = status_bucket.get_r()

# Calling ``reload`` will cause the ``RiakObject`` instance to load fresh
# data/metadata from Riak.
first_post_status.reload(r)

# Finally, pull out the data.
message = first_post_status.get_data()['message']

Fetching Data Via Map/Reduce

When you need to work with larger sets of data, one of the tools at your disposal is MapReduce. This technique iterates over all of the data, returning data from the map phase & combining all the different maps in the reduce phase(s).

To perform a map operation, such as returning all active users, you can do something like:

import riak

client = riak.RiakClient()
# First, you need to ``add`` the bucket you want to MapReduce on.
query = client.add('user')
# Then, you supply a Javascript map function as the code to be executed.
query.map("function(v) { var data = JSON.parse(v.values[0].data); if(data.is_active == true) { return [[v.key, data]]; } return []; }")

for result in query.run():
    # Print the key (``v.key``) and the value for that key (``data``).
    print "%s - %s" % (result[0], result[1])

# Results in something like:
#
# mr_smith - {'first_name': 'Mister', 'last_name': 'Smith', 'is_active': True}
# johndoe - {'first_name': 'John', 'last_name': 'Doe', 'is_active': True}
# annabody - {'first_name': 'Anna', 'last_name': 'Body', 'is_active': True}

You can also do this manually:

import riak

client = riak.RiakClient()
query = riak.RiakMapReduce(client).add('user')
query.map("function(v) { var data = JSON.parse(v.values[0].data); if(data.is_active == true) { return [[v.key, data]]; } return []; }")

for result in query.run():
    print "%s - %s" % (result[0], result[1])

Adding a reduce phase, say to sort by username (key), looks almost identical:

import riak

client = riak.RiakClient()
query = client.add('user')
query.map("function(v) { var data = JSON.parse(v.values[0].data); if(data.is_active == true) { return [[v.key, data]]; } return []; }")
query.reduce("function(values) { return values.sort(); }")

for result in query.run():
    # Print the key (``v.key``) and the value for that key (``data``).
    print "%s - %s" % (result[0], result[1])

# Results in something like:
#
# annabody - {'first_name': 'Anna', 'last_name': 'Body', 'is_active': True}
# johndoe - {'first_name': 'John', 'last_name': 'Doe', 'is_active': True}
# mr_smith - {'first_name': 'Mister', 'last_name': 'Smith', 'is_active': True}

Working With Related Data Via Links

Links are powerful concept in Riak that allow, within the key/value pair's metadata, relations between objects.

Adding them to your data is relatively trivial. For instance, we'll link a user's statuses to their user data:

import riak
import uuid

client = riak.RiakClient()
user_bucket = client.bucket('user')
status_bucket = client.bucket('status')

johndoe = user_bucket.get('johndoe')

new_status = status_bucket.new(uuid.uuid1().hex, data={
    'message': 'First post!',
    'created': time.time(),
    'is_public': True,
})
# Add one direction (from status to user)...
new_status.add_link(johndoe)
new_status.store()

# ... Then add the other direction.
johndoe.add_link(new_status)
johndoe.store()

Fetching the data is equally simple:

import riak

client = riak.RiakClient()
user_bucket = client.bucket('user')

johndoe = user_bucket.get('johndoe')

for status_link in johndoe.get_links():
    # Since what we get back are lightweight ``RiakLink`` objects, we need to
    # get the associated ``RiakObject`` to access its data.
    status = status_link.get()
    print status.get_data()['message']

Using Search

Riak Search is a new feature available as of Riak 0.13. It allows you to create queries that filter on data in the values without writing a MapReduce. It takes inspiration from Lucene, a popular Java-based search library, and incorporates a Solr-like interface into Riak. The setup of this is outside the realm of this tutorial, but usage of this feature looks like:

import riak

client = riak.RiakClient()

# First parameter is the bucket we want to search within, the second
# is the query we want to perform.
search_query = client.search('user', 'first_name:[Anna TO John]')

for result in search_query.run():
    # You get ``RiakLink`` objects back.
    user = result.get()
    user_data = user.get_data()
    print "%s %s" % (user_data['first_name'], user_data['last_name'])

# Results in something like:
#
# John Doe
# Anna Body

You can enable and disable search for specific buckets through convenience methods that install/remove the precommit hook

bucket = client.bucket('search')

if bucket.search_enabled():
bucket.disable_search()
else:
bucket.enable_search()

Search using the Solr Interface

The search as outlined above goes through Riak's MapReduce facilities to find and fetch objects. Sometimes you either want to go through the Solr-like interface Riak Search offers, e.g. to index and search documents without storing them in Riak KV and relying on the pre-commit hook to index.

Using the Solr interface also allows you to specify sort and limit parameters, which, using the search based on MapReduce, you'd have to do that with reduce functions.

You can index documents into search indexes as simple Python dicts, which need to have an attribute named "id":

client = riak.RiakClient()
client.solr().add("user", {"id": "anna", "first_name": "Anna"})

To search for documents, specify the index and a query string:

client = riak.RiakClient()
client.solr().search("user", "first_name:Anna")

Additionally you can specify all the parameters supported by the Solr interface:

client.solr().search("user", "Anna", wt="json", df="first_name")

The search interface supports both XML and JSON, parsing both result formats into dicts.

You can also remove documents from the index again, using either a list of document ids or queries:

client.solr().delete("user", docs=["anna"], queries=["first_name:Anna"])

Using Key Filters

Key filters are a new feature available as of Riak 0.14. They are a way to pre-process MapReduce inputs from a full bucket query simply by examining the key — without loading the object first. This is especially useful if your keys are composed of domain-specific information that can be analyzed at query-time.

To illustrate this, let’s contrive an example. Let’s say we’re storing customer invoices with a key constructed from the customer name and the date, in a bucket called “invoices”. Here are some sample keys:

basho-20101215
google-20110103
yahoo-20090613

To query all invoices for a given customer:

import riak

client = riak.RiakClient()

query = client.add("invoices")
query.add_key_filter("tokenize", "-", 1)
query.add_key_filter("eq", "google")

query.map("""function(v) {
    var data = JSON.parse(v.values[0].data);
    return [[v.key, data]];
}""")

Alternatively, you can use riak.key_filter to build key filters:

query.add_key_filters(key_filter.tokenize("-", 1).eq("google"))

Boolean operators can be used with riak.f instances:

# Query basho's orders for 2010
filters = key_filter.tokenize("-", 1).eq("basho")\
        & key_filter.tokenize("-", 2).starts_with("2010")

Filters can be combined using the + operator to produce very complex filters:

# Query invoices for basho or google
filters = key_filter.tokenize("-", 1) + (key_filter.eq("basho") | key_filter.eq("google"))

# This is the same as the following key filters
[['tokenize', '-', 1], ['or', [['eq', 'google']], [['eq', 'yahoo']]]]

Test Server

The client includes a Riak test server that can be used to start a Riak instance on demand for testing purposes in your application. It uses in-memory storage backends for both Riak KV and Riak Search and is therefore reasonably fast for a testing setup. The in-memory setups also make it easier to wipe all data in the instance without having to list and delete all keys manually. The original code comes from Ripple, as do the file system implementations.

The server needs a local Riak installation, of which it uses only the installed Erlang libraries and the configuration files to generate and run a temporary server in a different directory. Make sure you run the most recent stable version of Riak, and not a development snapshot, where your mileage may vary.

By default, the HTTP port is set to 9000 and the Protocol Buffers interface listens on port 9001.

To use it, simply point it to your local Riak installation, and the rest is done automagically:

from riak.test_server import TestServer

server = TestServer(bin_dir="/usr/local/riak/0.14.2/bin")
server.prepare()
server.start()

The server is started as an external process, with communication going through the Erlang console. That allows it to easily wipe the in-memory backends used by Riak and Riak Search. You can use the recycle() method to clean up the server:

server.recycle()

To change the default configuration, you can specify additional arguments for the Erlang VM. Let's raise the maximum number of processes to 1000000, just for fun:

server = TestServer(vm_args={"+P": "1000000"})

You can also change the default configuration used to generate the app.config file for the Riak instance. The format of the attributes follows the convention of the app.config file itself, using a dict with keys for every section in the configuration file, so "riak_core", "riak_kv", and so on. These in turn are also dicts, following the same key-value format of the app.config file.

So to change the default HTTP port to 8080, you can do the following:

server = TestServer(riak_core={"web_port": 8080})

The server should shut down properly when you stop the Python process, but if you only need it for a subset of your tests, just stop the server:

server.stop()

If you plan on repeatedly running the test server, either in multiple test suites or in subsequent test runs, be sure to call cleanup() before starting or after stopping it.

Luwak for Large File Storage

If your Riak installation has Luwak support enabled, you can use the client to interact with it, storing, fetching and deleting files. Note that Luwak is HTTP only and will always use the settings provided for the HTTP transport. If you mix Luwak with normal Riak usage through the Protocol Buffers interface, it's best to use multiple client objects for each separate use case:

client = riak.RiakClient()

image = open('hulk.jpg', 'rb')
client.store_file('image.jpg', image.read(), content_type="image/jpeg")

# Returns just the data stored in luwak
client.get_file('image.jpg')

client.delete_file('image.jpg')
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