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As I was looking for a system to store documents at $work, Riak was
pointed to me by one of my coworkers. I'm looking for a solution of this
type to store various types of documents, from HTML pages to json. I
need a system that is distributed, faul tolerant, and that works with
Perl.
So Riak is a document based database, it's key value, no sql, REST, and
in Erlang. You can read more about it here or watch an introduction
here. Like <ahref="http://couchdb.apache.org/">CouchDB, Riak provides a
REST interface, so you don't have to write any Erlang code.
One of the nice things with Riak it's that it let you defined the N, R
and W value for each operation. This values are:
- N: the number of replicas of each value to store
- R: the number of replicas required to perform a read operation
- W: the number of replicas needed for a write operation
Riak comes with library for python ruby PHP and even javascript, but not
for Perl. As all these libraries are just communicating with Riak via
the REST interface, I've started to write one using AnyEvent::HTTP, and
also a backend for KiokuDB.
** Installing and using Riak
If you interested in Riak, you can install it easily. First, you will
need the Erlang VM. On debian, a simple
#+BEGIN_EXAMPLE
% sudo aptitude install erlang
#+END_EXAMPLE
install everything you need. Next step is to install Riak:
#+BEGIN_EXAMPLE
% wget http://hg.basho.com/riak/get/riak-0.6.2.tar.gz
% tar xzf riak-0.6.2.tar.gz
% cd riak
% make
% export RIAK=`pwd`
#+END_EXAMPLE
Now, you can start to use it with
#+BEGIN_EXAMPLE
% ./start-fresh config/riak-demo.erlenv
#+END_EXAMPLE
or if you want to test it in cluster mode, you can write a configuration
like this:
#+BEGIN_EXAMPLE
{cluster_name, "default"}.
{ring_state_dir, "priv/ringstate"}.
{ring_creation_size, 16}.
{gossip_interval, 60000}.
{storage_backend, riak_fs_backend}.
{riak_fs_backend_root, "/opt/data/riak/"}.
{riak_cookie, riak_demo_cookie}.
{riak_heart_command, "(cd $RIAK; ./start-restart.sh $RIAK/config/riak-demo.erlenv)"}.
{riak_nodename, riakdemo}.
{riak_hostname, "192.168.0.11"}.
{riak_web_ip, "192.168.0.11"}.
{riak_web_port, 8098}.
{jiak_name, "jiak"}.
{riak_web_logdir, "/tmp/riak_log"}.
#+END_EXAMPLE
Copy this config on a second server, edit it to replace the
riak\_hostname and riak\_nodename. On the first server, start it like
show previously, then on the second, with
#+BEGIN_EXAMPLE
% ./start-join.sh config/riak-demo.erlenv 192.168.0.11
#+END_EXAMPLE
where the IP address it the address of the first node in your cluster.
Let's check if everything works:
#+BEGIN_EXAMPLE
% curl -X PUT -H "Content-type: application/json" \
http://192.168.0.11:8098/jiak/blog/lumberjaph/ \
-d "{\"bucket\":\"blog\",\"key\":\"lumberjaph\",\"object\":{\"title\":\"I'm a lumberjaph, and I'm ok\"},\"links\":[]}"
% curl -i http://192.168.0.11:8098/jiak/blog/lumberjaph/
#+END_EXAMPLE
will output (with the HTTP blabla)
#+BEGIN_EXAMPLE
{"object":{"title":"I'm a lumberjaph, and I'm ok"},"vclock":"a85hYGBgzGDKBVIsbGubKzKYEhnzWBlCTs08wpcFAA==","lastmod":"Sun, 13 Dec 2009 20:28:04 GMT","vtag":"5YSzQ7sEdI3lABkEUFcgXy","bucket":"blog","key":"lumberjaph","links":[]}
#+END_EXAMPLE
** Using Riak with Perl and KiokuDB
I need to store various things in Riak: html pages, json data, and
objects using KiokuDB. I've started to write a client for Riak with
AnyEvent, so I can do simple operations at the moment, (listing
information about a bucket, defining a new bucket with a specific
schema, storing, retriving and deleting documents). To create a client,
you need to
#+BEGIN_SRC perl
my $client = AnyEvent::Riak->new(
host => 'http://127.0.0.1:8098',
path => 'jiak',
);
#+END_SRC
As Riak exposes to you it's N, R, and W value, you can also set them in
creation the client:
#+BEGIN_SRC perl
my $client = AnyEvent::Riak->new(
host => 'http://127.0.0.1:8098',
path => 'jiak',
r => 2,
w => 2,
dw => 2,
);
#+END_SRC
where:
- the W and DW values define that the request returns as soon as at
least W nodes have received the request, and at least DW nodes have
stored it in their storage backend.
- with the R value, the request returns as soon as R nodes have
responded with a value or an error. You can also set this values when
calling fetch, store and delete. By default, the value is set to 2.
So, if you wan to store a value, retrieve it, then delete it, you can
do:
#+BEGIN_SRC perl
my $store =
$client->store({bucket => 'foo', key => 'bar', object => {baz => 1},})
->recv;
my $fetch = $client->fetch('foo', 'bar')->recv;
my $delete = $client->delete('foo', 'bar')->recv;
#+END_SRC
If there is an error, the croak method from AnyEvent is used, so you may
prefer to do this:
#+BEGIN_SRC perl
use Try::Tiny;
try {
my $fetch = $client->fetch('foo', 'baz')->recv;
}
catch {
my $err = decode_json $_;
say "error: code => " . $err->[0] . " reason => " . $err->[1];
};
#+END_SRC
The error contains an array, with the first value the HTTP code, and the
second value the reason of the error given by Riak.
At the moment, the KiokuDB backend is not complete, but if you want to
start to play with is, all you need to do is:
#+BEGIN_SRC perl
my $dir = KiokuDB->new(
backend => KiokuDB::Backend::Riak->new(
db => AnyEvent::Riak->new(
host => 'http://localhost:8098',
path => 'jiak',
),
bucket => 'kiokudb',
),
);
$dir->txn_do(sub { $dir->insert($key => $object) });
#+END_SRC
|
