riak_zab_example

Quick Start

Assuming you already have Erlang installed, clone this repository, and build it: make. Assuming all goes well, build a development release: make devrel.

Now, you can play around with things. For simplicity, I'm going to assume you're running within a X session and have xterm. Other scenarios are left as an exercise to the reader.

Start four Erlang nodes running riak_zab_example:

 > xterm -hold -e './dev/dev1/bin/riak_zab_example console' &
 > xterm -hold -e './dev/dev2/bin/riak_zab_example console' &
 > xterm -hold -e './dev/dev3/bin/riak_zab_example console' &
 > xterm -hold -e './dev/dev4/bin/riak_zab_example console' &

Join the four nodes into a single cluster. Joining all four nodes together sometimes results in riak_core making an unbalanced ring. This doesn't seem to occur if we first build a three node cluster, then add the fourth node. Note: You'll want to ensure that ringready returns TRUE (as shown) before moving to the next step.

 > ./dev/dev1/bin/riak-zab-admin join [email protected]
 Sent join request to [email protected]
 > ./dev/dev2/bin/riak-zab-admin join [email protected]
 Sent join request to [email protected]
 > ./dev/dev3/bin/riak-zab-admin join [email protected]
 Sent join request to [email protected]
 > ./dev/dev1/bin/riak-zab-admin ringready
 TRUE All nodes agree on the ring ['[email protected]','[email protected]',
                                   '[email protected]']

 > ./dev/dev4/bin/riak-zab-admin join [email protected]
 Sent join request to [email protected]
 > ./dev/dev4/bin/riak-zab-admin ringready
 TRUE All nodes agree on the ring ['[email protected]','[email protected]',
                                   '[email protected]','[email protected]']

Fire up Zab on all the nodes.

 > ./dev/dev1/bin/riak-zab-admin zab-up
 > ./dev/dev2/bin/riak-zab-admin zab-up
 > ./dev/dev3/bin/riak-zab-admin zab-up
 > ./dev/dev4/bin/riak-zab-admin zab-up

Assuming all goes well, you should see a few info messages on the node consoles that end with different ensembles successfully electing a leader. If the ring ended up being balanced, you should have a riak_zab state similar to the following.

 > ./dev/dev1/bin/riak-zab-admin info
 ================================ Riak Zab Info ================================
 Ring size:     64
 Ensemble size: 3
 Nodes:         ['[email protected]','[email protected]','[email protected]',
                 '[email protected]']
 ================================== Ensembles ==================================
 Ensemble     Ring   Leader                         Nodes
 -------------------------------------------------------------------------------
        1    25.0%   [email protected]                 ['[email protected]',
                                                     '[email protected]',
                                                     '[email protected]']
 -------------------------------------------------------------------------------
        2    25.0%   [email protected]                 ['[email protected]',
                                                     '[email protected]',
                                                     '[email protected]']
 -------------------------------------------------------------------------------
        3    25.0%   [email protected]                 ['[email protected]',
                                                     '[email protected]',
                                                     '[email protected]']
 -------------------------------------------------------------------------------
        4    25.0%   [email protected]                 ['[email protected]',
                                                     '[email protected]',
                                                     '[email protected]']
 -------------------------------------------------------------------------------

Up to this point you're dealing with standard riak_core / riak_zab. Now, let's play around a bit with the command set provided by riak_zab_example. The example app implements a simple list based log. There is a store command that appends elements to a list, and a get command that retrieves the current list. In your Erlang consoles, you can use commands in the following form:

 riak_zab_util:command(100, {store, 100, 1}, riak_zabexample_vnode_master).
 riak_zab_util:command(100, {store, 100, 6}, riak_zabexample_vnode_master).
 riak_zab_util:command(200, {store, 200, 1}, riak_zabexample_vnode_master).
 riak_zab_util:command(200, {store, 200, 6}, riak_zabexample_vnode_master).
 riak_zab_util:sync_command(100, {get, 100}, riak_zabexample_vnode_master).
 riak_zab_util:sync_command(200, {get, 200}, riak_zabexample_vnode_master).

Feel free to kill/restart nodes as desired, as well as send commands while a node is down and see what happens when the node restarts. For more verbose output, you can modify the riak_zab source in deps/riak_zab/src and enable all the DOUT defines to print output to the console and recompile. This should probably be made easier in the future.