* riak_id
** Overview
   =riak_id= is a very simple application that serves both to
   duplicate functionality from Twitter's [[https://github.com/twitter/snowflake]["Snowflake"]] and to teach,
   via a very simple example, how to build a [[https://github.com/basho/riak_core][riak_core]] application.
*** Design
    The core functionality of =riak_id= is to provide k-sorted unique
    identifiers.  The structure of the identifiers is very similar to
    Snowflake. They are 64-bit integers with the following layout
    (from highest to lowest):

    | Bits | Description                                   |
    |------+-----------------------------------------------|
    |    1 | Signedness flag, always 0                     |
    |   41 | Unix timestamp, down to the millisecond       |
    |   10 | Top 10 bits of partition number (see Caveats) |
    |   12 | Per-partition strictly increasing counter     |
    |------+-----------------------------------------------|
    
*** Caveats
    - Decent NTP synchronization between machines is needed for
      =riak_id= to work as expected.
    - Request failures (e.g. from partition, timeout) should simply be
      retried. You will eventually get an ID.
    - Because only 10 bits are reserved for the partition number,
      there is a practical ring-size limit of 1024.  This should not
      be a problem because the work is mostly CPU-bound.
    - So that we can give reasonable guarantees of uniqueness, some
      requests may have a minimum latency of 1ms (to allow the
      timestamp to increment).
    - It will run out of ID space within the century. Snowflake solves
      this using the "Twepoch". I didn't bother with that, but it
      would be a simple feature to add.
    - I wrote =riak_id= to learn, I hope it will be useful to others.

** Quick Start

   =riak_id= requires Erlang/OTP, [[https://github.com/basho/rebar][rebar]] and a sane GNU build system.

   1) Clone the repository, copy the =rebar= script into the repository.
   2) Run =make rel= from the command line.
   3) =rel/riak_id/bin/riak_id console=
   4) =riak_id:next_id().= from the console to generate IDs.

** Acknowledgments
   Thanks to Jesse Newland, Andy Gross, Ryan Zezeski for their work on
   the rebar template for riak_core apps, without which I would be
   lost. Special thanks to Andy for pointing out some egregious errors
   in an early version of the vnode code.

** License
   Copyright 2011, Sean Cribbs. Licensed under Apache License 2.0.