Open Source Ecosystems

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.

Clone the repository, copy the =rebar= script into the repository.
Run =make rel= from the command line.
=rel/riak_id/bin/riak_id console=
=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.