In this post I describe how the easiest way to run Riak with a debug build of the Erlang VM. While I focus specifically on Riak, this procedure should hold true for most Erlang projects that are set up for release builds using rebar.

First, make sure the debug build of Erlang is the first in your path. If you have not built a debug-enabled Erlang VM, I covered how to accomplish that in a prior post and you can find it here.

Next navigate to your Riak repository and do a clean and release build of Riak.

make clean rel

Move to the Riak release directory and open the riak script in an editor.

cd rel/riak
emacs bin/riak

Look for the line EMU=beam. It should be located somewhere around line 228 in the section for the console command. Change that line to EMU=beam.debug and save the file.

Now you are ready to start up Riak. For this example I just start it with console instead of start.

./bin/riak console

You should notice the Erlang banner is slightly different than normal. Using the normal Erlang VM the banner looks something like this:

Erlang R15B (erts-5.9) [source] [64-bit] [smp:4:4] [async-threads:64] [kernel-poll:true]

However using the debug-enabled VM, it should look something like the following:

Erlang R15B (erts-5.9) [source] [64-bit] [smp:4:4] [async-threads:64] [kernel-poll:true] [type-assertions] [debug-compiled] [lock-checking]

And that’s all there is to it. Once you have the debug-enabled Erlang VM built, it’s very easy to get Riak up and running with it. It may go without saying, but Riak will run noticeably slower using the debug-enabled VM so please do not run in this manner in production. Happy debugging!