gen_q

An Erlang port driver for bridging an Erlang app and a q process, implemented with asyncronous tasks to allow parallel execution. Built on top of kx's C bindings (c.o).

Works for Mac OSX and Linux, developed on OS X Mavericks and CentOS 6.4, running on a production kdb+ instance that writes more than 7 GB of data daily.

gen_q implements q's full list of rich data types and provides access to arbitrary q function calls via IPC. With gen_q, you can feed your tickerplant directly from an Erlang application, and you can run queries to pull data back out again.

Getting started

Add the following to your Erlang app's rebar.config.

{gen_q, ".*", {git, "git@github.com:republicwireless-open/gen_q.git", {tag, "1.0"}}}

Before compiling, if your target q process is version 3 or higher, you must edit gen_q's rebar.config and add -DKXVER=3 to the CFLAGS. Then, compile and start your app.

Start the port driver with the following command.

> {ok, _Pid} = q:start_link().
{ok,<0.1401.0>}

Open an IPC handle to your q process.

%                   Host         Port  Credentials          Timeout
> {ok, H} = q:hopen("localhost", 5000, "username:password", 10000).
{ok,18}

Evaluate a q expression from Erlang.

> q:eval(H, "2+2").
{ok,{long,4}}

Notice that results returned from the q module include the data type from the q result. This gets more interesting with some of q's more esoteric types.

> q:eval(H, ".z.p").
{ok,{timestamp,478041037666903000}}

You can also call functions.

> q:apply(H, sum, {list, float}, [1,2,3]).
{ok,{float,6.0}}

And close your connection.

> q:hclose(H).
ok

See the unit tests in test/gen_q_port_tests.erl for more examples. Building and Dependencies

If you're targeting a q instance version 3 or higher, you must add -DKXVER=3 to your CFLAGS in gen_q's rebar.config.

If you're compiling for Darwin (Mac OS X), there are a couple caveats:

• A 32bit version of libgcc_s.1 is required. The rebar.config includes the path /opt/local/lib/gcc48 in an attempt to locate the file. Edit as needed.
• On Darwin, gen_q does not compile within the rebar dependency tree. Change directory to deps/gen_q and run make from there.

Development

Run the unit tests with

make test

Note that due to an unknown issue with port drivers running inside a rebar eunit task, rebar may SEGFAULT after all the tests have run successfully. This is being tracked in the open issues.