Multi-run

Sometimes you want to run a parameter sweep. A parameter sweep is a method of evaluating a function (or a program) with a pre-determined set of parameters. The examples below will clarify what this means.

To run a parameter sweep, use the --multirun (-m) flag and pass a comma separated list for each dimension you want to sweep.

To run your program with the 3 different schemas in schema config group:

$ python my_app.py -m schema=warehouse,support,school

Here is sweep over the db types (mysql,postgresql) and the schemas (warehouse,support,school). Output does not contain the configuration prints.

 $ python my_app.py schema=warehouse,support,school db=mysql,postgresql -m
[2019-10-01 14:44:16,254] - Launching 6 jobs locally
[2019-10-01 14:44:16,254] - Sweep output dir : multirun/2019-10-01/14-44-16
[2019-10-01 14:44:16,254] -     #0 : schema=warehouse db=mysql
[2019-10-01 14:44:16,321] -     #1 : schema=warehouse db=postgresql
[2019-10-01 14:44:16,390] -     #2 : schema=support db=mysql
[2019-10-01 14:44:16,458] -     #3 : schema=support db=postgresql
[2019-10-01 14:44:16,527] -     #4 : schema=school db=mysql
[2019-10-01 14:44:16,602] -     #5 : schema=school db=postgresql

info

Hydra supports other kind of sweeps, for example a range sweep: x=range(1,10) or a glob: support=glob(*).
See the Extended Override syntax for details.

Sweeper

The sweeping logic is implemented by a simple sweeper that is built into Hydra. Additional sweepers are available as plugins. For example, the Ax Sweeper can automatically find the best parameter combination!

Launcher

A Launcher is what runs your job. Hydra comes with a simple launcher that runs the jobs locally and serially. Other launchers are available as plugins for launching in parallel and on different clusters. For example, the JobLib Launcher can execute the different parameter combinations in parallel on your local machine using multi-processing.