Parallel ContactFrequency with Dask

In principle, each frame that makes up a ContactFrequency can have its contact map calculated in parallel. This shows how to use dask.distributed to do this.

This will use the same example data as the main contact maps example (data from See that example, contact_map.ipynb, for details.

%matplotlib inline
# dask and distributed are extra installs
from dask.distributed import Client, LocalCluster
import contact_map

First we need to connect a client to a dask network.

Note that there are several ways to set up the dask computer network and then connect a client to it. See The approach used here creates a LocalCluster. Large scale simulations would need other approaches. For clusters, you can manually run a dask-scheduler and multiple dask-worker commands. By using the same sched.json, it is easy to have different workers in different jobs on the cluster’s scheduling system.

c = LocalCluster()
client = Client(c)
# if you started on a cluster and the scheduler file is called sched.json
#client = Client(scheduler_file="./sched.json")



  • Workers: 4
  • Cores: 4
  • Memory: 17.18 GB
freq = contact_map.DaskContactFrequency(
# top must be given as keyword (passed along to mdtraj.load)
CPU times: user 954 ms, sys: 341 ms, total: 1.3 s
Wall time: 5.16 s

Note that on a single machine (shared memory) this may not improve performance. That is because the single-frame aspect of this calculation is already parallelized with OpenMP, and will therefore use all cores on the machine.

Next we check that we’re still getting the same results:

# did it add up to give us the right number of frames?
# do we get a familiar-looking residue map?
fig, ax = freq.residue_contacts.plot()
# Something like this is supposed to shut down the workers and the scheduler
# I get it to shut down workers, but not scheduler... and does it all with lots of warnings
#client.loop.add_callback(client.scheduler.retire_workers, close_workers=True)
#client.run_on_scheduler(lambda dask_scheduler: dask_scheduler.loop.stop())
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