From https://github.com/wsexport/tool/issues/127
It would be nicer to write temporary files to the actual /tmp directory rather than to a directory in the tool's $HOME. You may need to write to $HOME eventually for delivery of results via the http service, but doing all the work to the NFS filesystem is causing high I/O load spikes. See https://phabricator.wikimedia.org/T161898#3180464 for some examination.
Ideally the web interface would use some queuing mechanism to limit the number of parallel conversion jobs that are used to avoid work spikes that overload I/O and processing power on the shared job grid. This could be accomplished using the Redis server as a queue and a small number of dedicated jobs that polled Redis for work to do. I'd actually suggest starting with just a single worker and monitoring the queue depth for a week or two to determine if wait times actually warrant using more than a single worker.