MediaWiki:Gwtoolset-mediafile-throttle-description/en

After the batch preview, in step 3, GWToolset uploads the remaining records in your batch upload via background jobs. The mediafile throttle controls the number of mediafile requests Wikimedia Commons will make against your mediafile server each time a background job is run. You can set the mediafile throttle between 1-20. For example, if the total number of records in your batch upload is 100 and you set the throttle to 20, Wikimedia Commons will run 5 background jobs in order to process your entire batch upload. The time between each background upload job varies depending on server load and configuration. We anticipate that on Wikimedia Commons a GWToolset background job will run at least every 5 minutes.