Adding a batch of works to a collection (performance issue)

[dolsysmith]

Adding works to a collection via the dashboard dispatches a series of ContentUpdateEventJobs to Sidekiq. Each job triggers a number of calls to Fedora. It may be hitting the limits of Fedora, but adding ~60 works to a new collection in a batch took about 45 minutes on the test server and a few hours on prod.

Are there performance bottlenecks anywhere that we can mitigate? Is this a known performance issue?

See also #550