Version 3.1.0 features massive performance improvements for larger instances.
Pull requests are indexed via existing elastic-search by title, description, project, label, due-date, author, reviewers, target branches, state etc.
Search for Pull Requests like
project = MY_PROJ & target = develop, master & text = "my annoying client" & label IN urgent, release
Pull Request Indexing needs to be enabled in Bitbucket admin > Organizr configuration. Perform a re-index after enabling.
See the release notes for all the delicious details.