Eliminate cached N+1 queries for projects in Issue API
In CE, every
Issue entity is also a
ProjectEntity, which calls
entity&.project.try(:id) to show the project ID. In an API
request with 100 issues, this would hit the Rails statement cache 100 times
for the same project and cause unnecessary overhead as related models would
also be loaded.
In EE, we call
Issue#supports_weight? for each issue, which then calls
project&.feature_available?(:issue_weights). If the project is not
preloaded, this incurs additional overhead, as each individual Project
object has to be queried. This can lead to a significant performance hit.
In loading the CE project with 100 issues, this contributed to at least 22%
of the load time.
See https://gitlab.com/gitlab-org/gitlab-ce/issues/47031 for why testing this is a bit tricky.