Reduce Gitaly calls in PostReceive
This commit reduces I/O load and memory utilization during PostReceive
for the common case when no project hooks or services are set up.
We saw a Gitaly N+1 issue in CommitDelta when many tags or branches
are pushed. We can reduce this overhead in the common case because we observe that
most new projects do not have any Web hooks or services, especially when
they are first created. Previously, BaseHooksService unconditionally
iterated through the last 20 commits of each ref to build the
push_data structure. The push_data structured was used in numerous
places:
- Building the push payload in
EventCreateService - Creating a CI pipeline
- Executing project Web or system hooks
- Executing project services
- As the return value of
BaseHooksService#execute - Finding files to invalidate the cache in
BranchHooksService#invalidated_file_types
We only need to generate the full push_data for items 3, 4, and 6.
Item 1: EventCreateService only needs the last commit and doesn't
actually need the commit deltas.
Item 2: In addition, Ci::CreatePipelineService only needed a subset of
the parameters.
Item 5: The return value of BaseHooksService#execute also wasn't being
used anywhere.
Item 6: This is only used when pushing to the default branch, so if many tags are pushed we can save significant I/O here.