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    Reduce Gitaly calls in PostReceive · dd57e6317344
    Stan Hu authored
    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:
    
    1. Building the push payload in `EventCreateService`
    2. Creating a CI pipeline
    3. Executing project Web or system hooks
    4. Executing project services
    5. As the return value of `BaseHooksService#execute`
    6. `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.
    
    Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/65878
    
    Fic
    dd57e6317344