• Stan Hu's avatar
    Remove N+1 SQL query loading project feature in dashboard · 29e60b06
    Stan Hu authored
    Projects that have a pipeline may need to check whether the user has
    permission to read the build (`can?(current_user, :read_build,
    project)`), which requires checking the `project_features` table.
    This would cause an N+1 SQL query for each project.
    
    This change also has a beneficial side effect that may avoid a race
    condition. When a user deletes a project, the project is queued for
    deletion and the user is redirected back to the dashboard page. However,
    the following may happen:
    
    1. The dashboard page may load this deleted project in the list of
    20 projects.
    2. The view will load the project pipeline status from the cache and
    attempt to show each project.
    3. When the view encounters the deleted project, it calls
    `can?(current_user, :read_build, project)` to determine whether to
    display the pipeline status.
    4. Sidekiq deletes the project from the database.
    5. However, since the deleted project is still loaded in memory, it will
    attempt to call `project.project_feature.access_level`.
    6. Since `project_feature` was not eager loaded, a lazy `SELECT` call is
    made to the database.
    7. This `SELECT` call returns nothing, and the user sees a 500 error.
    
    By eager loading `project_feature`, we can ensure that we have a
    consistent view and avoid records from being deleted later.
    
    Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/66482
    29e60b06
sh-project-feature-nplus-one.yml 116 Bytes