Merge branch 'project-authorizations-diff' into 'master'

Smarter refreshing of authorized projects

This MR reworks the way `User#refresh_authorized_projects`, resulting in a much more efficient process leading to fewer dead tuples.

Related issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/25257

See merge request !7956

1 files changed, 128 insertions, 0 deletions

diff --git a/app/services/users/refresh_authorized_projects_service.rb b/app/services/users/refresh_authorized_projects_service.rb
new file mode 100644
index 00000000000..7d38ac3a374
--- /dev/null
+++ b/app/services/users/refresh_authorized_projects_service.rb
@@ -0,0 +1,128 @@
+module Users
+  # Service for refreshing the authorized projects of a user.
+  #
+  # This particular service class can not be used to update data for the same
+  # user concurrently. Doing so could lead to an incorrect state. To ensure this
+  # doesn't happen a caller must synchronize access (e.g. using
+  # `Gitlab::ExclusiveLease`).
+  #
+  # Usage:
+  #
+  #     user = User.find_by(username: 'alice')
+  #     service = Users::RefreshAuthorizedProjectsService.new(some_user)
+  #     service.execute
+  class RefreshAuthorizedProjectsService
+    attr_reader :user
+
+    LEASE_TIMEOUT = 1.minute.to_i
+
+    # user - The User for which to refresh the authorized projects.
+    def initialize(user)
+      @user = user
+
+      # We need an up to date User object that has access to all relations that
+      # may have been created earlier. The only way to ensure this is to reload
+      # the User object.
+      user.reload
+    end
+
+    # This method returns the updated User object.
+    def execute
+      current = current_authorizations_per_project
+      fresh = fresh_access_levels_per_project
+
+      remove = current.each_with_object([]) do |(project_id, row), array|
+        # rows not in the new list or with a different access level should be
+        # removed.
+        if !fresh[project_id] || fresh[project_id] != row.access_level
+          array << row.id
+        end
+      end
+
+      add = fresh.each_with_object([]) do |(project_id, level), array|
+        # rows not in the old list or with a different access level should be
+        # added.
+        if !current[project_id] || current[project_id].access_level != level
+          array << [user.id, project_id, level]
+        end
+      end
+
+      update_with_lease(remove, add)
+    end
+
+    # Updates the list of authorizations using an exclusive lease.
+    def update_with_lease(remove = [], add = [])
+      lease_key = "refresh_authorized_projects:#{user.id}"
+      lease = Gitlab::ExclusiveLease.new(lease_key, timeout: LEASE_TIMEOUT)
+
+      until uuid = lease.try_obtain
+        # Keep trying until we obtain the lease. If we don't do so we may end up
+        # not updating the list of authorized projects properly. To prevent
+        # hammering Redis too much we'll wait for a bit between retries.
+        sleep(1)
+      end
+
+      begin
+        update_authorizations(remove, add)
+      ensure
+        Gitlab::ExclusiveLease.cancel(lease_key, uuid)
+      end
+    end
+
+    # Updates the list of authorizations for the current user.
+    #
+    # remove - The IDs of the authorization rows to remove.
+    # add - Rows to insert in the form `[user id, project id, access level]`
+    def update_authorizations(remove = [], add = [])
+      return if remove.empty? && add.empty?
+
+      User.transaction do
+        user.remove_project_authorizations(remove) unless remove.empty?
+        ProjectAuthorization.insert_authorizations(add) unless add.empty?
+        user.set_authorized_projects_column
+      end
+
+      # Since we batch insert authorization rows, Rails' associations may get
+      # out of sync. As such we force a reload of the User object.
+      user.reload
+    end
+
+    def fresh_access_levels_per_project
+      fresh_authorizations.each_with_object({}) do |row, hash|
+        hash[row.project_id] = row.access_level
+      end
+    end
+
+    def current_authorizations_per_project
+      current_authorizations.each_with_object({}) do |row, hash|
+        hash[row.project_id] = row
+      end
+    end
+
+    def current_authorizations
+      user.project_authorizations.select(:id, :project_id, :access_level)
+    end
+
+    def fresh_authorizations
+      ProjectAuthorization.
+        unscoped.
+        select('project_id, MAX(access_level) AS access_level').
+        from("(#{project_authorizations_union.to_sql}) #{ProjectAuthorization.table_name}").
+        group(:project_id)
+    end
+
+    private
+
+    # Returns a union query of projects that the user is authorized to access
+    def project_authorizations_union
+      relations = [
+        user.personal_projects.select("#{user.id} AS user_id, projects.id AS project_id, #{Gitlab::Access::MASTER} AS access_level"),
+        user.groups_projects.select_for_project_authorization,
+        user.projects.select_for_project_authorization,
+        user.groups.joins(:shared_projects).select_for_project_authorization
+      ]
+
+      Gitlab::SQL::Union.new(relations)
+    end
+  end
+end