Greatly improve external_issue_tracker performanceimprove-project-external-issue-trackers

This greatly improves the performance of Project#external_issue_tracker
by moving most of the fields queried in Ruby to the database and letting
the database handle all logic. Prior to this change the process of
finding an external issue tracker was along the lines of the following:

1. Load all project services into memory.
2. Reduce the list to only services where "issue_tracker?" returns true
3. Reduce the list from step 2 to service where "default?" returns false
4. Find the first service where "activated?" returns true

This has to two big problems:

1. Loading all services into memory only to reduce the list down to a
   single item later on is a waste of memory (and slow timing wise).
2. Calling Array#select followed by Array#reject followed by Array#find
   allocates extra objects when this really isn't needed.

To work around this the following service fields have been moved to the
database (instead of being hardcoded):

* category
* default

This in turn means we can get the external issue tracker using the
following query:

    SELECT *
    FROM services
    WHERE active IS TRUE
    AND default IS FALSE
    AND category = 'issue_tracker'
    AND project_id = XXX
    LIMIT 1

This coupled with memoizing the result (just as before this commit)
greatly reduces the time it takes for Project#external_issue_tracker to
complete. The exact reduction depends on one's environment, but locally
the execution time is reduced from roughly 230 ms to only 2 ms (= a
reduction of almost 180x).

Fixes gitlab-org/gitlab-ce#10771

1 files changed, 8 insertions, 3 deletions

diff --git a/app/models/service.rb b/app/models/service.rb
index 24f4bf7646e..721273250ea 100644
--- a/app/models/service.rb
+++ b/app/models/service.rb
@@ -43,6 +43,9 @@ class Service < ActiveRecord::Base
   validates :project_id, presence: true, unless: Proc.new { |service| service.template? }
 
   scope :visible, -> { where.not(type: ['GitlabIssueTrackerService', 'GitlabCiService']) }
+  scope :issue_trackers, -> { where(category: 'issue_tracker') }
+  scope :active, -> { where(active: true) }
+  scope :without_defaults, -> { where(default: false) }
 
   scope :push_hooks, -> { where(push_events: true, active: true) }
   scope :tag_push_hooks, -> { where(tag_push_events: true, active: true) }
@@ -51,6 +54,8 @@ class Service < ActiveRecord::Base
   scope :note_hooks, -> { where(note_events: true, active: true) }
   scope :build_hooks, -> { where(build_events: true, active: true) }
 
+  default_value_for :category, 'common'
+
   def activated?
     active
   end
@@ -60,7 +65,7 @@ class Service < ActiveRecord::Base
   end
 
   def category
-    :common
+    read_attribute(:category).to_sym
   end
 
   def initialize_properties
@@ -153,7 +158,7 @@ class Service < ActiveRecord::Base
 
   # Returns a hash of the properties that have been assigned a new value since last save,
   # indicating their original values (attr => original value).
-  # ActiveRecord does not provide a mechanism to track changes in serialized keys, 
+  # ActiveRecord does not provide a mechanism to track changes in serialized keys,
   # so we need a specific implementation for service properties.
   # This allows to track changes to properties set with the accessor methods,
   # but not direct manipulation of properties hash.
@@ -164,7 +169,7 @@ class Service < ActiveRecord::Base
   def reset_updated_properties
     @updated_properties = nil
   end
-  
+
   def async_execute(data)
     return unless supported_events.include?(data[:object_kind])