Improve performance of the cycle analytics page.

1. These changes bring down page load time for 100 issues from more than
   a minute to about 1.5 seconds.

2. This entire commit is composed of these types of performance
   enhancements:

     - Cache relevant data in `IssueMetrics` wherever possible.
     - Cache relevant data in `MergeRequestMetrics` wherever possible.
     - Preload metrics

3. Given these improvements, we now only need to make 4 SQL calls:

    - Load all issues
    - Load all merge requests
    - Load all metrics for the issues
    - Load all metrics for the merge requests

4. A list of all the data points that are now being pre-calculated:

    a. The first time an issue is mentioned in a commit

      - In `GitPushService`, find all issues mentioned by the given commit
        using `ReferenceExtractor`. Set the `first_mentioned_in_commit_at`
        flag for each of them.

      - There seems to be a (pre-existing) bug here - files (and
        therefore commits) created using the Web CI don't have
        cross-references created, and issues are not closed even when
        the commit title is "Fixes #xx".

    b. The first time a merge request is deployed to production

      When a `Deployment` is created, find all merge requests that
      were merged in before the deployment, and set the
      `first_deployed_to_production_at` flag for each of them.

    c. The start / end time for a merge request pipeline

      Hook into the `Pipeline` state machine. When the `status` moves to
      `running`, find the merge requests whose tip commit matches the
      pipeline, and record the `latest_build_started_at` time for each
      of them. When the `status` moves to `success`, record the
      `latest_build_finished_at` time.

    d. The merge requests that close an issue

      - This was a big cause of the performance problems we were having
        with Cycle Analytics. We need to use `ReferenceExtractor` to make
        this calculation, which is slow when we have to run it on a large
        number of merge requests.

      - When a merge request is created, updated, or refreshed, find the
        issues it closes, and create an instance of
        `MergeRequestsClosingIssues`, which acts as a join model between
        merge requests and issues.

      - If a `MergeRequestsClosingIssues` instance links a merge request
        and an issue, that issue closes that merge request.

5. The `Queries` module was changed into a class, so we can cache the
   results of `issues` and `merge_requests_closing_issues` across
   various cycle analytics stages.

6. The code added in this commit is untested. Tests will be added in the
   next commit.

6 files changed, 155 insertions, 5 deletions

diff --git a/db/fixtures/development/17_cycle_analytics.rb b/db/fixtures/development/17_cycle_analytics.rb
index 6d5a28c2e81..46cf0fbd805 100644
--- a/db/fixtures/development/17_cycle_analytics.rb
+++ b/db/fixtures/development/17_cycle_analytics.rb
@@ -24,30 +24,37 @@ class Gitlab::Seeder::CycleAnalytics
   def seed!
     Sidekiq::Testing.inline! do
       issues = create_issues(@project)
+      print '.'
 
       # Stage 1
       Timecop.travel 5.days.from_now
       add_milestones_and_list_labels(issues)
+      print '.'
 
       # Stage 2
       Timecop.travel 5.days.from_now
       branches = mention_in_commits(issues)
+      print '.'
 
       # Stage 3
       Timecop.travel 5.days.from_now
       merge_requests = create_merge_requests_closing_issues(issues, branches)
+      print '.'
 
       # Stage 4
       Timecop.travel 5.days.from_now
       run_builds(merge_requests)
+      print '.'
 
       # Stage 5
       Timecop.travel 5.days.from_now
       merge_merge_requests(merge_requests)
+      print '.'
 
       # Stage 6 / 7
       Timecop.travel 5.days.from_now
       deploy_to_production(merge_requests)
+      print '.'
     end
 
     print '.'
@@ -101,8 +108,14 @@ class Gitlab::Seeder::CycleAnalytics
       }
 
       commit_sha = Gitlab::Git::Blob.commit(issue.project.repository, options)
-      commit = issue.project.repository.commit(commit_sha)
-      commit.create_cross_references!
+      issue.project.repository.commit(commit_sha)
+
+
+      GitPushService.new(issue.project,
+                         @user,
+                         oldrev: issue.project.repository.commit("master").sha,
+                         newrev: commit_sha,
+                         ref: 'refs/heads/master').execute
 
       branch_name
     end
@@ -162,10 +175,12 @@ end
 
 Gitlab::Seeder.quiet do
   if ENV['SEED_CYCLE_ANALYTICS']
-      seeder = Gitlab::Seeder::CycleAnalytics.new(Project.find(1))
+    Project.all.each do |project|
+      seeder = Gitlab::Seeder::CycleAnalytics.new(project)
       seeder.seed!
+    end
   elsif ENV['CYCLE_ANALYTICS_PERF_TEST']
-    seeder = Gitlab::Seeder::CycleAnalytics.new(Project.first, perf: true)
+    seeder = Gitlab::Seeder::CycleAnalytics.new(Project.order(:id).first, perf: true)
     seeder.seed!
   else
     puts "Not running the cycle analytics seed file. Use the `SEED_CYCLE_ANALYTICS` environment variable to enable it."
diff --git a/db/migrate/20160915042921_create_merge_requests_closing_issues.rb b/db/migrate/20160915042921_create_merge_requests_closing_issues.rb
new file mode 100644
index 00000000000..bc0814eeaeb
--- /dev/null
+++ b/db/migrate/20160915042921_create_merge_requests_closing_issues.rb
@@ -0,0 +1,34 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class CreateMergeRequestsClosingIssues < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = true
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  DOWNTIME_REASON = 'Adding foreign keys'
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def change
+    create_table :merge_requests_closing_issues do |t|
+      t.references :merge_request, foreign_key: true, null: false
+      t.references :issue, foreign_key: true, null: false
+
+      t.timestamps null: false
+    end
+  end
+end
diff --git a/db/migrate/20160915061248_add_production_deploy_time_to_merge_request_metrics.rb b/db/migrate/20160915061248_add_production_deploy_time_to_merge_request_metrics.rb
new file mode 100644
index 00000000000..34dacfc994b
--- /dev/null
+++ b/db/migrate/20160915061248_add_production_deploy_time_to_merge_request_metrics.rb
@@ -0,0 +1,29 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddProductionDeployTimeToMergeRequestMetrics < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def change
+    add_column :merge_request_metrics, :first_deployed_to_production_at, :datetime
+  end
+end
diff --git a/db/migrate/20160915072217_add_first_mentioned_in_commit_time_to_issue_metrics.rb b/db/migrate/20160915072217_add_first_mentioned_in_commit_time_to_issue_metrics.rb
new file mode 100644
index 00000000000..6c1a388ff3f
--- /dev/null
+++ b/db/migrate/20160915072217_add_first_mentioned_in_commit_time_to_issue_metrics.rb
@@ -0,0 +1,29 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddFirstMentionedInCommitTimeToIssueMetrics < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def change
+    add_column :issue_metrics, :first_mentioned_in_commit_at, :datetime
+  end
+end
diff --git a/db/migrate/20160915081353_add_latest_build_time_to_merge_request_metrics.rb b/db/migrate/20160915081353_add_latest_build_time_to_merge_request_metrics.rb
new file mode 100644
index 00000000000..b413e6103c9
--- /dev/null
+++ b/db/migrate/20160915081353_add_latest_build_time_to_merge_request_metrics.rb
@@ -0,0 +1,30 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddLatestBuildTimeToMergeRequestMetrics < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  # Set this constant to true if this migration requires downtime.
+  DOWNTIME = false
+
+  # When a migration requires downtime you **must** uncomment the following
+  # constant and define a short and easy to understand explanation as to why the
+  # migration requires downtime.
+  # DOWNTIME_REASON = ''
+
+  # When using the methods "add_concurrent_index" or "add_column_with_default"
+  # you must disable the use of transactions as these methods can not run in an
+  # existing transaction. When using "add_concurrent_index" make sure that this
+  # method is the _only_ method called in the migration, any other changes
+  # should go in a separate migration. This ensures that upon failure _only_ the
+  # index creation fails and can be retried or reverted easily.
+  #
+  # To disable transactions uncomment the following line and remove these
+  # comments:
+  # disable_ddl_transaction!
+
+  def change
+    add_column :merge_request_metrics, :latest_build_started_at, :datetime
+    add_column :merge_request_metrics, :latest_build_finished_at, :datetime
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 2c380de3d50..26d49e7b261 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160901141443) do
+ActiveRecord::Schema.define(version: 20160915081353) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -442,6 +442,7 @@ ActiveRecord::Schema.define(version: 20160901141443) do
     t.datetime "first_added_to_board_at"
     t.datetime "created_at",                         null: false
     t.datetime "updated_at",                         null: false
+    t.datetime "first_mentioned_in_commit_at"
   end
 
   add_index "issue_metrics", ["issue_id"], name: "index_issue_metrics", using: :btree
@@ -596,6 +597,9 @@ ActiveRecord::Schema.define(version: 20160901141443) do
     t.datetime "first_closed_at"
     t.datetime "created_at",                               null: false
     t.datetime "updated_at",                               null: false
+    t.datetime "first_deployed_to_production_at"
+    t.datetime "latest_build_started_at"
+    t.datetime "latest_build_finished_at"
   end
 
   add_index "merge_request_metrics", ["merge_request_id"], name: "index_merge_request_metrics", using: :btree
@@ -641,6 +645,13 @@ ActiveRecord::Schema.define(version: 20160901141443) do
   add_index "merge_requests", ["title"], name: "index_merge_requests_on_title", using: :btree
   add_index "merge_requests", ["title"], name: "index_merge_requests_on_title_trigram", using: :gin, opclasses: {"title"=>"gin_trgm_ops"}
 
+  create_table "merge_requests_closing_issues", force: :cascade do |t|
+    t.integer  "merge_request_id", null: false
+    t.integer  "issue_id",         null: false
+    t.datetime "created_at",       null: false
+    t.datetime "updated_at",       null: false
+  end
+
   create_table "milestones", force: :cascade do |t|
     t.string   "title",       null: false
     t.integer  "project_id",  null: false
@@ -1170,6 +1181,8 @@ ActiveRecord::Schema.define(version: 20160901141443) do
   add_foreign_key "lists", "boards"
   add_foreign_key "lists", "labels"
   add_foreign_key "merge_request_metrics", "merge_requests"
+  add_foreign_key "merge_requests_closing_issues", "issues"
+  add_foreign_key "merge_requests_closing_issues", "merge_requests"
   add_foreign_key "personal_access_tokens", "users"
   add_foreign_key "protected_branch_merge_access_levels", "protected_branches"
   add_foreign_key "protected_branch_push_access_levels", "protected_branches"