Added Sherlock, a custom profiling tool for GitLab

Sherlock will be a new GitLab specific tool for measuring the
performance of Rails requests (and SideKiq jobs at some point). Some of
the things that are currently tracked:

* SQL queries along with their timings, backtraces and query plans
  (using "EXPLAIN ANALYZE" for PostgreSQL and regular "EXPLAIN" for
  MySQL)
* Timings of application files (including views) on a per line basis
* Some meta data such as the request method, path, total duration, etc

More tracking (e.g. Rugged or gitlab-shell timings) might be added in
the future.

Sherlock will replace any existing tools we have used so far (e.g.
active_record_query_trace and rack-mini-profiler), hence the
corresponding Gems have been removed from the Gemfile.

Sherlock can be enabled by starting Rails as following:

    ENABLE_SHERLOCK=1 bundle exec rails s

Recorded transactions can be found at `/sherlock/transactions`.

1 files changed, 50 insertions, 0 deletions

diff --git a/app/views/sherlock/queries/_general.html.haml b/app/views/sherlock/queries/_general.html.haml
new file mode 100644
index 00000000000..549b47430e6
--- /dev/null
+++ b/app/views/sherlock/queries/_general.html.haml
@@ -0,0 +1,50 @@
+.prepend-top-default
+  .panel.panel-default
+    .panel-heading
+      %strong
+        = t('sherlock.general')
+    %ul.well-list
+      %li
+        %span.light
+          #{t('sherlock.time')}:
+        %strong
+          = @query.duration.round(4)
+          = t('sherlock.milliseconds')
+      %li
+        %span.light
+          #{t('sherlock.origin')}:
+        %strong
+          = @query.last_application_frame.path
+        %small.light
+          = t('sherlock.line')
+          = @query.last_application_frame.line
+
+  .panel.panel-default
+    .panel-heading
+      .pull-right
+        %button.js-clipboard-trigger.btn.btn-xs{title: t('sherlock.copy_to_clipboard'), type: :button}
+          %i.fa.fa-clipboard
+        %pre.hidden
+          = @query.formatted_query
+      %strong
+        = t('sherlock.query')
+    %ul.well-list
+      %li
+        .code.js-syntax-highlight.sherlock-code
+          :preserve
+            #{highlight("#{@query.id}.sql", @query.formatted_query)}
+
+  .panel.panel-default
+    .panel-heading
+      .pull-right
+        %button.js-clipboard-trigger.btn.btn-xs{title: t('sherlock.copy_to_clipboard'), type: :button}
+          %i.fa.fa-clipboard
+        %pre.hidden
+          = @query.explain
+      %strong
+        = t('sherlock.query_plan')
+    %ul.well-list
+      %li
+        .code.js-syntax-highlight.sherlock-code
+          %pre
+            %code= @query.explain