See https://dev.gitlab.org/gitlab/gitlabhq/issues/2643

Closes #2877

Performance of Gitlab::Git::Repository was improved in merge request
gitlab-org/gitlab_git!62.

Closes #4231

Also sorts them alphabetically, because OCD.

Closes #5908

Bundler keeps re-ordering this particular Gem every time something is
executed using "bundle exec".

Using the fuzzy filter, develop "file finder" feature.
- feedback(http://feedback.gitlab.com/forums/176466-general/suggestions/4987909-add-file-finder-fuzzy-input-in-files-tab-to-ju )
- fuzzy filter(https://github.com/jeancroy/fuzzaldrin-plus)
- shortcuts(when "t" was hitted at tree view, go to 'file find' page and 'esc' is to go back)
- depends on gitlab_git 7.2.22

Addresses #2857

Name: nokogiri
Version: 1.6.7
Advisory: CVE-2015-5312
Criticality: High
URL:
https://groups.google.com/forum/#!topic/ruby-security-ann/aSbgDiwb24s
Title: Nokogiri gem contains several vulnerabilities in libxml2
Solution: upgrade to >= 1.6.7.1

https://github.com/kickstarter/rack-attack/releases/tag/v4.3.1

This allows us to track the counts of actual classes instead of "T_XXX"
nodes. This is only enabled on CRuby as it uses CRuby specific APIs.

This works by searching the raw source code for any references to
commonly used ActiveRecord methods. While not bulletproof it saves us
from having to list hundreds of methods by hand. It also ensures that
(most) newly added methods are instrumented automatically.

This _only_ instruments models defined in app/models, should a model
reside somewhere else (e.g. somewhere in lib/) it _won't_ be
instrumented.

This adds the ability to write application metrics (e.g. SQL timings) to
InfluxDB. These metrics can in turn be visualized using Grafana, or
really anything else that can read from InfluxDB. These metrics can be
used to track application performance over time, between different Ruby
versions, different GitLab versions, etc.

== Transaction Metrics

Currently the following is tracked on a per transaction basis (a
transaction is a Rails request or a single Sidekiq job):

* Timings per query along with the raw (obfuscated) SQL and information
  about what file the query originated from.
* Timings per view along with the path of the view and information about
  what file triggered the rendering process.
* The duration of a request itself along with the controller/worker
  class and method name.
* The duration of any instrumented method calls (more below).

== Sampled Metrics

Certain metrics can't be directly associated with a transaction. For
example, a process' total memory usage is unrelated to any running
transactions. While a transaction can result in the memory usage going
up there's no accurate way to determine what transaction is to blame,
this becomes especially problematic in multi-threaded environments.

To solve this problem there's a separate thread that takes samples at a
fixed interval. This thread (using the class Gitlab::Metrics::Sampler)
currently tracks the following:

* The process' total memory usage.
* The number of file descriptors opened by the process.
* The amount of Ruby objects (using ObjectSpace.count_objects).
* GC statistics such as timings, heap slots, etc.

The default/current interval is 15 seconds, any smaller interval might
put too much pressure on InfluxDB (especially when running dozens of
processes).

== Method Instrumentation

While currently not yet used methods can be instrumented to track how
long they take to run. Unlike the likes of New Relic this doesn't
require modifying the source code (e.g. including modules), it all
happens from the outside. For example, to track `User.by_login` we'd add
the following code somewhere in an initializer:

    Gitlab::Metrics::Instrumentation.
      instrument_method(User, :by_login)

to instead instrument an instance method:

    Gitlab::Metrics::Instrumentation.
      instrument_instance_method(User, :save)

Instrumentation for either all public model methods or a few crucial
ones will be added in the near future, I simply haven't gotten to doing
so just yet.

== Configuration

By default metrics are disabled. This means users don't have to bother
setting anything up if they don't want to. Metrics can be enabled by
editing one's gitlab.yml configuration file (see
config/gitlab.yml.example for example settings).

== Writing Data To InfluxDB

Because InfluxDB is still a fairly young product I expect the worse.
Data loss, unexpected reboots, the database not responding, you name it.
Because of this data is _not_ written to InfluxDB directly, instead it's
queued and processed by Sidekiq. This ensures that users won't notice
anything when InfluxDB is giving trouble.

The metrics worker can be started in a standalone manner as following:

    bundle exec sidekiq -q metrics

The corresponding class is called MetricsWorker.

This reverts commit e426c027, reversing
changes made to c3676aa1.