Merge branch '33929-allow-to-enable-perf-bar-for-a-group' into 'master'

Allow to enable the performance bar per user or Feature group

Closes #33929 and #34528

See merge request !12362

9 files changed, 56 insertions, 4 deletions

diff --git a/doc/README.md b/doc/README.md
index ebf1a0415d2..9b81c409570 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -167,6 +167,7 @@ have access to GitLab administration tools and settings.
 - [Operations](administration/operations.md): Keeping GitLab up and running.
 - [Polling](administration/polling.md): Configure how often the GitLab UI polls for updates.
 - [Request Profiling](administration/monitoring/performance/request_profiling.md): Get a detailed profile on slow requests.
+- [Performance Bar](administration/monitoring/performance/performance_bar.md): Get performance information for the current page.
 
 ### Customization
 
diff --git a/doc/administration/monitoring/performance/img/performance_bar.png b/doc/administration/monitoring/performance/img/performance_bar.png
new file mode 100644
index 00000000000..d38293d2ed6
--- /dev/null
+++ b/doc/administration/monitoring/performance/img/performance_bar.png
diff --git a/doc/administration/monitoring/performance/img/performance_bar_configuration_settings.png b/doc/administration/monitoring/performance/img/performance_bar_configuration_settings.png
new file mode 100644
index 00000000000..2d64ef8c5fc
--- /dev/null
+++ b/doc/administration/monitoring/performance/img/performance_bar_configuration_settings.png
diff --git a/doc/administration/monitoring/performance/img/performance_bar_line_profiling.png b/doc/administration/monitoring/performance/img/performance_bar_line_profiling.png
new file mode 100644
index 00000000000..7868e2c46d1
--- /dev/null
+++ b/doc/administration/monitoring/performance/img/performance_bar_line_profiling.png
diff --git a/doc/administration/monitoring/performance/img/performance_bar_sql_queries.png b/doc/administration/monitoring/performance/img/performance_bar_sql_queries.png
new file mode 100644
index 00000000000..372ae021f6b
--- /dev/null
+++ b/doc/administration/monitoring/performance/img/performance_bar_sql_queries.png
diff --git a/doc/administration/monitoring/performance/performance_bar.md b/doc/administration/monitoring/performance/performance_bar.md
new file mode 100644
index 00000000000..ee680c7b258
--- /dev/null
+++ b/doc/administration/monitoring/performance/performance_bar.md
@@ -0,0 +1,35 @@
+# Performance Bar
+
+A Performance Bar can be displayed, to dig into the performance of a page. When
+activated, it looks as follows:
+
+![Performance Bar](img/performance_bar.png)
+
+It allows you to:
+
+- see the current host serving the page
+- see the timing of the page (backend, frontend)
+- the number of DB queries, the time it took, and the detail of these queries
+![SQL profiling using the Performance Bar](img/performance_bar_sql_queries.png)
+- the number of calls to Redis, and the time it took
+- the number of background jobs created by Sidekiq, and the time it took
+- the number of Ruby GC calls, and the time it took
+- profile the code used to generate the page, line by line
+![Line profiling using the Performance Bar](img/performance_bar_line_profiling.png)
+
+## Enable the Performance Bar via the Admin panel
+
+GitLab Performance Bar is disabled by default. To enable it for a given group,
+navigate to the Admin area in **Settings > Profiling - Performance Bar**
+(`/admin/application_settings`).
+
+The only required setting you need to set is the full path of the group that
+will be allowed to display the Performance Bar.
+Make sure _Enable the Performance Bar_ is checked and hit
+**Save** to save the changes.
+
+---
+
+![GitLab Performance Bar Admin Settings](img/performance_bar_configuration_settings.png)
+
+---
diff --git a/doc/api/README.md b/doc/api/README.md
index b7f6ee69193..95e7a457848 100644
--- a/doc/api/README.md
+++ b/doc/api/README.md
@@ -17,6 +17,7 @@ following locations:
 - [Deploy Keys](deploy_keys.md)
 - [Environments](environments.md)
 - [Events](events.md)
+- [Feature flags](features.md)
 - [Gitignores templates](templates/gitignores.md)
 - [GitLab CI Config templates](templates/gitlab_ci_ymls.md)
 - [Groups](groups.md)
diff --git a/doc/api/features.md b/doc/api/features.md
index 558869255cc..6861dbf00a2 100644
--- a/doc/api/features.md
+++ b/doc/api/features.md
@@ -1,4 +1,4 @@
-# Features API
+# Features flags API
 
 All methods require administrator authorization.
 
@@ -61,7 +61,8 @@ POST /features/:name
 | `feature_group` | string | no | A Feature group name |
 | `user` | string | no | A GitLab username |
 
-Note that `feature_group` and `user` are mutually exclusive.
+Note that you can enable or disable a feature for both a `feature_group` and a
+`user` with a single API call.
 
 ```bash
 curl --data "value=30" --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/features/new_library
diff --git a/doc/development/feature_flags.md b/doc/development/feature_flags.md
index 5c6316b9ac6..59e8a087e02 100644
--- a/doc/development/feature_flags.md
+++ b/doc/development/feature_flags.md
@@ -3,5 +3,19 @@
 Starting from GitLab 9.3 we support feature flags via
 [Flipper](https://github.com/jnunemaker/flipper/). You should use the `Feature`
 class (defined in `lib/feature.rb`) in your code to get, set and list feature
-flags. During runtime you can set the values for the gates via the
-[admin API](../api/features.md).
+flags.
+
+During runtime you can set the values for the gates via the
+[features API](../api/features.md) (accessible to admins only).
+
+## Feature groups
+
+Starting from GitLab 9.4 we support feature groups via
+[Flipper groups](https://github.com/jnunemaker/flipper/blob/v0.10.2/docs/Gates.md#2-group).
+
+Feature groups must be defined statically in `lib/feature.rb` (in the
+`.register_feature_groups` method), but their implementation can obviously be
+dynamic (querying the DB etc.).
+
+Once defined in `lib/feature.rb`, you will be able to activate a
+feature for a given feature group via the [`feature_group` param of the features API](../api/features.md#set-or-create-a-feature)