Mention limitations of MySQL in docs

3 files changed, 50 insertions, 58 deletions

diff --git a/doc/install/requirements.md b/doc/install/requirements.md
index 197a92905c8..e2b1c24d25b 100644
--- a/doc/install/requirements.md
+++ b/doc/install/requirements.md
@@ -86,56 +86,30 @@ if your available memory changes.
 
 Notice: The 25 workers of Sidekiq will show up as separate processes in your process overview (such as top or htop) but they share the same RAM allocation since Sidekiq is a multithreaded application. Please see the section below about Unicorn workers for information about many you need of those.
 
-## GitLab Runner
-
-We strongly advise against installing GitLab Runner on the same machine you plan
-to install GitLab on. Depending on how you decide to configure GitLab Runner and
-what tools you use to exercise your application in the CI environment, GitLab
-Runner can consume significant amount of available memory.
-
-Memory consumption calculations, that are available above, will not be valid if
-you decide to run GitLab Runner and the GitLab Rails application on the same
-machine.
-
-It is also not safe to install everything on a single machine, because of the
-[security reasons] - especially when you plan to use shell executor with GitLab
-Runner.
-
-We recommend using a separate machine for each GitLab Runner, if you plan to
-use the CI features.
-
-[security reasons]: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/blob/master/docs/security/index.md
-
-## Unicorn Workers
-
-It's possible to increase the amount of unicorn workers and this will usually help to reduce the response time of the applications and increase the ability to handle parallel requests.
-
-For most instances we recommend using: CPU cores + 1 = unicorn workers.
-So for a machine with 2 cores, 3 unicorn workers is ideal.
-
-For all machines that have 2GB and up we recommend a minimum of three unicorn workers.
-If you have a 1GB machine we recommend to configure only two Unicorn workers to prevent excessive swapping.
-
-To change the Unicorn workers when you have the Omnibus package please see [the Unicorn settings in the Omnibus GitLab documentation](https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/doc/settings/unicorn.md#unicorn-settings).
-
 ## Database
 
+The server running the database should have _at least_ 5-10 GB of storage
+available, though the exact requirements depend on the size of the GitLab
+installation (e.g. the number of users, projects, etc).
+
 We currently support the following databases:
 
 - PostgreSQL
 - MySQL/MariaDB
 
-We _highly_ recommend the use of PostgreSQL instead of MySQL/MariaDB as not all
-features of GitLab may work with MySQL/MariaDB. For example, MySQL does not have
-the right features to support nested groups in an efficient manner; see
-<https://gitlab.com/gitlab-org/gitlab-ce/issues/30472> for more information
-about this. GitLab Geo also does [not support MySQL](https://docs.gitlab.com/ee/gitlab-geo/database.html#mysql-replication).
+We **highly recommend** the use of PostgreSQL instead of MySQL/MariaDB as not all
+features of GitLab may work with MySQL/MariaDB:
+
+1. MySQL support for subgroups was dropped with GitLab 9.3.
+   See [issue #30472][30472] for more information.
+1. GitLab Geo does [not support MySQL](https://docs.gitlab.com/ee/gitlab-geo/database.html#mysql-replication).
+1. [Zero downtime migrations][zero] do not work with MySQL
+
 Existing users using GitLab with MySQL/MariaDB are advised to
-migrate to PostgreSQL instead.
+[migrate to PostgreSQL](../update/mysql_to_postgresql.md) instead.
 
-The server running the database should have _at least_ 5-10 GB of storage
-available, though the exact requirements depend on the size of the GitLab
-installation (e.g. the number of users, projects, etc).
+[30472]: https://gitlab.com/gitlab-org/gitlab-ce/issues/30472
+[zero]: ../update/README.md#upgrading-without-downtime
 
 ### PostgreSQL Requirements
 
@@ -154,6 +128,18 @@ CREATE EXTENSION pg_trgm;
 On some systems you may need to install an additional package (e.g.
 `postgresql-contrib`) for this extension to become available.
 
+## Unicorn Workers
+
+It's possible to increase the amount of unicorn workers and this will usually help to reduce the response time of the applications and increase the ability to handle parallel requests.
+
+For most instances we recommend using: CPU cores + 1 = unicorn workers.
+So for a machine with 2 cores, 3 unicorn workers is ideal.
+
+For all machines that have 2GB and up we recommend a minimum of three unicorn workers.
+If you have a 1GB machine we recommend to configure only two Unicorn workers to prevent excessive swapping.
+
+To change the Unicorn workers when you have the Omnibus package please see [the Unicorn settings in the Omnibus GitLab documentation](https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/doc/settings/unicorn.md#unicorn-settings).
+
 ## Redis and Sidekiq
 
 Redis stores all user sessions and the background task queue.
@@ -172,6 +158,26 @@ default settings.
 If you would like to disable Prometheus and it's exporters or read more information
 about it, check the [Prometheus documentation](../administration/monitoring/prometheus/index.md).
 
+## GitLab Runner
+
+We strongly advise against installing GitLab Runner on the same machine you plan
+to install GitLab on. Depending on how you decide to configure GitLab Runner and
+what tools you use to exercise your application in the CI environment, GitLab
+Runner can consume significant amount of available memory.
+
+Memory consumption calculations, that are available above, will not be valid if
+you decide to run GitLab Runner and the GitLab Rails application on the same
+machine.
+
+It is also not safe to install everything on a single machine, because of the
+[security reasons] - especially when you plan to use shell executor with GitLab
+Runner.
+
+We recommend using a separate machine for each GitLab Runner, if you plan to
+use the CI features.
+
+[security reasons]: https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/blob/master/docs/security/index.md
+
 ## Supported web browsers
 
 We support the current and the previous major release of Firefox, Chrome/Chromium, Safari and Microsoft browsers (Microsoft Edge and Internet Explorer 11).
diff --git a/doc/update/README.md b/doc/update/README.md
index d024a809f24..22dbc7c750f 100644
--- a/doc/update/README.md
+++ b/doc/update/README.md
@@ -11,22 +11,6 @@ There are currently 3 official ways to install GitLab:
 
 Based on your installation, choose a section below that fits your needs.
 
----
-
-<!-- START doctoc generated TOC please keep comment here to allow auto update -->
-<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
-**Table of Contents**  *generated with [DocToc](https://github.com/thlorenz/doctoc)*
-
-- [Omnibus Packages](#omnibus-packages)
-- [Installation from source](#installation-from-source)
-- [Installation using Docker](#installation-using-docker)
-- [Upgrading between editions](#upgrading-between-editions)
-    - [Community to Enterprise Edition](#community-to-enterprise-edition)
-    - [Enterprise to Community Edition](#enterprise-to-community-edition)
-- [Miscellaneous](#miscellaneous)
-
-<!-- END doctoc generated TOC please keep comment here to allow auto update -->
-
 ## Omnibus Packages
 
 - The [Omnibus update guide](http://docs.gitlab.com/omnibus/update/README.html)
diff --git a/doc/user/group/subgroups/index.md b/doc/user/group/subgroups/index.md
index c4921c74a17..1f4aafe27c2 100644
--- a/doc/user/group/subgroups/index.md
+++ b/doc/user/group/subgroups/index.md
@@ -1,6 +1,8 @@
 # Subgroups
 
-> [Introduced][ce-2772] in GitLab 9.0.
+>**Notes:**
+- [Introduced][ce-2772] in GitLab 9.0.
+- MySQL support for subgroups was dropped in GitLab 9.3.
 
 With subgroups (aka nested groups or hierarchical groups) you can have
 up to 20 levels of nested groups, which among other things can help you to: