Mention PG upgrade

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/233915

doc/development/architecture.md

@@ -259,7 +259,7 @@ Consul is a tool for service discovery and configuration. Consul is distributed,
 - Configuration:
   - [Omnibus](https://docs.gitlab.com/omnibus/settings/database.html#disabling-automatic-database-migration)
   - [Charts](https://docs.gitlab.com/charts/charts/gitlab/migrations/)
-  - [Source](../update/upgrading_from_source.md#13-install-libraries-migrations-etc)
+  - [Source](../update/upgrading_from_source.md#14-install-libraries-migrations-etc)
 - Layer: Core Service (Data)
 
 #### Elasticsearch
@@ -555,7 +555,7 @@ Redis is packaged to provide a place to store:
 
 - [Project page](https://github.com/docker/distribution/blob/master/README.md)
 - Configuration:
-  - [Omnibus](../update/upgrading_from_source.md#13-install-libraries-migrations-etc)
+  - [Omnibus](../update/upgrading_from_source.md#14-install-libraries-migrations-etc)
   - [Charts](https://docs.gitlab.com/charts/charts/registry/)
   - [Source](../administration/packages/container_registry.md#enable-the-container-registry)
   - [GDK](https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/howto/registry.md)

doc/update/upgrading_from_source.md

@@ -164,7 +164,16 @@ sudo make prefix=/usr/local install
 # You should edit config/gitlab.yml, change the git -> bin_path to /usr/local/bin/git
 ```
 
-### 7. Get latest code
+### 7. Update PostgreSQL
+
+CAUTION: **Caution:**
+From GitLab 13.0, you must use at least PostgreSQL 11.
+
+The latest version of GitLab might depend on a more recent PostgreSQL version than what you are currently running (see the [PostgreSQL requirements](../install/requirements.md#postgresql-requirements)).
+
+In order to upgrade PostgreSQL, please refer to its [documentation](https://www.postgresql.org/docs/11/upgrading.html).
+
+### 8. Get latest code
 
 ```shell
 cd /home/git/gitlab
@@ -192,7 +201,7 @@ cd /home/git/gitlab
 sudo -u git -H git checkout BRANCH-ee
 ```
 
-### 8. Update GitLab Shell
+### 9. Update GitLab Shell
 
 ```shell
 cd /home/git/gitlab-shell
@@ -202,7 +211,7 @@ sudo -u git -H git checkout v$(</home/git/gitlab/GITLAB_SHELL_VERSION)
 sudo -u git -H make build
 ```
 
-### 9. Update GitLab Workhorse
+### 10. Update GitLab Workhorse
 
 Install and compile GitLab Workhorse. GitLab Workhorse uses
 [GNU Make](https://www.gnu.org/software/make/).
@@ -217,7 +226,7 @@ sudo -u git -H git checkout v$(</home/git/gitlab/GITLAB_WORKHORSE_VERSION)
 sudo -u git -H make
 ```
 
-### 10. Update Gitaly
+### 11. Update Gitaly
 
 #### Compile Gitaly
 
@@ -228,7 +237,7 @@ sudo -u git -H git checkout v$(</home/git/gitlab/GITALY_SERVER_VERSION)
 sudo -u git -H make
 ```
 
-### 11. Update GitLab Pages
+### 12. Update GitLab Pages
 
 #### Only needed if you use GitLab Pages
 
@@ -245,7 +254,7 @@ sudo -u git -H git checkout v$(</home/git/gitlab/GITLAB_PAGES_VERSION)
 sudo -u git -H make
 ```
 
-### 12. Update configuration files
+### 13. Update configuration files
 
 #### New configuration options for `gitlab.yml`
 
@@ -318,7 +327,7 @@ For Ubuntu 16.04.1 LTS:
 sudo systemctl daemon-reload
 ```
 
-### 13. Install libraries, migrations, etc
+### 14. Install libraries, migrations, etc
 
 ```shell
 cd /home/git/gitlab
@@ -342,14 +351,14 @@ sudo -u git -H bundle exec rake yarn:install gitlab:assets:clean gitlab:assets:c
 sudo -u git -H bundle exec rake cache:clear RAILS_ENV=production
 ```
 
-### 14. Start application
+### 15. Start application
 
 ```shell
 sudo service gitlab start
 sudo service nginx restart
 ```
 
-### 15. Check application status
+### 16. Check application status
 
 Check if GitLab and its environment are configured correctly: