Update comments and docs around min schema version

Fixed some spelling
Dropped rake task description for a prefix only task
Added note on skipping the check to the postgres debugging dev doc

doc/development/database_debugging.md

@@ -85,3 +85,21 @@ eric             37709   0.0  0.0  2518640   7524 s006  S    Wed11AM   0:00.79 s
 $ kill 87304
 $ kill 37709
 ```
+
+### db:migrate `database version is too old to be migrated` error
+
+Users receive this error when `db:migrate` detects that the current schema version
+is older than the `MIN_SCHEMA_VERSION` defined in the `Gitlab::Database` library
+module.
+
+Over time we cleanup/combine old migrations in the codebase, so it is not always
+possible to migrate GitLab from every previous version.
+
+In some cases you may want to bypass this check. For example, if you were on a version
+of GitLab schema later than the `MIN_SCHEMA_VERSION`, and then rolled back the
+to an older migration, from before. In this case, in order to migrate forward again,
+you should set the `SKIP_SCHEMA_VERSION_CHECK` environment variable.
+
+```sh
+bundle exec rake db:migrate SKIP_SCHEMA_VERSION_CHECK=true
+```

lib/gitlab/database.rb

@@ -11,7 +11,7 @@ module Gitlab
     # https://dev.mysql.com/doc/refman/5.7/en/datetime.html
     MAX_TIMESTAMP_VALUE = Time.at((1 << 31) - 1).freeze
 
-    # Minimum schema version from which migrations are be supported
+    # Minimum schema version from which migrations are supported
     # Migrations before this version may have been removed
     MIN_SCHEMA_VERSION = 20190506135400
     MIN_SCHEMA_GITLAB_VERSION = '11.11.0'

lib/tasks/migrate/schema_check.rake

 # frozen_string_literal: true
 
-desc 'Configures the database by running migrate, or by loading the schema and seeding if needed'
+# Configures the database by running migrate, or by loading the schema and seeding if needed
 task schema_version_check: :environment do
   next if ENV['SKIP_SCHEMA_VERSION_CHECK']