Document database review process

See https://gitlab.com/gitlab-com/gl-infra/infrastructure/issues/6069

.gitlab/CODEOWNERS

@@ -9,8 +9,12 @@
 app/assets/ @ClemMakesApps @fatihacet @filipa @iamphill @mikegreiling @timzallmann @kushalpandya @pslaughter
 *.scss @annabeldunstone @ClemMakesApps @fatihacet @filipa @iamphill @mikegreiling @timzallmann @kushalpandya @pslaughter
 
-# Someone from the database team should review changes in `db/`
+# Maintainers from the Database team should review changes in `db/`
 db/ @abrandl @NikolayS
+lib/gitlab/background_migration/ @abrandl @NikolayS
+lib/gitlab/database/ @abrandl @NikolayS
+lib/gitlab/sql/ @abrandl @NikolayS
+/ee/db/ @abrandl @NikolayS
 
 # Feature specific owners
 /ee/lib/gitlab/code_owners/ @reprazent

.gitlab/merge_request_templates/Database changes.md

@@ -39,20 +39,11 @@ When adding tables:
 
 - [ ] Ordered columns based on the [Ordering Table Columns](https://docs.gitlab.com/ee/development/ordering_table_columns.html#ordering-table-columns) guidelines
 - [ ] Added foreign keys to any columns pointing to data in other tables
-- [ ] Added indexes for fields that are used in statements such as WHERE, ORDER BY, GROUP BY, and JOINs
+- [ ] Added indexes for fields that are used in statements such as `WHERE`, `ORDER BY`, `GROUP BY`, and `JOIN`s
 
 When removing columns, tables, indexes or other structures:
 
 - [ ] Removed these in a post-deployment migration
 - [ ] Made sure the application no longer uses (or ignores) these structures
 
-## General checklist
+/label ~database ~"database::review pending"
-
-- [ ] [Changelog entry](https://docs.gitlab.com/ee/development/changelog.html) added, if necessary
-- [ ] [Documentation created/updated](https://docs.gitlab.com/ee/development/documentation/)
-- [ ] [Tests added for this feature/bug](https://docs.gitlab.com/ee/development/testing_guide/index.html)
-- [ ] Conforms to the [code review guidelines](https://docs.gitlab.com/ee/development/code_review.html)
-- [ ] Conforms to the [merge request performance guidelines](https://docs.gitlab.com/ee/development/merge_request_performance_guidelines.html)
-- [ ] Conforms to the [style guides](https://docs.gitlab.com/ee/development/contributing/style_guides.html)
-
-/label ~database

danger/database/Dangerfile

@@ -8,6 +8,21 @@ updated too (unless the migration isn't changing the DB schema
 and isn't the most recent one).
 MSG
 
+DB_MESSAGE = <<~MSG
+This merge request requires a database review. To make sure these
+changes are reviewed, take the following steps:
+
+1. Ensure the merge request has ~database and ~"database::review pending" labels.
+   If the merge request modifies database files, Danger will do this for you.
+1. Use the [Database changes checklist](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/.gitlab/merge_request_templates/Database%20changes.md)
+   template or add the appropriate items to the MR description.
+1. Assign and mention the database reviewer suggested by Reviewer Roulette.
+MSG
+
+DB_FILES_MESSAGE = <<~MSG
+The following files require a review from the Database team:
+MSG
+
 non_geo_db_schema_updated = !git.modified_files.grep(%r{\Adb/schema\.rb}).empty?
 geo_db_schema_updated = !git.modified_files.grep(%r{\Aee/db/geo/schema\.rb}).empty?
 
@@ -24,27 +39,18 @@ end
 
 db_paths_to_review = helper.changes_by_category[:database]
 
-unless db_paths_to_review.empty?
+if gitlab.mr_labels.include?('database') || db_paths_to_review.any?
   message 'This merge request adds or changes files that require a ' \
-    'review from the Database team.'
+    'review from the [Database team](https://gitlab.com/groups/gl-database/-/group_members).'
 
-  markdown(<<~MARKDOWN.strip)
+  markdown(DB_MESSAGE)
-## Database Review
+  markdown(DB_FILES_MESSAGE + helper.markdown_list(db_paths_to_review)) if db_paths_to_review.any?
 
-The following files require a review from the Database team:
+  database_labels = helper.missing_database_labels(gitlab.mr_labels)
 
-* #{db_paths_to_review.map { |path| "`#{path}`" }.join("\n* ")}
+  if database_labels.any?
-
+    gitlab.api.update_merge_request(gitlab.mr_json['project_id'],
-To make sure these changes are reviewed, take the following steps:
+                                        gitlab.mr_json['iid'],
-
+                                        labels: (gitlab.mr_labels + database_labels).join(','))
-1. Edit your merge request, and add `gl-database` to the list of Group
-   approvers.
-1. Mention `@gl-database` in a separate comment, and explain what needs to be
-   reviewed by the team. Please don't mention the team until your changes are
-   ready for review.
-  MARKDOWN
-
-  unless gitlab.mr_labels.include?('database')
-    warn 'This merge request is missing the ~database label.'
   end
 end

danger/roulette/Dangerfile

@@ -55,22 +55,15 @@ def spin_for_category(team, project, category, branch_name)
   "| #{helper.label_for_category(category)} | #{reviewer&.markdown_name || NO_REVIEWER} | #{maintainer&.markdown_name || NO_MAINTAINER} |"
 end
 
-def build_list(items)
-  list = items.map { |filename| "* `#{filename}`" }.join("\n")
-
-  if items.size > 10
-    "\n<details>\n\n#{list}\n\n</details>"
-  else
-    list
-  end
-end
-
 changes = helper.changes_by_category
 
 # Ignore any files that are known but uncategorized. Prompt for any unknown files
 changes.delete(:none)
 categories = changes.keys - [:unknown]
 
+# Ensure to spin for database reviewer/maintainer when ~database is applied (e.g. to review SQL queries)
+categories << :database if gitlab.mr_labels.include?('database') && !categories.include?(:database)
+
 # Single codebase MRs are reviewed using a slightly different process, so we
 # disable the review roulette for such MRs.
 # CSS Clean up MRs are reviewed using a slightly different process, so we
@@ -95,5 +88,5 @@ if changes.any? && !gitlab.mr_labels.include?('single codebase') && !gitlab.mr_l
 
   markdown(MESSAGE)
   markdown(CATEGORY_TABLE_HEADER + rows.join("\n")) unless rows.empty?
-  markdown(UNKNOWN_FILES_MESSAGE + build_list(unknown)) unless unknown.empty?
+  markdown(UNKNOWN_FILES_MESSAGE + helper.markdown_list(unknown)) unless unknown.empty?
 end

doc/development/README.md

@@ -17,6 +17,7 @@ description: 'Learn how to contribute to GitLab.'
 - [GitLab core team & GitLab Inc. contribution process](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/PROCESS.md)
 - [Generate a changelog entry with `bin/changelog`](changelog.md)
 - [Code review guidelines](code_review.md) for reviewing code and having code reviewed
+- [Database review guidelines](database_review.md) for reviewing database-related changes and complex SQL queries
 - [Automatic CE->EE merge](automatic_ce_ee_merge.md)
 - [Guidelines for implementing Enterprise Edition features](ee_features.md)
 - [Security process for developers](https://gitlab.com/gitlab-org/release/docs/blob/master/general/security/developer.md#security-releases-critical-non-critical-as-a-developer)

doc/development/code_review.md

@@ -62,6 +62,7 @@ from teams other than your own.
    **approved by a [backend maintainer](https://about.gitlab.com/handbook/engineering/projects/#gitlab-ce_maintainers_backend)**.
 1. If your merge request includes database migrations or changes to expensive queries [^2], it must be
    **approved by a [database maintainer](https://about.gitlab.com/handbook/engineering/projects/#gitlab-ce_maintainers_database)**.
+   Read the [database review guidelines](database_review.md) for more details.
 1. If your merge request includes frontend changes [^1], it must be
    **approved by a [frontend maintainer](https://about.gitlab.com/handbook/engineering/projects/#gitlab-ce_maintainers_frontend)**.
 1. If your merge request includes UX changes [^1], it must be

doc/development/contributing/merge_request_workflow.md

@@ -103,7 +103,8 @@ If you would like quick feedback on your merge request feel free to mention some
 from the [core team](https://about.gitlab.com/community/core-team/) or one of the
 [merge request coaches](https://about.gitlab.com/team/). When having your code reviewed
 and when reviewing merge requests, please keep the [code review guidelines](../code_review.md)
-in mind.
+in mind. And if your code also makes changes to the database, or does expensive queries,
+check the [database review guidelines](../database_review.md).
 
 ### Keep it simple
 

doc/development/database_review.md

@@ -0,0 +1,101 @@
+# Database Review Guidelines
+
+This page is specific to database reviews. Please refer to our
+[code review guide](code_review.md) for broader advice and best
+practices for code review in general.
+
+## General process
+
+A database review is required for:
+
+- Changes that touch the database schema or perform data migrations,
+  including files in:
+  - `db/`
+  - `lib/gitlab/background_migration/`
+- Changes to the database tooling, e.g.:
+  - migration or ActiveRecord helpers in `lib/gitlab/database/`
+  - load balancing
+- Changes that produce SQL queries that are beyond the obvious. It is
+  generally up to the author of a merge request to decide whether or
+  not complex queries are being introduced and if they require a
+  database review.
+
+A database reviewer is expected to look out for obviously complex
+queries in the change and review those closer. If the author does not
+point out specific queries for review and there are no obviously
+complex queries, it is enough to concentrate on reviewing the
+migration only.
+
+It is preferable to review queries in SQL form and generally accepted
+to ask the author to translate any ActiveRecord queries in SQL form
+for review.
+
+### Roles and process
+
+A Merge Request author's role is to:
+
+- Decide whether a database review is needed.
+- If database review is needed, add the ~database label.
+- Use the [database changes](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/.gitlab/merge_request_templates/Database%20changes.md)
+  merge request template, or include the appropriate items in the MR description.
+
+A database **reviewer**'s role is to:
+
+- Perform a first-pass review on the MR and suggest improvements to the author.
+- Once satisfied, relabel the MR with ~"database::reviewed", approve it, and
+  reassign MR to the database **maintainer** suggested by Reviewer
+  Roulette.
+
+A database **maintainer**'s role is to:
+
+- Perform the final database review on the MR.
+- Discuss further improvements or other relevant changes with the
+  database reviewer and the MR author.
+- Finally approve the MR and relabel the MR with ~"database::approved"
+- Merge the MR if no other approvals are pending or pass it on to
+  other maintainers as required (frontend, backend, docs).
+
+### Distributing review workload
+
+Review workload is distributed using [reviewer roulette](code_review.md#reviewer-roulette)
+([example](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/25181#note_147551725)).
+The MR author should then co-assign the suggested database
+**reviewer**. When they give their sign-off, they will hand over to
+the suggested database **maintainer**.
+
+If reviewer roulette didn't suggest a database reviewer & maintainer,
+make sure you have applied the ~database label and rerun the
+`danger-review` CI job, or pick someone from the
+[`@gl-database` team](https://gitlab.com/groups/gl-database/-/group_members).
+
+### How to review for database
+
+- Check migrations
+  - Review relational modeling and design choices
+  - Review migrations follow [database migration style guide](migration_style_guide.md),
+    for example
+    - [Check ordering of columns](ordering_table_columns.md)
+    - [Check indexes are present for foreign keys](migration_style_guide.md#adding-foreign-key-constraints)
+  - Ensure that migrations execute in a transaction or only contain
+    concurrent index/foreign key helpers (with transactions disabled)
+  - Check consistency with `db/schema.rb` and that migrations are [reversible](migration_style_guide.md#reversibility)
+  - For data migrations, establish a time estimate for execution
+- Check post deploy migration
+  - Make sure we can expect post deploy migrations to finish within 1 hour max.
+- Check background migrations
+  - Review queries (for example, make sure batch sizes are fine)
+  - Establish a time estimate for execution
+- Query performance
+  - Check for any obviously complex queries and queries the author specifically
+    points out for review (if any)
+  - If not present yet, ask the author to provide SQL queries and query plans
+    (e.g. by using [chatops](understanding_explain_plans.md#chatops) or direct
+    database access)
+  - For given queries, review parameters regarding data distribution
+  - [Check query plans](understanding_explain_plans.md) and suggest improvements
+    to queries (changing the query, schema or adding indexes and similar)
+  - General guideline is for queries to come in below 100ms execution time
+  - If queries rely on prior migrations that are not present yet on production
+    (eg indexes, columns), you can use a [one-off instance from the restore
+    pipeline](https://ops.gitlab.net/gitlab-com/gl-infra/gitlab-restore/postgres-gprd)
+    in order to establish a proper testing environment.

lib/gitlab/danger/helper.rb

@@ -46,6 +46,16 @@ module Gitlab
         ee? ? 'gitlab-ee' : 'gitlab-ce'
       end
 
+      def markdown_list(items)
+        list = items.map { |item| "* `#{item}`" }.join("\n")
+
+        if items.size > 10
+          "\n<details>\n\n#{list}\n\n</details>\n"
+        else
+          list
+        end
+      end
+
       # @return [Hash<String,Array<String>>]
       def changes_by_category
         all_changed_files.each_with_object(Hash.new { |h, k| h[k] = [] }) do |file, hash|
@@ -132,6 +142,22 @@ module Gitlab
       def new_teammates(usernames)
         usernames.map { |u| Gitlab::Danger::Teammate.new('username' => u) }
       end
+
+      def missing_database_labels(current_mr_labels)
+        labels = if has_database_scoped_labels?(current_mr_labels)
+                   ['database']
+                 else
+                   ['database', 'database::review pending']
+                 end
+
+        labels - current_mr_labels
+      end
+
+      private
+
+      def has_database_scoped_labels?(current_mr_labels)
+        current_mr_labels.any? { |label| label.start_with?('database::') }
+      end
     end
   end
 end

spec/lib/gitlab/danger/helper_spec.rb

@@ -85,6 +85,20 @@ describe Gitlab::Danger::Helper do
     end
   end
 
+  describe '#markdown_list' do
+    it 'creates a markdown list of items' do
+      items = %w[a b]
+
+      expect(helper.markdown_list(items)).to eq("* `a`\n* `b`")
+    end
+
+    it 'wraps items in <details> when there are more than 10 items' do
+      items = ('a'..'k').to_a
+
+      expect(helper.markdown_list(items)).to match(%r{<details>[^<]+</details>})
+    end
+  end
+
   describe '#changes_by_category' do
     it 'categorizes changed files' do
       expect(fake_git).to receive(:added_files) { %w[foo foo.md foo.rb foo.js db/foo lib/gitlab/database/foo.rb qa/foo ee/changelogs/foo.yml] }
@@ -224,4 +238,20 @@ describe Gitlab::Danger::Helper do
       expect(teammates.map(&:username)).to eq(usernames)
     end
   end
+
+  describe '#missing_database_labels' do
+    subject { helper.missing_database_labels(current_mr_labels) }
+
+    context 'when current merge request has ~database::review pending' do
+      let(:current_mr_labels) { ['database::review pending', 'feature'] }
+
+      it { is_expected.to match_array(['database']) }
+    end
+
+    context 'when current merge request does not have ~database::review pending' do
+      let(:current_mr_labels) { ['feature'] }
+
+      it { is_expected.to match_array(['database', 'database::review pending']) }
+    end
+  end
 end