1 files changed, 153 insertions, 0 deletions
diff --git a/spec/lib/gitlab/database/sharding_key_spec.rb b/spec/lib/gitlab/database/sharding_key_spec.rb
new file mode 100644
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+++ b/spec/lib/gitlab/database/sharding_key_spec.rb
@@ -0,0 +1,153 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'new tables missing sharding_key', feature_category: :cell do
+  # Specific tables can be temporarily exempt from this requirement. You must add an issue link in a comment next to
+  # the table name to remove this once a decision has been made.
+  let(:allowed_to_be_missing_sharding_key) do
+    [
+      'abuse_report_assignees', # https://gitlab.com/gitlab-org/gitlab/-/issues/432365
+      'sbom_occurrences_vulnerabilities' # https://gitlab.com/gitlab-org/gitlab/-/issues/432900
+    ]
+  end
+
+  # Specific tables can be temporarily exempt from this requirement. You must add an issue link in a comment next to
+  # the table name to remove this once a decision has been made.
+  let(:allowed_to_be_missing_not_null) do
+    [
+      'labels.project_id', # https://gitlab.com/gitlab-org/gitlab/-/issues/434356
+      'labels.group_id' # https://gitlab.com/gitlab-org/gitlab/-/issues/434356
+    ]
+  end
+
+  let(:starting_from_milestone) { 16.6 }
+
+  let(:allowed_sharding_key_referenced_tables) { %w[projects namespaces organizations] }
+
+  it 'requires a sharding_key for all cell-local tables, after milestone 16.6', :aggregate_failures do
+    tables_missing_sharding_key(starting_from_milestone: starting_from_milestone).each do |table_name|
+      expect(allowed_to_be_missing_sharding_key).to include(table_name), error_message(table_name)
+    end
+  end
+
+  it 'ensures all sharding_key columns exist and reference projects, namespaces or organizations',
+    :aggregate_failures do
+    all_tables_to_sharding_key.each do |table_name, sharding_key|
+      sharding_key.each do |column_name, referenced_table_name|
+        expect(column_exists?(table_name, column_name)).to eq(true),
+          "Could not find sharding key column #{table_name}.#{column_name}"
+        expect(referenced_table_name).to be_in(allowed_sharding_key_referenced_tables)
+      end
+    end
+  end
+
+  it 'ensures all sharding_key columns are not nullable or have a not null check constraint',
+    :aggregate_failures do
+    all_tables_to_sharding_key.each do |table_name, sharding_key|
+      sharding_key.each do |column_name, _|
+        not_nullable = not_nullable?(table_name, column_name)
+        has_null_check_constraint = has_null_check_constraint?(table_name, column_name)
+
+        if allowed_to_be_missing_not_null.include?("#{table_name}.#{column_name}")
+          expect(not_nullable || has_null_check_constraint).to eq(false),
+            "You must remove `#{table_name}.#{column_name}` from allowed_to_be_missing_not_null" \
+            "since it now has a valid constraint."
+        else
+          expect(not_nullable || has_null_check_constraint).to eq(true),
+            "Missing a not null constraint for `#{table_name}.#{column_name}` . " \
+            "All sharding keys must be not nullable or have a NOT NULL check constraint"
+        end
+      end
+    end
+  end
+
+  it 'only allows `allowed_to_be_missing_sharding_key` to include tables that are missing a sharding_key',
+    :aggregate_failures do
+    allowed_to_be_missing_sharding_key.each do |exempted_table|
+      expect(tables_missing_sharding_key(starting_from_milestone: starting_from_milestone)).to include(exempted_table),
+        "`#{exempted_table}` is not missing a `sharding_key`. " \
+        "You must remove this table from the `allowed_to_be_missing_sharding_key` list."
+    end
+  end
+
+  private
+
+  def error_message(table_name)
+    <<~HEREDOC
+      The table `#{table_name}` is missing a `sharding_key` in the `db/docs` YML file.
+      Starting from GitLab #{starting_from_milestone}, we expect all new tables to define a `sharding_key`.
+
+      To choose an appropriate sharding_key for this table please refer
+      to our guidelines at https://docs.gitlab.com/ee/development/database/multiple_databases.html#defining-a-sharding-key-for-all-cell-local-tables, or consult with the Tenant Scale group.
+    HEREDOC
+  end
+
+  def tables_missing_sharding_key(starting_from_milestone:)
+    ::Gitlab::Database::Dictionary.entries.select do |entry|
+      entry.sharding_key.blank? &&
+        entry.milestone.to_f >= starting_from_milestone &&
+        ::Gitlab::Database::GitlabSchema.cell_local?(entry.gitlab_schema)
+    end.map(&:table_name)
+  end
+
+  def all_tables_to_sharding_key
+    entries_with_sharding_key = ::Gitlab::Database::Dictionary.entries.select do |entry|
+      entry.sharding_key.present?
+    end
+
+    entries_with_sharding_key.to_h do |entry|
+      [entry.table_name, entry.sharding_key]
+    end
+  end
+
+  def not_nullable?(table_name, column_name)
+    sql = <<~SQL
+    SELECT 1
+    FROM information_schema.columns
+    WHERE table_schema = 'public' AND
+    table_name = '#{table_name}' AND
+    column_name = '#{column_name}' AND
+    is_nullable = 'NO'
+    SQL
+
+    result = ApplicationRecord.connection.execute(sql)
+
+    result.count > 0
+  end
+
+  def has_null_check_constraint?(table_name, column_name)
+    # This is a heuristic query to look for all check constraints on the table and see if any of them contain a clause
+    # column IS NOT NULL. This is to match tables that will have multiple sharding keys where either of them can be not
+    # null. Such cases may look like:
+    #    (project_id IS NOT NULL) OR (group_id IS NOT NULL)
+    # It's possible that this will sometimes incorrectly find a check constraint that isn't exactly as strict as we want
+    # but it should be pretty unlikely.
+    sql = <<~SQL
+    SELECT 1
+    FROM pg_constraint
+    INNER JOIN pg_class ON pg_constraint.conrelid = pg_class.oid
+    WHERE pg_class.relname = '#{table_name}'
+    AND contype = 'c'
+    AND pg_get_constraintdef(pg_constraint.oid) ILIKE '%#{column_name} IS NOT NULL%'
+    SQL
+
+    result = ApplicationRecord.connection.execute(sql)
+
+    result.count > 0
+  end
+
+  def column_exists?(table_name, column_name)
+    sql = <<~SQL
+    SELECT 1
+    FROM information_schema.columns
+    WHERE table_schema = 'public' AND
+    table_name = '#{table_name}' AND
+    column_name = '#{column_name}';
+    SQL
+
+    result = ApplicationRecord.connection.execute(sql)
+
+    result.count > 0
+  end
+end