Update database helpers to set the current_schema

- Update all migration and schema helpers that access
pg_class, pg_index, pg_constraing and similar catalog
yables to properly set the current schema when fetching
information about database objects.
- Update ReltuplesCountStrategy.get_statistics to use
the current schema so that we don’t accidentally fetch
the statistics for a table with the same name in a
schema different than the one GitLab uses.
- Add specs to check that migration helpers do not
generate conflicts in the presence of multiple schemas
with the same object names.

changelogs/unreleased/256121-add-schema-to-migration-helpers-that-query-the-pg-catalog.yml

+---
+title: Update database helpers to set the current_schema
+merge_request: 43568
+author:
+type: fixed

lib/gitlab/database/count/reltuples_count_strategy.rb

@@ -74,8 +74,9 @@ module Gitlab
         def get_statistics(table_names, check_statistics: true)
           time = 6.hours.ago
 
-          query = PgClass.joins("LEFT JOIN pg_stat_user_tables USING (relname)")
+          query = PgClass.joins("LEFT JOIN pg_stat_user_tables ON pg_stat_user_tables.relid = pg_class.oid")
             .where(relname: table_names)
+            .where('schemaname = current_schema()')
             .select('pg_class.relname AS table_name, reltuples::bigint AS estimate')
 
           if check_statistics

lib/gitlab/database/migration_helpers.rb

@@ -994,10 +994,10 @@ into similar problems in the future (e.g. when new tables are created).
       def postgres_exists_by_name?(table, name)
         index_sql = <<~SQL
           SELECT COUNT(*)
-          FROM pg_index
-          JOIN pg_class i ON (indexrelid=i.oid)
-          JOIN pg_class t ON (indrelid=t.oid)
-          WHERE i.relname = '#{name}' AND t.relname = '#{table}'
+          FROM pg_catalog.pg_indexes
+          WHERE schemaname = #{connection.quote(current_schema)}
+            AND tablename = #{connection.quote(table)}
+            AND indexname = #{connection.quote(name)}
         SQL
 
         connection.select_value(index_sql).to_i > 0
@@ -1053,11 +1053,15 @@ into similar problems in the future (e.g. when new tables are created).
         # the table name in addition to using the constraint_name
         check_sql = <<~SQL
           SELECT COUNT(*)
-          FROM pg_constraint
-          JOIN pg_class ON pg_constraint.conrelid = pg_class.oid
-          WHERE pg_constraint.contype = 'c'
-          AND pg_constraint.conname = '#{constraint_name}'
-          AND pg_class.relname = '#{table}'
+          FROM pg_catalog.pg_constraint con
+            INNER JOIN pg_catalog.pg_class rel
+              ON rel.oid = con.conrelid
+            INNER JOIN pg_catalog.pg_namespace nsp
+              ON nsp.oid = con.connamespace
+          WHERE con.contype = 'c'
+          AND con.conname = #{connection.quote(constraint_name)}
+          AND nsp.nspname = #{connection.quote(current_schema)}
+          AND rel.relname = #{connection.quote(table)}
         SQL
 
         connection.select_value(check_sql) > 0
@@ -1284,8 +1288,9 @@ into similar problems in the future (e.g. when new tables are created).
         check_sql = <<~SQL
           SELECT c.is_nullable
           FROM information_schema.columns c
-          WHERE c.table_name = '#{table}'
-          AND c.column_name = '#{column}'
+          WHERE c.table_schema = #{connection.quote(current_schema)}
+            AND c.table_name = #{connection.quote(table)}
+            AND c.column_name = #{connection.quote(column)}
         SQL
 
         connection.select_value(check_sql) == 'YES'

lib/gitlab/database/schema_helpers.rb

@@ -32,11 +32,14 @@ module Gitlab
       def trigger_exists?(table_name, name)
         connection.select_value(<<~SQL)
           SELECT 1
-          FROM pg_trigger
-          INNER JOIN pg_class
-            ON pg_trigger.tgrelid = pg_class.oid
-          WHERE pg_class.relname = '#{table_name}'
-            AND pg_trigger.tgname = '#{name}'
+          FROM pg_catalog.pg_trigger trgr
+            INNER JOIN pg_catalog.pg_class rel
+              ON trgr.tgrelid = rel.oid
+            INNER JOIN pg_catalog.pg_namespace nsp
+              ON nsp.oid = rel.relnamespace
+          WHERE nsp.nspname = #{connection.quote(current_schema)}
+            AND rel.relname = #{connection.quote(table_name)}
+            AND trgr.tgname = #{connection.quote(name)}
         SQL
       end
 

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -1458,15 +1458,32 @@ RSpec.describe Gitlab::Database::MigrationHelpers do
         )
       end
 
-      after do
-        'DROP INDEX IF EXISTS test_index;'
-      end
-
       it 'returns true if an index exists' do
         expect(model.index_exists_by_name?(:projects, 'test_index'))
           .to be_truthy
       end
     end
+
+    context 'when an index exists for a table with the same name in another schema' do
+      before do
+        ActiveRecord::Base.connection.execute(
+          'CREATE SCHEMA new_test_schema'
+        )
+
+        ActiveRecord::Base.connection.execute(
+          'CREATE TABLE new_test_schema.projects (id integer, name character varying)'
+        )
+
+        ActiveRecord::Base.connection.execute(
+          'CREATE INDEX test_index_on_name ON new_test_schema.projects (LOWER(name));'
+        )
+      end
+
+      it 'returns false if the index does not exist in the current schema' do
+        expect(model.index_exists_by_name?(:projects, 'test_index_on_name'))
+          .to be_falsy
+      end
+    end
   end
 
   describe '#create_or_update_plan_limit' do
@@ -1921,11 +1938,17 @@ RSpec.describe Gitlab::Database::MigrationHelpers do
       ActiveRecord::Base.connection.execute(
         'ALTER TABLE projects ADD CONSTRAINT check_1 CHECK (char_length(path) <= 5) NOT VALID'
       )
-    end
 
-    after do
       ActiveRecord::Base.connection.execute(
-        'ALTER TABLE projects DROP CONSTRAINT IF EXISTS check_1'
+        'CREATE SCHEMA new_test_schema'
+      )
+
+      ActiveRecord::Base.connection.execute(
+        'CREATE TABLE new_test_schema.projects (id integer, name character varying)'
+      )
+
+      ActiveRecord::Base.connection.execute(
+        'ALTER TABLE new_test_schema.projects ADD CONSTRAINT check_2 CHECK (char_length(name) <= 5)'
       )
     end
 
@@ -1943,6 +1966,11 @@ RSpec.describe Gitlab::Database::MigrationHelpers do
       expect(model.check_constraint_exists?(:users, 'check_1'))
         .to be_falsy
     end
+
+    it 'returns false if a constraint with the same name exists for the same table in another schema' do
+      expect(model.check_constraint_exists?(:projects, 'check_2'))
+        .to be_falsy
+    end
   end
 
   describe '#add_check_constraint' do