From 1f1aad9e50a3705a4254439189d0dbd9b5a5a91e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Martin=20Ausw=C3=B6ger?= <martin@auswoeger.com>
Date: Sun, 5 Nov 2023 20:21:38 +0100
Subject: [PATCH] Fix MariaDB list columns performance (#6202)

|      Q       |   A
|------------- | -----------
| Type         | bug
| Fixed issues | https://github.com/contao/contao/issues/6409

#### Summary

Starting with version 3.7.0 we noticed that the `listTableColumns()`
method got very slow on some systems, our migrate command went from
taking around 2 seconds with version 3.6 to 260 seconds with version3.7.

This is due to the `LEFT JOIN information_schema.CHECK_CONSTRAINTS` not
getting optimized by MariaDB which causes the database server to scan
every table of every database.

This pull request fixes that by using a subquery that is limited by
`WHERE CONSTRAINT_SCHEMA = $databaseName`. This brings the performance
back to where it was with version 3.6.
---
 src/Platforms/AbstractMySQLPlatform.php       | 12 +++++-
 src/Platforms/MariaDb1043Platform.php         | 39 ++++++++++---------
 src/Schema/MySQLSchemaManager.php             |  3 +-
 .../Schema/MySQLSchemaManagerTest.php         |  6 +++
 4 files changed, 39 insertions(+), 21 deletions(-)

diff --git a/src/Platforms/AbstractMySQLPlatform.php b/src/Platforms/AbstractMySQLPlatform.php
index d1e3e5aff52..284194d9dc7 100644
--- a/src/Platforms/AbstractMySQLPlatform.php
+++ b/src/Platforms/AbstractMySQLPlatform.php
@@ -406,7 +406,17 @@ public function getListTableColumnsSQL($table, $database = null)
      */
     public function getColumnTypeSQLSnippets(string $tableAlias = 'c'): array
     {
-        return [$tableAlias . '.COLUMN_TYPE', ''];
+        return [$this->getColumnTypeSQLSnippet(...func_get_args()), ''];
+    }
+
+    /**
+     * The SQL snippet required to elucidate a column type
+     *
+     * Returns a column type SELECT snippet string
+     */
+    public function getColumnTypeSQLSnippet(string $tableAlias = 'c', ?string $databaseName = null): string
+    {
+        return $tableAlias . '.COLUMN_TYPE';
     }
 
     /** @deprecated The SQL used for schema introspection is an implementation detail and should not be relied upon. */
diff --git a/src/Platforms/MariaDb1043Platform.php b/src/Platforms/MariaDb1043Platform.php
index 926c6b9529d..8ba6792ed01 100644
--- a/src/Platforms/MariaDb1043Platform.php
+++ b/src/Platforms/MariaDb1043Platform.php
@@ -40,7 +40,8 @@ public function getJsonTypeDeclarationSQL(array $column): string
      */
     public function getListTableColumnsSQL($table, $database = null): string
     {
-        [$columnTypeSQL, $joinCheckConstraintSQL] = $this->getColumnTypeSQLSnippets();
+        // @todo 4.0 - call getColumnTypeSQLSnippet() instead
+        [$columnTypeSQL, $joinCheckConstraintSQL] = $this->getColumnTypeSQLSnippets('c', $database);
 
         return sprintf(
             <<<SQL
@@ -72,34 +73,34 @@ public function getListTableColumnsSQL($table, $database = null): string
      * is valid json. This function generates the SQL snippets which reverse this aliasing i.e. report a column
      * as JSON where it was originally specified as such instead of LONGTEXT.
      *
-     * The CHECK constraints are stored in information_schema.CHECK_CONSTRAINTS so JOIN that table.
-     *
-     * @return array{string, string}
+     * The CHECK constraints are stored in information_schema.CHECK_CONSTRAINTS so query that table.
      */
-    public function getColumnTypeSQLSnippets(string $tableAlias = 'c'): array
+    public function getColumnTypeSQLSnippet(string $tableAlias = 'c', ?string $databaseName = null): string
     {
         if ($this->getJsonTypeDeclarationSQL([]) !== 'JSON') {
-            return parent::getColumnTypeSQLSnippets($tableAlias);
+            return parent::getColumnTypeSQLSnippet($tableAlias, $databaseName);
         }
 
-        $columnTypeSQL = <<<SQL
+        $databaseName = $this->getDatabaseNameSQL($databaseName);
+
+        // The check for `CONSTRAINT_SCHEMA = $databaseName` is mandatory here to prevent performance issues
+        return <<<SQL
             IF(
-                x.CHECK_CLAUSE IS NOT NULL AND $tableAlias.COLUMN_TYPE = 'longtext',
+                $tableAlias.COLUMN_TYPE = 'longtext'
+                AND EXISTS(
+                    SELECT * from information_schema.CHECK_CONSTRAINTS 
+                    WHERE CONSTRAINT_SCHEMA = $databaseName
+                    AND TABLE_NAME = $tableAlias.TABLE_NAME
+                    AND CHECK_CLAUSE = CONCAT(
+                        'json_valid(`',
+                            $tableAlias.COLUMN_NAME,
+                        '`)'
+                    )
+                ),
                 'json',
                 $tableAlias.COLUMN_TYPE
             )
         SQL;
-
-        $joinCheckConstraintSQL = <<<SQL
-        LEFT JOIN information_schema.CHECK_CONSTRAINTS x
-            ON (
-                $tableAlias.TABLE_SCHEMA = x.CONSTRAINT_SCHEMA
-                AND $tableAlias.TABLE_NAME = x.TABLE_NAME
-                AND x.CHECK_CLAUSE = CONCAT('json_valid(`', $tableAlias.COLUMN_NAME , '`)')
-            )
-        SQL;
-
-        return [$columnTypeSQL, $joinCheckConstraintSQL];
     }
 
     /** {@inheritDoc} */
diff --git a/src/Schema/MySQLSchemaManager.php b/src/Schema/MySQLSchemaManager.php
index 398eaf01c22..3c00d00e239 100644
--- a/src/Schema/MySQLSchemaManager.php
+++ b/src/Schema/MySQLSchemaManager.php
@@ -437,7 +437,8 @@ protected function selectTableNames(string $databaseName): Result
 
     protected function selectTableColumns(string $databaseName, ?string $tableName = null): Result
     {
-        [$columnTypeSQL, $joinCheckConstraintSQL] = $this->_platform->getColumnTypeSQLSnippets();
+        // @todo 4.0 - call getColumnTypeSQLSnippet() instead
+        [$columnTypeSQL, $joinCheckConstraintSQL] = $this->_platform->getColumnTypeSQLSnippets('c', $databaseName);
 
         $sql = 'SELECT';
 
diff --git a/tests/Functional/Schema/MySQLSchemaManagerTest.php b/tests/Functional/Schema/MySQLSchemaManagerTest.php
index 3e90d6aabed..519360928bd 100644
--- a/tests/Functional/Schema/MySQLSchemaManagerTest.php
+++ b/tests/Functional/Schema/MySQLSchemaManagerTest.php
@@ -6,6 +6,7 @@
 use Doctrine\DBAL\Platforms\AbstractMySQLPlatform;
 use Doctrine\DBAL\Platforms\AbstractPlatform;
 use Doctrine\DBAL\Platforms\MariaDb1027Platform;
+use Doctrine\DBAL\Platforms\MariaDb1043Platform;
 use Doctrine\DBAL\Schema\Schema;
 use Doctrine\DBAL\Schema\Table;
 use Doctrine\DBAL\Tests\Functional\Schema\MySQL\PointType;
@@ -401,6 +402,11 @@ public function testJsonColumnType(): void
         $table->addColumn('col_json', Types::JSON);
         $this->dropAndCreateTable($table);
 
+        // Remove the comment from the column to ensure the type is detected correctly from the check constraints.
+        if ($this->connection->getDatabasePlatform() instanceof MariaDb1043Platform) {
+            $this->connection->executeStatement('ALTER TABLE test_mysql_json CHANGE COLUMN col_json col_json JSON');
+        }
+
         $columns = $this->schemaManager->listTableColumns('test_mysql_json');
 
         self::assertSame(Types::JSON, $columns['col_json']->getType()->getName());