Truncate.php

<?php

namespace Drupal\pgsql\Driver\Database\pgsql;

use Drupal\Core\Database\Query\Truncate as QueryTruncate;
// cspell:ignore MVCC

/**
 * PostgreSQL implementation of \Drupal\Core\Database\Query\Truncate.
 */
class Truncate extends QueryTruncate {
  
  /**
   * {@inheritdoc}
   */
  public function execute() : void {
    if ($this->connection
      ->inTransaction()) {
      $savepoint = $this->connection
        ->startTransaction('mimic_implicit_commit');
    }
    try {
      parent::execute();
    } catch (\Exception $e) {
      if (isset($savepoint)) {
        $savepoint->rollback();
      }
      throw $e;
    }
    if (isset($savepoint)) {
      $savepoint->commitOrRelease();
    }
  }
  
  /**
   * {@inheritdoc}
   *
   * On PostgreSQL, TRUNCATE is fully transactional: it can be rolled back
   * and does not cause an implicit commit, so there is no need to fall back
   * to the slower DELETE query when inside a transaction. TRUNCATE is much
   * faster on large tables and, unlike DELETE, does not leave dead rows
   * behind for VACUUM to clean up.
   *
   * Note that TRUNCATE takes an ACCESS EXCLUSIVE lock on the table that is
   * held until the transaction ends, and it is not MVCC-safe with respect to
   * concurrent transactions using a snapshot taken before the truncation.
   *
   * @see https://www.postgresql.org/docs/current/sql-truncate.html
   */
  public function __toString() {
    // Create a sanitized comment string to prepend to the query.
    $comments = $this->connection
      ->makeComment($this->comments);
    return $comments . 'TRUNCATE {' . $this->connection
      ->escapeTable($this->table) . '} ';
  }

}