Deadlock handling

Rationale

Deadlocks are a very special case in database systems and often need special programmatic handling.

Inheritance

 lang.Throwable
 `- lang.XPException
    `- rdbms.SQLException
       `- rdbms.SQLStatementFailedException
          `- rdbms.SQLDeadlockException

Example (current usage)

  $conn= DriverManager::getConnection('sybase://...');
  
  try {
    $tran= $conn->begin(new Transaction('update'));
    $conn->query('...');
    $conn->query('...');
  } catch (SQLStatementFailedException $e) {
    if (1205 == $e->getErrorcode()) {
      // Handle deadlock
    } else {
      $tran && $tran->rollback();
      // Handle other statement errors
    }
  } catch (SQLException $e) {
    $tran && $tran->rollback();
    // Handle other errors
  }

Problems with this approach:

• The error code is driver-specific
• Complicated sourcecode

Sybase

• Error code: 1205
• Can be retrieved by: sybase_query('select @@error')

MySQL

• Error code: 1213 (SQLSTATE: 40001 (ER_LOCK_DEADLOCK))
• Can be retrieved by: mysql_errno()

PostgreSQL

• Error code: 40P01 DEADLOCK DETECTED
• Can be retrieved by: pg_result_status() / pg_result_error_field()

Example (new functionality)

  $conn= DriverManager::getConnection('sybase://...');
  
  try {
    $tran= $conn->begin(new Transaction('update'));
    $conn->query('...');
    $conn->query('...');
  } catch (SQLDeadlockException $e) {
    // Handle deadlock
  } catch (SQLException $e) {
    $tran && $tran->rollback();
    // Handle other situations
  }

n/a

Neglectible.

n/a

- http://www.xaprb.com/blog/2006/08/08/how-to-deliberately-cause-a-deadlock-in-mysql/ - http://www.blacksheepnetworks.com/security/resources/bossconsulting/sybase_dba/sublevels/deadlock.info - http://www.compuspec.net/reference/database/sybase/deadlock.shtml - http://xp-framework.net/rfc/contrib/rfc0159.diff

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