The nested transaction example here is great, but it's missing a key piece of the puzzle.  Commits will commit everything, I only wanted commits to actually commit when the outermost commit has been completed.  This can be done in InnoDB with savepoints.

<?php

class Database extends PDO
{

    protected $transactionCount = 0;

    public function beginTransaction()
    {
        if (!$this->transactionCounter++) {
            return parent::beginTransaction();
        }
        $this->exec('SAVEPOINT trans'.$this->transactionCounter);
        return $this->transactionCounter >= 0;
    }

    public function commit()
    {
        if (!--$this->transactionCounter) {
            return parent::commit();
        }
        return $this->transactionCounter >= 0;
    }

    public function rollback()
    {
        if (--$this->transactionCounter) {
            $this->exec('ROLLBACK TO trans'.$this->transactionCounter + 1);
            return true;
        }
        return parent::rollback();
    }
    
}

You can generate problems with nested beginTransaction and commit calls.
example:

beginTransaction()
do imprortant stuff
call method
    beginTransaction()
    basic stuff 1
    basic stuff 2
    commit()
do most important stuff
commit()

Won't work and is dangerous since you could close your transaction too early with the nested commit().

There is no need to mess you code and pass like a bool which indicate if transaction is already running. You could just overload the beginTransaction() and commit() in your PDO wrapper like this:

<?php
class Database extends \\PDO
{
    protected $transactionCounter = 0;
    function beginTransaction()
    {
        if(!$this->transactionCounter++)
            return parent::beginTransaction();
       return $this->transactionCounter >= 0;
    }

    function commit()
    {
       if(!--$this->transactionCounter)
           return parent::commit();
       return $this->transactionCounter >= 0;
    }

    function rollback()
    {
        if($this->transactionCounter >= 0)
        {
            $this->transactionCounter = 0;
            return parent::rollback();
        }
        $this->transactionCounter = 0;
        return false;
    }
//...
}
?>

If you are using PDO::SQLITE and need to support a high level of concurrency with locking, try preparing your statements prior to calling beginTransaction() and you may also need to call closeCursor() on SELECT statements to prevent the driver from thinking that there are open transactions.

Here's an example (Windows, PHP version 5.2.8).  We test this by opening 2 browser tabs to this script and running them at the same time.  If we put the beginTransaction before the prepare, the second browser tab would hit the catch block and the commit would throw another PDOException indicating that transactions were still open.

<?php
$conn = new PDO('sqlite:C:\path\to\file.sqlite');
$stmt = $conn->prepare('INSERT INTO my_table(my_id, my_value) VALUES(?, ?)');
$waiting = true; // Set a loop condition to test for
while($waiting) {
    try {
        $conn->beginTransaction();
        for($i=0; $i < 10; $i++) {
            $stmt->bindValue(1, $i, PDO::PARAM_INT);
            $stmt->bindValue(2, 'TEST', PDO::PARAM_STR);
            $stmt->execute();
            sleep(1);
        }
        $conn->commit();
        $waiting = false;
    } catch(PDOException $e) {
        if(stripos($e->getMessage(), 'DATABASE IS LOCKED') !== false) {
            // This should be specific to SQLite, sleep for 0.25 seconds
            // and try again.  We do have to commit the open transaction first though
            $conn->commit();
            usleep(250000);
        } else {
            $conn->rollBack();
            throw $e;
        }
    }
}

?>

please fix in answer #116669:

    $this->exec('ROLLBACK TO trans'.$this->transactionCounter + 1);

with

    $this->exec('ROLLBACK TO trans'.($this->transactionCounter + 1));

In response to "Anonymous / 20-Dec-2007 03:04"

You could also extend the PDO class and hold a private flag to check if a transaction is already started.

class MyPDO extends PDO {
   protected $hasActiveTransaction = false;

   function beginTransaction () {
      if ( $this->hasActiveTransaction ) {
         return false;
      } else {
         $this->hasActiveTransaction = parent::beginTransaction ();
         return $this->hasActiveTransaction;
      }
   }

   function commit () {
      parent::commit ();
      $this->hasActiveTransaction = false;
   }

   function rollback () {
      parent::rollback ();
      $this->hasActiveTransaction = false;
   }

}

A way to use transaction and prepared statement to speed-up bulk INSERTs :

<?php

// ...

$insert = $pdo->prepare('INSERT INTO table (c1, c2, c3) VALUES (?, ?, ?)');
$bulk = 3_000; // To adjust according to your data/system
$rows = 0;

$pdo->beginTransaction();
while ($entry = fgetcsv($fp)) {
    $insert->execute($entry);
    if (++$rows % $bulk === 0) {
        $pdo->commit();
        $pdo->beginTransaction();
    }
}
if ($pdo->inTransaction()) { // Remaining rows insertion
    $pdo->commit();
}

OK I'm finding a solution for "NESTED" transactions in MySQL, and as you know in the MySQL documentation says that it's not possible to have transactions within transactions. I was trying to use the Database class propossed here in http://php.net/manual/en/pdo.begintransaction.php but unfortunately that's wrong for many things related to the control flow that I have been solved with the following code (LOOK THE EXAMPLE AT THE END, CarOwner)

<?php

class TransactionController extends \\PDO {
    public static $warn_rollback_was_thrown = false;
    public static $transaction_rollbacked = false;
    public function __construct()
    {
        parent :: __construct( ... connection info ... );
    }
    public static $nest = 0;
    public function reset()
    {
        TransactionController :: $transaction_rollbacked = false;
        TransactionController :: $warn_rollback_was_thrown = false;
        TransactionController :: $nest = 0;
    }
    function beginTransaction()
    {
        $result = null;
        if (TransactionController :: $nest == 0) {
            $this->reset();
            $result = $this->beginTransaction();
        }
        TransactionController :: $nest++;
        return $result;
    }

    public function commit()
    {

        $result = null;

        if (TransactionController :: $nest == 0 &&
                !TransactionController :: $transaction_rollbacked &&
                !TransactionController :: $warn_rollback_was_thrown) {
                    $result = parent :: commit();
                }
                TransactionController :: $nest--;
                return $result;
    }

    public function rollback()
    {
        $result = null;
        if (TransactionController :: $nest >= 0) {
            if (TransactionController :: $nest == 0) {
                $result = parent :: rollback();
                TransactionController :: $transaction_rollbacked = true;
            }
            else {
                TransactionController  :: $warn_rollback_was_thrown = true;
            }
        }
        TransactionController :: $nest--;
        return $result;
    }

    public function transactionFailed()
    {
        return TransactionController :: $warn_rollback_was_thrown === true;
    }
    // to force rollback you can only do it from $nest = 0
    public function forceRollback()
    {
        if (TransactionController :: $nest === 0) {
            throws new \PDOException();
        }
    }
}

?>

be aware that you also can not use TRUNCATE TABLE as this statement will trigger a commit just like CREATE TABLE or DROP TABLE

it is best to only use SELECT, UPDATE and DELETE within a transaction, all other statements may cause commits thus breaking the atomicity of your transactions and their ability to rollback

obviously you can use DELETE FROM <table> instead of TRUNCATE TABLE but be aware that there are differences between both statements, for example TRUNCATE resets the auto_increment value while DELETE does not.

// If you need to set an ISOLATION level or LOCK MODE it needs to be done BEFORE you make the BeginTransaction() call...
//
//  **note** you should always check result codes on operations and do error handling.  This sample code
//  assumes all the calls work so that the order of operations is accurate and easy to see
//
//  THIS IS using the PECL PDO::INFORMIX module, running on fedora core 6, php 5.2.4
//
//    This is the correct way to address an informix -243 error (could not position within table) when there
//    is no ISAM error indicating a table corruption.  A -243 can happen (if the table/indexes, etc., are ok) 
//    if a row is locked.  The code below sets the LOCK MODE to wait 2 minutes (120 seconds) before
//    giving up.  In this example you get READ COMMITTED rows, if you don't need read committed
//    but just need to get whatever data is there (ignoring locked rows, etc.) instead of
//    "SET LOCK MODE TO WAIT 120" you could "SET ISOLATION TO DIRTY READ".
//
//    In informix you *must* manage how you do reads because it is very easy to trigger a
//    lock table overflow (which downs the instance) if you have lots of rows, are using joins
//    and have many updates happening.  
//

// e.g.,

$sql= "SELECT FIRST 50 * FROM mytable WHERE mystuff=1 ORDER BY myid";                    /* define SQL query */

try                                                                                /* create an exception handler */
    {
    $dbh = new PDO("informix:host=......");
         
    if ($dbh)    /* did we connect? */
        {
        $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        $dbh->query("SET LOCK MODE TO WAIT 120")
        
        # ----------------
        # open transaction cursor
        # ----------------
        if    ( $dbh->beginTransaction() )                                         # explicitly open cursor
            {
            try    /* open exception handler */
                {
                $stmt = $dbh->prepare($sql, array(PDO::ATTR_CURSOR => PDO::CURSOR_SCROLL));

                $stmt->execute();
                
                while ($row = $stmt->fetch(PDO::FETCH_NUM, PDO::FETCH_ORI_NEXT))
                    {
                    $data = $row[0] . "\t" . $row[1] . "\t" . $row[2] . "\t" . $row[3] . "\t" . $row[4] . "\t" . $row[5] . "\t" . $row[6] . "\t" . $row[7] . "\n" . $row[8] ;
                    //print $data;
                    print_r($row);
                    };
                
                $stmt = null;
                }
            catch (PDOException $e)
                {
                print "Query Failed!\n\n";
                
                print "DBA FAIL:" . $e->getMessage();
                };
            
            $dbh->rollback();                                                       # abort any changes (ie. $dbh->commit()
            $dbh = null;                                                            # close connection
            }
        else
            {
            # we should never get here, it should go to the exception handler
            print "Unable to establish connection...\n\n";
            };
        };
    }
catch (Exception $e)
    {
    $dbh->rollback();
    echo "Failed: " . $e->getMessage();
    };

The example is misleading, Typically data definition language clauses (DDL) will trigger the database engine to automatically commit. It means that if you drop a table, that query will be executed regardless of the transaction.
Ref-Mysql:
    http://dev.mysql.com/doc/refman/5.0/en/implicit-commit.html