It's worth noting that you can perform transactions without disabling autocommit just using standard sql. "START TRANSACTION;" will start a transaction. "COMMIT;" will commit the results and "ROLLBACK;" will revert to the pre-transaction state.
CREATE TABLE and CREATE DATABASE (and probably others) are always commited immediately and your transaction appears to terminate. Thus any commands before and after will be commited, even if a subsequent rollback is attempted.
If you are in the middle of a transaction and you call mysqli_close() it appears that you get the funcitonality of an implicit rollback.
I can't reproduce the "code bug causes lock" problem outlined below (I always get a successful rollback and the script will run umtine times successfully). Therefore, I would suggest that the problem is fixed in php-5.2.2.
mysqli::autocommit
mysqli_autocommit
(PHP 5, PHP 7)
mysqli::autocommit -- mysqli_autocommit — Aktiviert oder deaktiviert das automatische Übertragen von Datenbankänderungen
Beschreibung
Objektorientierter Stil
public mysqli::autocommit
( bool
$enable
) : boolProzeduraler Stil
Aktiviert oder deaktiviert den Autocommit-Modus für Abfragen an die Datenbankverbindung.
Um den aktuellen Status von Autocommit festzustellen, ist die SQL-Anweisung
SELECT @@autocommit zu verwenden.
Parameter-Liste
-
link -
Nur bei prozeduralem Aufruf: Ein von mysqli_connect() oder mysqli_init() zurückgegebenes Verbindungsobjekt.
-
enable -
Legt fest, ob Autocommit aktiviert werden soll oder nicht.
Rückgabewerte
Gibt bei Erfolg true zurück. Im Fehlerfall wird false zurückgegeben.
Anmerkungen
Hinweis:
Die Funktion kann nicht mit Tabellentypen verwendet werden, die keine Transaktionen unterstützen (wie MyISAM oder ISAM).
Beispiele
Beispiel #1 mysqli::autocommit()-Beispiel
Objektorientierter Stil
<?php
/* mysqli anweisen, eine Exception auszulösen, wenn ein Fehler auftritt */
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");
/* Die Tabellen-Engine muss Transaktionen unterstützen */
$mysqli->query("CREATE TABLE IF NOT EXISTS language (
Code text NOT NULL,
Speakers int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;");
/* autocommit ausschalten */
$mysqli->autocommit(false);
$result = $mysqli->query("SELECT @@autocommit");
$row = $result->fetch_row();
printf("Autocommit ist %s\n", $row[0]);
try {
/* Insert-Anweisung vorbereiten */
$stmt = $mysqli->prepare('INSERT INTO language(Code, Speakers) VALUES (?,?)');
$stmt->bind_param('ss', $language_code, $native_speakers);
/* Ein paar Werte einfügen */
$language_code = 'DE';
$native_speakers = 50_123_456;
$stmt->execute();
$language_code = 'FR';
$native_speakers = 40_546_321;
$stmt->execute();
/* Übertragung der Daten in die Datenbank. Dies setzt nicht autocommit=true */
$mysqli->commit();
print "2 Datensätze in die Datenbank übertragen\n";
$result = $mysqli->query("SELECT @@autocommit");
$row = $result->fetch_row();
printf("Autocommit ist %s\n", $row[0]);
/* Versuchen, weitere Werte einzufügen */
$language_code = 'PL';
$native_speakers = 30_555_444;
$stmt->execute();
$language_code = 'DK';
$native_speakers = 5_222_444;
$stmt->execute();
/* Das Setzen von autocommit=true löst eine Übertragung aus */
$mysqli->autocommit(true);
print "2 weitere Datensätze in die Datenbank übertragen\n";
} catch (mysqli_sql_exception $exception) {
$mysqli->rollback();
throw $exception;
}
Prozeduraler Stil
<?php
/* mysqli anweisen, eine Exception auszulösen, wenn ein Fehler auftritt */
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = mysqli_connect("localhost", "my_user", "my_password", "world");
/* Die Tabellen-Engine muss Transaktionen unterstützen */
mysqli_query($mysqli, "CREATE TABLE IF NOT EXISTS language (
Code text NOT NULL,
Speakers int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;");
/* autocommit ausschalten */
mysqli_autocommit($mysqli, false);
$result = mysqli_query($mysqli, "SELECT @@autocommit");
$row = mysqli_fetch_row($result);
printf("Autocommit ist %s\n", $row[0]);
try {
/* Insert-Anweisung vorbereiten */
$stmt = mysqli_prepare($mysqli, 'INSERT INTO language(Code, Speakers) VALUES (?,?)');
mysqli_stmt_bind_param($stmt, 'ss', $language_code, $native_speakers);
/* Ein paar Werte einfügen */
$language_code = 'DE';
$native_speakers = 50_123_456;
mysqli_stmt_execute($stmt);
$language_code = 'FR';
$native_speakers = 40_546_321;
mysqli_stmt_execute($stmt);
/* Übertragung der Daten in die Datenbank. Dies setzt nicht autocommit=true */
mysqli_commit($mysqli);
print "2 Datensätze in die Datenbank übertragen\n";
$result = mysqli_query($mysqli, "SELECT @@autocommit");
$row = mysqli_fetch_row($result);
printf("Autocommit ist %s\n", $row[0]);
/* Versuchen, weitere Werte einzufügen */
$language_code = 'PL';
$native_speakers = 30_555_444;
mysqli_stmt_execute($stmt);
$language_code = 'DK';
$native_speakers = 5_222_444;
mysqli_stmt_execute($stmt);
/* Das Setzen von autocommit=true löst eine Übertragung aus */
mysqli_autocommit($mysqli, true);
print "2 weitere Datensätze in die Datenbank übertragen\n";
} catch (mysqli_sql_exception $exception) {
mysqli_rollback($mysqli);
throw $exception;
}
Die obigen Bespiele erzeugen folgende Ausgabe:
Autocommit ist 0 2 Datensätze in die Datenbank übertragen Autocommit ist 0 2 weitere Datensätze in die Datenbank übertragen Autocommit ist 0 2 Datensätze in die Datenbank übertragen Autocommit ist 0 2 weitere Datensätze in die Datenbank übertragen
Siehe auch
- mysqli_begin_transaction() - Starts a transaction
- mysqli_commit() - Commits the current transaction
- mysqli_rollback() - Rolls back current transaction
add a note
User Contributed Notes 4 notes
Geoffrey Thubron ¶
16 years ago
jcwebb at dicoe dot com ¶
16 years ago
Just to be clear, autocommit not only turns on/off transactions, but will also 'commit' any waiting queries.
<?php
mysqli_autocommit($link, FALSE); // turn OFF auto
-some query 1;
-some query 2;
mysqli_commit($link); // process ALL queries so far
-some query 3;
-some query 4;
mysqli_autocommit($link, TRUE); // turn ON auto
?>
All 4 will be processed.
Glen ¶
17 years ago
I've found that if PHP exits due to a code bug during a transaction, an InnoDB table can remain locked until Apache is restarted.
The simple test is to start a transaction by setting $mysqli_obj->autocommit(false) and executing an insert statement. Before getting to a $mysqli_obj->commit statement - have a runtime code bug bomb PHP. You check the database, no insert happened (you assume a rollback occurred) .. and you go fix the bug, and try again... but this time the script takes about 50 seconds to timeout - the insert statement returning with a “1205 - Lock wait timeout exceeded; try restarting transaction”. No rollback occurred. And this error will not go away until you restart Apache - for whatever reason, the resources are not released until the process is killed.
I found that an ‘exit’, instead of a PHP code bug, will not cause a problem. So there is an auto-rollback mechanism in place - it just fails miserably when PHP dies unexpectantly. Having to restarting apache is a pretty drastic measure to overcome a code bug.
To avoid this problem, I use “register_shutdown_function()” when I start a transaction, and set a flag to indicate a transaction is in process (because there is no unregister_shutdown_function()). See below. So the __shutdown_check() routine (I beleive it needs to be public) is called when the script bombs - which is able to invoke the rollback().
these are just the relevant bits to give u an idea...
<?php
public function begin_transaction() {
$ret = $this->mysqli_obj->autocommit(false);
$this->transaction_in_progress = true;
register_shutdown_function(array($this, "__shutdown_check"));
}
public function __shutdown_check() {
if ($this->transaction_in_progress) {
$this->rollback();
}
}
public function commit() {
$ret = $this->mysqli_obj->commit();
$this->transaction_in_progress = false;
}
public function rollback() {
$ret = $this->mysqli_obj->rollback();
$this->transaction_in_progress = false;
}
?>
True for PHP 5.1.6 + MySQL 5.0.24a.
will at phpfever dot com ¶
18 years ago
If you are using the mysql command line tool, here are some helpful hints for the autocommit feature:
1. To view the current autocommit setting, you can use this query: select @@autocommit; It will return the current setting as 1 or 0 (on or off)
2. You can manage the default autocommit feature in you my.cnf or my.ini by adding the following line: init_connect='set autocommit=0'. I'm pretty sure this isn't in the documentation, but it does work.
Here are the current engines, as of MySQL 5.1dev that support transactions:
InnoDB
BerkeleyDB
Falcon
Falcon is very new, so beware using it on production systems.
