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mysqli::autocommit

mysqli_autocommit

(PHP 5)

mysqli::autocommit -- mysqli_autocommit — Turns on or off auto-commiting database modifications

说明

面向对象风格

bool mysqli::autocommit ( bool $mode )

过程化风格

bool mysqli_autocommit ( mysqli $link , bool $mode )

Turns on or off auto-commit mode on queries for the database connection.

To determine the current state of autocommit use the SQL command SELECT @@autocommit.

参数

link

仅以过程化样式：由 mysqli_connect() 或 mysqli_init() 返回的链接标识。

mode

Whether to turn on auto-commit or not.

返回值

成功时返回 TRUE， 或者在失败时返回 FALSE.

注释

Note:

This function doesn't work with non transactional table types (like MyISAM or ISAM).

范例

Example #1 mysqli::autocommit() example

面向对象风格

<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}

/* turn autocommit on */
$mysqli->autocommit(TRUE);

if ($result = $mysqli->query("SELECT @@autocommit")) {
    $row = $result->fetch_row();
    printf("Autocommit is %s\n", $row[0]);
    $result->free();
}

/* close connection */
$mysqli->close();
?>

过程化风格

<?php
$link = mysqli_connect("localhost", "my_user", "my_password", "world");

if (!$link) {
    printf("Can't connect to localhost. Error: %s\n", mysqli_connect_error());
    exit();
}

/* turn autocommit on */
mysqli_autocommit($link, TRUE);

if ($result = mysqli_query($link, "SELECT @@autocommit")) {
    $row = mysqli_fetch_row($result);
    printf("Autocommit is %s\n", $row[0]);
    mysqli_free_result($result);
}

/* close connection */
mysqli_close($link);
?>

以上例程会输出：

Autocommit is 1

参见

MySQLi
在线手册：中文 英文
PHP手册
PHP手册 - N: Turns on or off auto-commiting database modifications

用户评论:

jcwebb at dicoe dot com (11-Nov-2007 09:03)

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.

Geoffrey Thubron (13-May-2007 02:02)

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.

Glen (11-Mar-2007 08:22)

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 (27-Apr-2006 09:22)

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.