那些遇到过的问题

PHP PDO MySQL以及它如何真正处理MySQL事务？

ton*_*nix 5 php mysql pdo locking transactions

我试图克服它,但我无法理解使用PDO和MySQL在PHP中进行事务处理的逻辑.

我知道这个问题会很长,但我认为这是值得的.

鉴于我阅读了很多关于MySQL事务的信息,服务器如何处理它们,它们与锁和其他隐式提交语句的关系等等,不仅在SO上,而且在MySQL和PHP手册上:

并给出此代码:

模式:

CREATE TABLE table_name (
  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
  table_col VARCHAR(100) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

CREATE TABLE `another_table` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `another_col` varchar(100) COLLATE utf8_unicode_ci DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
Run Code Online (Sandbox Code Playgroud)

test1.php(with PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)):

<?php

// PDO
define('DB_HOST', 'localhost');
define('DB_USER', 'user');
define('DB_PASS', 'password');
define('DB_NAME', 'db_name');

/**
 * Uses `$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);`
 */
class Database {

    private $host = DB_HOST;
    private $user = DB_USER;
    private $pass = DB_PASS;
    private $dbname = DB_NAME;

    private $pdo;

    public $error;

    private $stmt;


    public function __construct($host=NULL,$user=NULL,$pass=NULL,$dbname=NULL) {

        if ($host!==NULL)
            $this->host=$host;

        if ($user!==NULL)
            $this->user=$user;

        if ($pass!==NULL)
            $this->pass=$pass;

        if ($dbname!==NULL)
            $this->dbname=$dbname;

        // Set DSN
        $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;

        // Set options
        $options = array(
            PDO::ATTR_PERSISTENT    => false,
            PDO::ATTR_ERRMODE       => PDO::ERRMODE_EXCEPTION
        );

        // Create a new PDO instanace
        $this->pdo = new PDO($dsn, $this->user, $this->pass, $options);
        $this->pdo->exec("SET NAMES 'utf8'");

    }

    public function cursorClose() {
        $this->stmt->closeCursor();
    }

    public function close() {
        $this->pdo = null;
        $this->stmt = null;
        return true;
    }

    public function beginTransaction() {
        $this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);
        return $this->pdo->beginTransaction();
    }

    public function commit() {
        $ok = $this->pdo->commit();
        $this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    }

    public function rollback() {
        $ok = $this->pdo->rollback();
        $this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    }

    public function bind($param, $value, $type = null){
        if (is_null($type)) {
            switch (true) {
                case is_int($value):
                    $type = PDO::PARAM_INT;
                    break;
                case is_bool($value):
                    $type = PDO::PARAM_BOOL;
                    break;
                case is_null($value):
                    $type = PDO::PARAM_NULL;
                    break;
                default:
                    $type = PDO::PARAM_STR;
            }
        }
        $this->stmt->bindValue($param, $value, $type);
    }

    public function runquery() {
        $this->stmt->execute();
    }

    public function execute($nameValuePairArray = NULL) {
        try {   
            if (is_array($nameValuePairArray) && !empty($nameValuePairArray)) 
                return $this->stmt->execute($nameValuePairArray);
            else
                return $this->stmt->execute();
        } 
        catch(PDOException $e) {
            $this->error = $e->getMessage();
        }   
        return FALSE;
    }

    public function lastInsertId() {
        return $this->pdo->lastInsertId();
    }

    public function insert($table, $data) {

        if (!empty($data)){

            $fields = "";

            $values = "";

            foreach($data as $field => $value) {

                if ($fields==""){
                    $fields = "$field";
                    $values = ":$field";
                }
                else {
                    $fields .= ",$field";
                    $values .= ",:$field";
                }
            }

            $query = "INSERT INTO $table ($fields) VALUES ($values) ";

            $this->query($query);

            foreach($data as $field => $value){
                $this->bind(":$field",$value);
            }

            if ($this->execute()===FALSE)
                return FALSE;
            else
                return $this->lastInsertId();   
        }

        $this->error = "No fields during insert";

        return FALSE;
    }

    public function query($query) {
        $this->stmt = $this->pdo->prepare($query);
    }

    public function setBuffered($isBuffered=false){
        $this->pdo->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, $isBuffered);
    }

    public function lockTables($tables){
        $query = "LOCK TABLES ";
        foreach($tables as $table=>$lockType){
            $query .= "{$table} {$lockType}, ";
        }
        $query = substr($query,0, strlen($query)-2);
        $this->query($query);
        return $this->execute();
    }

    public function unlockTables(){
        $query = "UNLOCK TABLES";
        $this->query($query);
        return $this->execute();
    }
}

$db = NULL;
try {
    $db = new Database();
    $db->beginTransaction();

    // If I call `LOCK TABLES` here... No implicit commit. Why?
    // Does `$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);` prevent it?
    $db->lockTables(array('another_table' => 'WRITE'));

    $db->insert('another_table', array('another_col' => 'TEST1_ANOTHER_TABLE'));

    $db->unlockTables();


    // If I insert a row, other MySQL clients do not see it. Why?
    // I called `LOCK TABLES` above and as the MySQL manual says:
    // 
    //      LOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.
    //
    $db->insert('table_name', array('table_col' => 'TEST1_TABLE_NAME'));

    //...
    // If I rollback for some reason, everything rolls back, but shouldn't the transaction
    // be already committed with the initial `LOCK TABLES`?
    // So I should expect to get a PDOException like "There's no active transaction" or something similar, shouldn't I?
    //$db->rollback();

    // If I commit instead of the above `$db->rollback()` line, everything is committed, but only now other clients see the new row in `table_name`,
    // not straightforward as soon I called `$db->insert()`, whereas I guess they should have seen the change
    // even before the following line because I am using `LOCK TABLES` before (see `test2.php`).
    $db->commit();
}
catch (PDOException $e) {
    echo $e->getMessage();
}

if (!is_null($db)) {
    $db->close();
}
Run Code Online (Sandbox Code Playgroud)

test2.php(没有PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)行的数据库(注释掉)):

<?php

// PDO
define('DB_HOST', 'localhost');
define('DB_USER', 'user');
define('DB_PASS', 'password');
define('DB_NAME', 'db_name');

/**
 * Does not use `$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);`
 */
class Database {

    private $host = DB_HOST;
    private $user = DB_USER;
    private $pass = DB_PASS;
    private $dbname = DB_NAME;

    private $pdo;

    public $error;

    private $stmt;


    public function __construct($host=NULL,$user=NULL,$pass=NULL,$dbname=NULL) {

        if ($host!==NULL)
            $this->host=$host;

        if ($user!==NULL)
            $this->user=$user;

        if ($pass!==NULL)
            $this->pass=$pass;

        if ($dbname!==NULL)
            $this->dbname=$dbname;

        // Set DSN
        $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;

        // Set options
        $options = array(
            PDO::ATTR_PERSISTENT    => false,
            PDO::ATTR_ERRMODE       => PDO::ERRMODE_EXCEPTION
        );

        // Create a new PDO instanace
        $this->pdo = new PDO($dsn, $this->user, $this->pass, $options);
        $this->pdo->exec("SET NAMES 'utf8'");

    }

    public function cursorClose() {
        $this->stmt->closeCursor();
    }

    public function close() {
        $this->pdo = null;
        $this->stmt = null;
        return true;
    }

    public function beginTransaction() {
        //$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,0);
        return $this->pdo->beginTransaction();
    }

    public function commit() {
        $ok = $this->pdo->commit();
        //$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    }

    public function rollback() {
        $ok = $this->pdo->rollback();
        //$this->pdo->setAttribute(PDO::ATTR_AUTOCOMMIT,1);
        return $ok;
    }

    public function bind($param, $value, $type = null){
        if (is_null($type)) {
            switch (true) {
                case is_int($value):
                    $type = PDO::PARAM_INT;
                    break;
                case is_bool($value):
                    $type = PDO::PARAM_BOOL;
                    break;
                case is_null($value):
                    $type = PDO::PARAM_NULL;
                    break;
                default:
                    $type = PDO::PARAM_STR;
            }
        }
        $this->stmt->bindValue($param, $value, $type);
    }

    public function runquery() {
        $this->stmt->execute();
    }

    public function execute($nameValuePairArray = NULL) {
        try {   
            if (is_array($nameValuePairArray) && !empty($nameValuePairArray)) 
                return $this->stmt->execute($nameValuePairArray);
            else
                return $this->stmt->execute();
        } 
        catch(PDOException $e) {
            $this->error = $e->getMessage();
        }   
        return FALSE;
    }

    public function lastInsertId() {
        return $this->pdo->lastInsertId();
    }

    public function insert($table, $data) {

        if (!empty($data)){

            $fields = "";

            $values = "";

            foreach($data as $field => $value) {

                if ($fields==""){
                    $fields = "$field";
                    $values = ":$field";
                }
                else {
                    $fields .= ",$field";
                    $values .= ",:$field";
                }
            }

            $query = "INSERT INTO $table ($fields) VALUES ($values) ";

            $this->query($query);

            foreach($data as $field => $value){
                $this->bind(":$field",$value);
            }

            if ($this->execute()===FALSE)
                return FALSE;
            else
                return $this->lastInsertId();   
        }

        $this->error = "No fields during insert";

        return FALSE;
    }

    public function query($query) {
        $this->stmt = $this->pdo->prepare($query);
    }

    public function setBuffered($isBuffered=false){
        $this->pdo->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, $isBuffered);
    }

    public function lockTables($tables){
        $query = "LOCK TABLES ";
        foreach($tables as $table=>$lockType){
            $query .= "{$table} {$lockType}, ";
        }
        $query = substr($query,0, strlen($query)-2);
        $this->query($query);
        return $this->execute();
    }

    public function unlockTables(){
        $query = "UNLOCK TABLES";
        $this->query($query);
        return $this->execute();
    }
}

$db = NULL;
try {
    $db = new Database();
    $db->beginTransaction();

    // If I call `LOCK TABLES` here... There's an implicit commit.
    $db->lockTables(array('another_table' => 'WRITE'));

    $db->insert('another_table', array('another_col' => 'TEST2_ANOTHER_TABLE'));

    $db->unlockTables();


    // If I insert a row, other MySQL clients see it straightforward (no need to reach `$db->commit()`).
    // This is coherent with the MySQL manual:
    // 
    //      LOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.
    //
    $db->insert('table_name', array('table_col' => 'TEST2_TABLE_NAME'));

    //...
    // If I rollback for some reason, the row does not rollback, as the transaction
    // was already committed with the initial `LOCK TABLES` statement above.
    // 
    // I cannot rollback the insert into table `table_name`
    // 
    // So I should expect to get a PDOException like "There's no active transaction" or something similar, shouldn't I?
    $db->rollback();

    // If I commit instead of the above `$db->rollback()` line, I guess nothing happens, because the transaction
    // was already committed and as I said above, and clients already saw the changes before this line was reached.
    // Again, this is coherent with the MySQL statement:
    //
    //       LOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.
    //
    //$db->commit();
}
catch (PDOException $e) {
    echo $e->getMessage();
}

if (!is_null($db)) {
    $db->close();
}
Run Code Online (Sandbox Code Playgroud)

我仍然有以下疑问和未回答的问题:

  • 使用InnoDB,有没有之间的差异 PDO::beginTransaction(),并PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)当我们使用PDO与普通的MySQL的语句在MySQL和PHP /或SET AUTOCOMMIT = 0;与START TRANSACTION;？如果是,那是什么？

    如果你检查我的PHP示例,在Database::beginTransaction()包装器方法中我使用PDO::beginTransaction()和PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)文件test1.php中的两个并且不要PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)在文件test2.php中使用.我发现当我使用时会发生奇怪的事情PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0):

    • 使用PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)line in Database(test1.php),在带有LOCK TABLES语句的事务中,LOCK TABLES 似乎没有隐式提交事务,因为如果我连接另一个客户端,我看不到插入的$db->commit();行,直到代码到达行,而MySQL手册说:

      LOCK TABLES不是事务安全的,并且在尝试锁定表之前隐式提交任何活动事务.

      因此,我们可以说PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)(在MySQL上会是这样的 SET AUTOCOMMIT = 0;)一个事务不是由像这样的语句隐式提交的LOCK TABLES吗？然后我会说MySQL手册和PHP PDO实现之间存在不一致(我不是在抱怨,我只想了解);

    • 如果没有(test2.php)中的PDO::setAttribute(PDO::ATTR_AUTOCOMMIT, 0)行,代码似乎与MySQL的手册一致:一旦到达查询,就会有一个隐式提交,所以在行之后其他客户端甚至可以在到达之前看到新插入的行;DatabaseLOCK TABLES is not transaction-safe and implicitly commits any active transaction before attempting to lock the tables.LOCK TABLES$db->insert('table_name', array('table_col' => 'TEST2_TABLE_NAME'));$db->commit();

我刚刚描述的以下行为的解释是什么？当我们使用PHP PDO并implicit-commit在事务中包含语句时,事务如何工作？

我的PHP版本是7.0.22,MySQL版本是5.7.20.

感谢您的关注.

Bil*_*win 1

https://dev.mysql.com/doc/refman/5.7/en/innodb-autocommit-commit-rollback.html says:

If autocommit mode is disabled within a session with SET autocommit = 0, the session always has a transaction open. A COMMIT or ROLLBACK statement ends the current transaction and a new one starts.

So when you set autocommit=0 in a session (call it session 1), this implicitly opens a transaction, and leaves it open indefinitely.

The default transaction isolation level is REPEATABLE-READ. So your session will not see a refreshed view of committed changes from other sessions' work until session 1 explicitly commits or rolls back.

另一个会话 2 中的 LOCK TABLES确实会导致隐式提交，但会话 1 看不到结果，因为由于其自己的事务快照，它仍然只能看到数据的隔离视图。

归档时间：

查看次数：

556 次

最近记录：

7 年，9 月 前
SET autocommit = 1和mysql中的START TRANSACTION之间的区别(我错过了什么？) 67
事务内的Mysql事务 50
PDO,mysql,事务和表锁定 15
更多相关链接
相关归档
"Mysql行大小太大"的更改限制 91
MySQL Workbench不显示查询结果 70
我可以在xdebug profiler上手动说出在特定位置开始分析吗？ 33
按字段的月份选择 19
切换vs if语句 19
以md5格式将密码插入数据库？ 12
找不到也不能安装mysql_config 12
SQL Server和事务中间的连接丢失 11
MySQL:在select本身中使用select中的值 10
使用PDO语法错误或访问冲突 2
难疑归档
C++中的" - >"运算符是什么？ 8590
如何从JavaScript中删除数组中的特定元素？ 7655
从Git中的分支中删除提交 3035
在JavaScript中验证十进制数 - IsNumeric() 2318
如何使用对象作为成员循环一个普通的JavaScript对象？ 1521
在文本框中的Enter键上使用JavaScript触发按钮单击 1250
如何完全卸载Node.js,并从头开始重新安装(Mac OS X) 1196
在HTML中嵌入PDF的推荐方法？ 1128
什么是"Linting"？ 1044
用于Python的IDE是什么？ 1028