PDO MYSQL_ATTR_USE_BUFFERED_QUERY 不生效

Question

我有以下粗略的代码（完整代码146行，其中90行是字符串解析，如果需要可以添加）：

ini_set('memory_limit', '7G');
$db = new PDO("mysql:host=".$dbhost.";dbname=".$dbname, $dbuser, $dbpass, array(PDO::ATTR_PERSISTENT => true));
$db->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, false);
$db_ub = new PDO("mysql:host=".$dbhost.";dbname=".$dbname, $dbuser, $dbpass, array(PDO::ATTR_PERSISTENT => true));
$db_ub->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true);
$stmt = $db->prepare('select columns from stats where timestamp between ? and ?');
$stmt->execute(array('2020-04-25', '2020-05-25'));
while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
      echo memory_get_usage() .PHP_EOL;
      echo $row['id'] . PHP_EOL;
      $stmt2 = $db_ub->prepare('select somedata from users limit 1');
      $stmt2->execute();
      $row2 = $stmt2->fetch(PDO::FETCH_ASSOC);
      $type = !empty($row2['somedate']) ? 5 : 4;
      $result = $db_ub->prepare('insert ignore into newtable (old, type) values (?, ?)');
      $result->execute(array($row['id'], $type));
}

在$stmt->execute(array('2020-04-25', '2020-05-25'));我的内存消耗期间.34GB（ps aux | grep 'php ' | awk '{$5=int(100 * $5/1024/1024)/100"GB";}{ print;}'用于监控消耗期间select和show full processlistSQL 端验证）。一旦脚本进入，while它就会跳转到 +5 GB。

测试 setattribute

var_dump($db->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, false));

好像已经生效了：

bool(true)

但是当我切换缓冲或无缓冲时，行为不会改变。

$db->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, false)

和

$db->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true)

使用echo $db->getAttribute(constant('PDO::MYSQL_ATTR_USE_BUFFERED_QUERY'));还显示设置更改。

将设置移动到语句而不是连接作为https://www.php.net/manual/en/ref.pdo-mysql.php建议也没有工作。

$stmt = $db->prepare('select columns from stats where timestamp between ? and ?', array(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => false));

我还尝试将缓冲区设置移动到连接而没有任何影响：

$db = new PDO("mysql:host=".$dbhost.";dbname=".$dbname, $dbuser, $dbpass, array(PDO::ATTR_PERSISTENT => true, PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => false));

取出第二个连接似乎允许无缓冲查询按预期运行：

ini_set('memory_limit', '1G');
$db = new PDO("mysql:host=".$dbhost.";dbname=".$dbname, $dbuser, $dbpass, array(PDO::ATTR_PERSISTENT => true, PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => false));
$db->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, false);
//$db_ub = new PDO("mysql:host=".$dbhost.";dbname=".$dbname, $dbuser, $dbpass, array(PDO::ATTR_PERSISTENT => true));
//$db_ub->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true);
$stmt = $db->prepare('select columns from stats where timestamp between ? and ?');
$stmt->execute(array('2019-01-25', '2019-11-25'));
while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
      echo memory_get_usage() .PHP_EOL;
      echo $row['id'] . PHP_EOL;
      /*
     $stmt2 = $db_ub->prepare('select somedata from users limit 1');
      $stmt2->execute();
      $row2 = $stmt2->fetch(PDO::FETCH_ASSOC);
      $type = !empty($row2['somedate']) ? 5 : 4;
      $result = $db_ub->prepare('insert ignore into newtable (old, type) values (?, ?)');
      $result->execute(array($row['id'], $type));
     */
}

这种用法memory_get_usage不超过379999.

如果我取消注释第二个连接并使其无缓冲，我会收到：

Cannot execute queries while other unbuffered queries are active.  Consider using PDOStatement::fetchAll().  Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute.

缓冲的第二个连接如最初描述的那样执行，执行时消耗大量内存。如果ini_set('memory_limit'高它工作如果低它错误。使用大memory_limit的不是一个可行的解决方案。

正在使用 ( Red Hat Enterprise Linux Server release 7.3 (Maipo)):

php71u-pdo.x86_64                  7.1.19-1.ius.centos7

将脚本移至较新的机器 ( Amazon Linux release 2 (Karoo))：

php73-pdo.x86_64                   7.3.17-1.el7.ius

并有相同的行为。

Answer 1

该PDO::ATTR_PERSISTENT值不是布尔值。它标识正在使用的连接，对多个连接使用唯一值。就我而言：

$db = new PDO("mysql:host=".$dbhost.";dbname=".$dbname, $dbuser, $dbpass, array(PDO::ATTR_PERSISTENT => 'unbuff', PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => false));
$db_ub = new PDO("mysql:host=".$dbhost.";dbname=".$dbname, $dbuser, $dbpass, array(PDO::ATTR_PERSISTENT => 'buff', PDO::MYSQL_ATTR_USE_BUFFERED_QUERY => true));