「PHP致命錯誤：允許的內存大小134217728字節耗盡」，同時生成數據庫備份

Question

我得到的主題。當我嘗試在文本文件中備份我的數據庫時。

function backup_tables($backup_filename, $tables = '*') 
{ 
    $conf = new JConfig(); 
    $dbhost = $conf->host; 
    $dbuser = $conf->user; 
    $dbpassword = $conf->password; 
    $dbname = $conf->db; 
    $link = mysql_connect($dbhost, $dbuser, $dbpassword); 
    mysql_select_db($dbname, $link) or die(mysql_error()); 
    $return = "drop database if exists `$dbname`;\n\ncreate database `$dbname`;\n\nuse `$dbname`;\n\n"; 
    $return .= "/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;\n\n"; 
    $return .= "/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;\n\n"; 
    $return .= "/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;\n\n"; 
    $return .= "/*!40101 SET NAMES utf8 */;\n\n"; 

    $handle = fopen($backup_filename, 'w+'); 
    fwrite($handle, $return); $return = ""; 

    // get all of the tables 
    if ($tables == '*') { 
     $tables = array(); 
     $result = mysql_query('SHOW TABLES'); 
     while ($row = mysql_fetch_row($result)) { 
      $tables[] = $row[0]; 
     } 
    } else { 
     $tables = is_array($tables) ? $tables : explode(',', $tables); 
    } 

    // cycle through 
    foreach ($tables as $table) { 
     $result = mysql_query('SELECT * FROM ' . $table); 
     $num_fields = mysql_num_fields($result); 
     $return .= 'DROP TABLE IF EXISTS `' . $table . '`;'; 
     $return .= "\n\n" . mysql_fetch_row(mysql_query('SHOW CREATE TABLE `' . $table . '`;'))[1] . " DEFAULT CHARSET=cp1251;\n\n"; 

     while ($row = mysql_fetch_row($result)) { 
      $return .= 'INSERT INTO ' . $table . ' VALUES('; 
      for ($i = 0; $i < $num_fields; $i++) { 
       $row[$i] = str_replace("\n", "\\n", addslashes($row[$i])); 
       $return .= '"' . (isset($row[$i])? $row[$i] : '') . '"'; 
       if ($num_fields - $i - 1) { 
        $return .= ','; 
       } 
      } 
      $return .= ");\n"; 

      fwrite($handle, $return); $return = ""; 
     } 
     if($return) { 
      fwrite($handle, $return); 
      $return .= "\n\n\n"; 
     } 
    } 

    fclose($handle); 
} 

這個函數可以很好的處理內存泄漏的異常。它創建一個〜30 MiB的文件，並提及提及的錯誤。正在進行文件生成時，httpd進程的內存使用量會一致增加。還有一件事：在一張大桌子（包含一個日誌）上生成一代，但我認爲這不是因爲逐行寫入的原因信息。

Answer 1

And one more: generation hungs at a large table (containing a log), but I think this is no matter 'cause information written row by row.

其實這是原因：我應該使用mysql_unbuffered_query代替mysql_query。現在這個功能看起來像這樣：

function backup_tables($backup_filename, $tables = '*') 
{ 
    $conf = new JConfig(); 
    $dbhost = $conf->host; 
    $dbuser = $conf->user; 
    $dbpassword = $conf->password; 
    $dbname = $conf->db; 
    $link = mysql_connect($dbhost, $dbuser, $dbpassword); 
    mysql_select_db($dbname, $link) or die(mysql_error()); 
    $return = "drop database if exists `$dbname`;\n\ncreate database `$dbname`;\n\nuse `$dbname`;\n\n"; 
    $return .= "/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;\n\n"; 
    $return .= "/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;\n\n"; 
    $return .= "/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;\n\n"; 
    $return .= "/*!40101 SET NAMES utf8 */;\n\n"; 

    $handle = fopen($backup_filename, 'w+'); 
    fwrite($handle, $return); $return = ""; 

    // get all of the tables 
    if ($tables == '*') { 
     $tables = array(); 
     $result = mysql_query("SHOW TABLES"); 
     while ($row = mysql_fetch_row($result)) { 
      $tables[] = $row[0]; 
     } 
    } else { 
     $tables = is_array($tables) ? $tables : explode(',', $tables); 
    } 

    // cycle through 
    foreach ($tables as $table) { 
     $return .= "DROP TABLE IF EXISTS `$table`;"; 
     $return .= "\n\n" . mysql_fetch_row(mysql_query("SHOW CREATE TABLE `$table`;"))[1] . " DEFAULT CHARSET=cp1251;\n\n"; 

     $result = mysql_unbuffered_query("SELECT * FROM `$table`"); 
     $num_fields = mysql_num_fields($result); 

     while ($row = mysql_fetch_row($result)) { 
      $return .= "INSERT INTO `$table` VALUES("; 
      for ($i = 0; $i < $num_fields; $i++) { 
       $row[$i] = str_replace("\n", "\\n", addslashes($row[$i])); 
       $return .= '"' . (isset($row[$i])? $row[$i] : '') . '"'; 
       if ($num_fields - $i - 1) { 
        $return .= ','; 
       } 
      } 
      $return .= ");\n"; 

      fwrite($handle, $return); $return = ""; 
     } 
     if($return) 
      fwrite($handle, $return); 

     $return = "\n\n\n"; 
    } 

    fclose($handle); 
} 

Answer 2

這裏的PHP答案是增加最大內存大小，如果不是最大執行時間在同一時間。

這是在重新創建mysqldump命令的練習之外，是否有理由在PHP代碼中執行此操作？

使用mysqldump或類似Holland http://hollandbackup.org/的東西可能會更好，可以逐個轉儲每個表。

Answer 3

當前答案使用deprecated function。新方法是使用mysqli::use_result。

在我的情況下，我跑進了耗盡的內存錯誤試圖寫入一個大的sql表到一個文件。以下是我使用它的方式。

$conn = new mysqli("localhost", "my_user", "my_password", "my_db"); 

$sql = 'SELECT row1, row2 from table'; 

$fp = fopen('output.json', 'w'); 
if ($conn->multi_query($sql)) { 
    do { 
     if ($result = $conn->use_result()) { 
      while ($row = $result->fetch_row()) { 
       $row1 = $row[0]; 
       $row2 = $row[1]; 
       $item = array('row1'=>$row1, 'row2'=>$row2); 
       fwrite($fp, json_encode($item)); 
      } 
      $result->close(); 
     } 
    } while ($conn->more_results() && $conn->next_result()); 
} 

fclose($fp); 
$conn->close();