PHP implements volume backup of mysql database

<?php
//宋正河 转载请注明出处
set_time_limit(0);
header(&#39;content-type:text/html;charset=utf-8&#39;);
mysql_connect(&#39;localhost&#39;,&#39;root&#39;,&#39;root&#39;);
mysql_select_db(&#39;test&#39;);
$table_array=get_tables(&#39;test&#39;);
mysql_query(&#39;set names utf8&#39;);
$filesize=1024*1024*4;
$start=$_GET[&#39;start&#39;]?$_GET[&#39;start&#39;]:0;
$part=$_GET[&#39;part&#39;]?$_GET[&#39;part&#39;]:&#39;1&#39;;
$table_index=$_GET[&#39;table_index&#39;]?$_GET[&#39;table_index&#39;]:&#39;0&#39;;
$table=$table_array[$table_index];
$num=200000000;//这个数要足够大,可以是总记录数
$backupdata=&#39;&#39;;
if($start==&#39;0&#39;){
$query="SHOW CREATE TABLE `{$table}`";
$result = mysql_query($query);
$row = mysql_fetch_row($result);
$backupdata .= "DROP TABLE IF EXISTS `{$table}`;\n" . $row[1] . ";\n\n";
}
$limit=($start==&#39;0&#39;)?&#39;&#39;:" limit $start,$num ";
$query="select * from `{$table}` $limit ";
$result=mysql_query($query);
$numfields = mysql_num_fields($result); //统计字段数
while($row=mysql_fetch_row($result)){
$comma = &#39;&#39;; //存储逗号
$backupdata_tmp = "INSERT INTO `{$table}` VALUES (";
for($i=0; $i<$numfields; $i++){
$backupdata_tmp .= $comma . "&#39;" . mysql_escape_string($row[$i]) . "&#39;";
$comma = &#39;,&#39;;
}
$backupdata_tmp .= ");\n";
if(strlen($backupdata)+strlen($backupdata_tmp) > $filesize){
//写入文件并跳转
$file=&#39;data/&#39;.$table.&#39;-&#39;.$part.&#39;.sql&#39;;
file_put_contents($file,$backupdata);
echo $file.&#39; 备份完成，程序继续进行！&#39;;
$part++;
//分段
//表名
//起点
//跳转
sleep(3);
echo "<script>location.href=&#39;?start={$start}&table_index={$table_index}&part={$part}&#39;;</script>";
exit;
}
$backupdata.=$backupdata_tmp;
$start++;
}
if($backupdata){
$file=&#39;data/&#39;.$table.&#39;-&#39;.$part.&#39;.sql&#39;;
file_put_contents($file,$backupdata);
}
echo $table.&#39;备份完成！<br />&#39;;
sleep(2);
$table_index++;
if($table_array[$table_index]){
echo "<script>location.href=&#39;?table_index={$table_index}&#39;;</script>";
exit;
}else{
echo &#39;恭喜你，数据库备份完毕！&#39;;
}
function get_tables($db){
$tq = mysql_list_tables($db);
while($tr = mysql_fetch_row($tq)){
$arrtb[] = $tr[0];
}
return $arrtb;
}
?>