MySQL server has gone away問題解決方法

may0505

　1、應(yīng)用程序（比如PHP）長時間的執(zhí)行批量的MYSQL語句。最常見的就是采集或者新舊數(shù)據(jù)轉(zhuǎn)化。

　　解決方案：

　　在my.cnf文件中添加或者修改以下兩個變量：

wait_timeout=2880000
interactive_timeout = 2880000　　
關(guān)于兩個變量的具體說明可以google或者看官方手冊。如果不能修改my.cnf，則可以在連接數(shù)據(jù)庫的時候設(shè)置CLIENT_INTERACTIVE，比如：

sql = "set interactive_timeout=24*3600";
mysql_real_query(...)

　　2、執(zhí)行一個SQL，但SQL語句過大或者語句中含有BLOB或者longblob字段。比如，圖片數(shù)據(jù)的處理

　　解決方案：

　　在my.cnf文件中添加或者修改以下變量：

max_allowed_packet = 10M
(也可以設(shè)置自己需要的大小)

max_allowed_packet
參數(shù)的作用是，用來控制其通信緩沖區(qū)的最大長度

MySQL: 詭異的MySQL server has gone away及其解決
來自：http://fz9493.blog.sohu.com/38472203.html

jimmy | 15 三月, 2007 20:32

在Mysql執(zhí)行show status，通常更關(guān)注緩存效果、進程數(shù)等，往往忽略了兩個值：

Variable_name Value
Aborted_clients 3792
Aborted_connects 376


通常只占query的0.0x%，所以并不為人所**。而且在傳統(tǒng)Web應(yīng)用上，query錯誤對用戶而言影響并不大，只是重新刷新一下頁面就OK了。最近的基礎(chǔ)改造中，把很多應(yīng)用作為service運行，無法提示用戶重新刷新，這種情況下，可能就會影響到服務(wù)的品質(zhì)。

通過程序腳本的日志跟蹤，主要報錯信息為“MySQL server has gone away”。官方的解釋是：

The most common reason for the MySQL server has gone away error is that the server timed out and closed the connection.

Some other common reasons for the MySQL server has gone away error are:

You (or the db administrator) has killed the running thread with a KILL statement or a mysqladmin kill command.

You tried to run a query after closing the connection to the server. This indicates a logic error in the application that should be corrected.

A client application running on a different host does not have the necessary privileges to connect to the MySQL server from that host.

You got a timeout from the TCP/IP connection on the client side. This may happen if you have been using the commands: mysql_options(..., MYSQL_OPT_READ_TIMEOUT,...) or mysql_options(..., MYSQL_OPT_WRITE_TIMEOUT,...). In this case increasing the timeout may help solve the problem.

You have encountered a timeout on the server side and the automatic reconnection in the client is disabled (the reconnect flag in the MYSQL structure is equal to 0).

You are using a Windows client and the server had dropped the connection (probably because wait_timeout expired) before the command was issued.

The problem on Windows is that in some cases MySQL doesn't get an error from the OS when writing to the TCP/IP connection to the server, but instead gets the error when trying to read the answer from the connection.

In this case, even if the reconnect flag in the MYSQL structure is equal to 1, MySQL does not automatically reconnect and re-issue the query as it doesn't know if the server did get the original query or not.

The solution to this is to either do a mysql_ping on the connection if there has been a long time since the last query (this is what MyODBC does) or set wait_timeout on the mysqld server so high that it in practice never times out.

You can also get these errors if you send a query to the server that is incorrect or too large. If mysqld receives a packet that is too large or out of order, it assumes that something has gone wrong with the client and closes the connection. If you need big queries (for example, if you are working with big BLOB columns), you can increase the query limit by setting the server's max_allowed_packet variable, which has a default value of 1MB. You may also need to increase the maximum packet size on the client end. More information on setting the packet size is given in Section A.1.2.9, “Packet too large”.

An INSERT or REPLACE statement that inserts a great many rows can also cause these sorts of errors. Either one of these statements sends a single request to the server irrespective of the number of rows to be inserted; thus, you can often avoid the error by reducing the number of rows sent per INSERT or REPLACE.

You also get a lost connection if you are sending a packet 16MB or larger if your client is older than 4.0.8 and your server is 4.0.8 and above, or the other way around.

It is also possible to see this error if hostname lookups fail (for example, if the DNS server on which your server or network relies goes down). This is because MySQL is dependent on the host system for name resolution, but has no way of knowing whether it is working — from MySQL's point of view the problem is indistinguishable from any other network timeout.

You may also see the MySQL server has gone away error if MySQL is started with the --skip-networking option.

Another networking issue that can cause this error occurs if the MySQL port (default 3306) is blocked by your firewall, thus preventing any connections at all to the MySQL server.

You can also encounter this error with applications that fork child processes, all of which try to use the same connection to the MySQL server. This can be avoided by using a separate connection for each child process.

You have encountered a bug where the server died while executing the query.


據(jù)此分析，可能原因有3：

1，Mysql服務(wù)端與客戶端版本不匹配。

2，Mysql服務(wù)端配置有缺陷或者優(yōu)化不足

3，需要改進程序腳本

通過更換多個服務(wù)端與客戶端版本，發(fā)現(xiàn)只能部分減少報錯，并不能完全解決。排除1。

對服務(wù)端進行了徹底的優(yōu)化，也未能達到理想效果。在timeout的取值設(shè)置上，從經(jīng)驗值的10，到PHP默認(rèn)的60，進行了多次嘗試。而Mysql官方默認(rèn)值(8小時)明顯是不可能的。從而對2也進行了排除。(更多優(yōu)化的經(jīng)驗分享，將在以后整理提供)

針對3對程序代碼進行分析，發(fā)現(xiàn)程序中大量應(yīng)用了類似如下的代碼(為便于理解，用原始api描述)：

$conn=mysql_connect( ... ... );

... ... ... ...

if(!$conn){ //reconnect

$conn=mysql_connect( ... ... );

}

mysql_query($sql, $conn);

這段代碼的含義，與Mysql官方建議的方法思路相符[ If you have a script, you just have to issue the query again for the client to do an automatic reconnection. ]。在實際分析中發(fā)現(xiàn)，if(!$conn)并不是可靠的，程序通過了if(!$conn)的檢驗后，仍然會返回上述錯誤。

對程序進行了改寫：

if(!conn){ // connect ...}

elseif(!mysql_ping($conn)){ // reconnect ... }

mysql_query($sql, $conn);

經(jīng)實際觀測，MySQL server has gone away的報錯基本解決。

BTW： 附帶一個關(guān)于 reconnect 的疑問，

在php4x+client3x+mysql4x的舊環(huán)境下，reconnet的代碼：

$conn=mysql_connect(...) 可以正常工作。

但是，在php5x+client4x+mysql4x的新環(huán)境下，$conn=mysql_connect(...)返回的$conn有部分情況下不可用。需要書寫為：

mysql_close($conn);

$conn=mysql_connect(...);

返回的$conn才可以正常使用。原因未明。未做深入研究，也未見相關(guān)討論�；蛟Smysql官方的BUG匯報中會有吧。

～～呵呵～～


本文來自CSDN博客，轉(zhuǎn)載請標(biāo)明出處：http://blog.csdn.net/brightsnow/archive/2009/03/17/3997705.aspx


description:
remember that your MySQL "max_allowed_packet" configuration setting (default 1MB)
mysql 默認(rèn)最大能夠處理的是1MB
如果你在sql使用了大的text或者BLOB數(shù)據(jù)，就會出現(xiàn)這個問題。 php手冊上的注釋

When trying to INSERT or UPDATE and trying to put a large amount of text or data (blob) into a mysql table you might run into problems.
In mysql.err you might see:
Packet too large (73904)
To fix you just have to start up mysql with the option -O max_allowed_packet=maxsize
You would just replace maxsize with the max size you want to insert, the default is 65536


mysql手冊上說

Both the client and the server have their own max_allowed_packet variable, so if you want to handle big packets, you must increase this variable both in the client and in the server.

If you are using the mysql client program, its default max_allowed_packet variable is 16MB. To set a larger value, start mysql like this:

shell> mysql --max_allowed_packet=32M That sets the packet size to 32MB.

The server's default max_allowed_packet value is 1MB. You can increase this if the server needs to handle big queries (for example, if you are working with big BLOB columns). For example, to set the variable to 16MB, start the server like this:

shell> mysqld --max_allowed_packet=16M You can also use an option file to set max_allowed_packet. For example, to set the size for the server to 16MB, add the following lines in an option file:

[mysqld]max_allowed_packet=16M

使用mysql做數(shù)據(jù)庫還原的時候，由于有些數(shù)據(jù)很大，會出現(xiàn)這樣的錯誤：The MySQL Server returned this Error:MySQL Error Nr.2006-MySQL server has gone away。我的一個150mb的備份還原的時候就出現(xiàn)了這錯誤。解決的方法就是找到mysql安裝目錄，找到my.ini文件，在文件的最后添 加：max_allowed_packet = 10M(也可以設(shè)置自己需要的大小)。 max_allowed_packet 參數(shù)的作用是，用來控制其通信緩沖區(qū)的最大長度。