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B.5.2.8 MySQL server has gone away

This section also covers the related Lost connection to server during query error.

The most common reason for the MySQL server has gone away error is that the server timed out and closed the connection. In this case, you normally get one of the following error codes (which one you get is operating system-dependent).

Error Code Description
CR_SERVER_GONE_ERROR The client couldn't send a question to the server.
CR_SERVER_LOST The client didn't get an error when writing to the server, but it didn't get a full answer (or any answer) to the question.

By default, the server closes the connection after eight hours if nothing has happened. You can change the time limit by setting the wait_timeout variable when you start mysqld. See Section 5.1.7, “Server System Variables”.

If you have a script, you just have to issue the query again for the client to do an automatic reconnection. This assumes that you have automatic reconnection in the client enabled (which is the default for the mysql command-line client).

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 does not 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.

    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 Connector/ODBC 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 64MB. 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 B.5.2.9, “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.

  • It is also possible to see this error if host name 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.

You can check whether the MySQL server died and restarted by executing mysqladmin version and examining the server's uptime. If the client connection was broken because mysqld crashed and restarted, you should concentrate on finding the reason for the crash. Start by checking whether issuing the query again kills the server again. See Section B.5.3.3, “What to Do If MySQL Keeps Crashing”.

You can get more information about the lost connections by starting mysqld with the log_error_verbosity system variable set to 3. This logs some of the disconnection messages in the hostname.err file. See Section 5.4.2, “The Error Log”.

If you want to create a bug report regarding this problem, be sure that you include the following information:

See also Section B.5.2.10, “Communication Errors and Aborted Connections”, and Section 1.7, “How to Report Bugs or Problems”.


User Comments
User comments in this section are, as the name implies, provided by MySQL users. The MySQL documentation team is not responsible for, nor do they endorse, any of the information provided here.
  Posted by Mike Kelly on March 17, 2011
I ran into this same error, and as a previous comment noted, and I think bears repeating, was eliminated when I stopped using persistent connections to connect to the MySQL database.
That is, I changed my "PDO::ATTR_PERSISTENT => true" settings to "PDO::ATTR_PERSISTENT => false" and the problem went away.
And there was great rejoicing.
  Posted by MySQL User on May 4, 2011
After I increased my max packet to 2000M, I watched htop when doing the sql import that kept failing and discovered the server went away when I ran out of ram and swap...
  Posted by Chris Calender on May 10, 2011
For those seeing this from PHP scripts, and you've already checked the other items listed above, then ensure your script is calling mysql_free_result when it completes.
  Posted by Jorge Torralba on June 2, 2011
I struggled with this all day. I was uploading two files and then inserting data into the table. The only difference with the files was their size. One would upload just fine and then the database update would take place using a prepared statement. All good. Then I would upload the other larger file which completed uploading but failed to update the database. In the end, what fixed my problem was setting mysqli.reconnect = On in php.ini. My only guess is that the larger file was taking longer to upload thus the db connection was timing out. As a side note, the file was NOT being stored in the db only info about the file.
  Posted by George Liu on August 27, 2011
Just a tip for WHM/Cpanel users experiencing this error it could be related to the WHM cronjob which runs during /scripts/upcp updates which updates WHM/Cpanel versions and checks for version updates to components such as MySQL server http://vbtechsupport.com/433/. Solution is to change when that cronjob is run to not coincide with peak mysql activity time.

  Posted by Radu Onofrei on December 12, 2011
We have found that this problem may occur also because of a bad nameserver, http://matrafox.info/mysql-error-messages-mysql-server-has-gone-away.html or your own cpanel server listed into resolv.conf
  Posted by BOB GALLEY on March 9, 2012
goto include/local
if there is configure.php, delete this file.
  Posted by Pavel Bazanov on June 3, 2013
In my case the problem ("Lost connection to MySQL Server during query") was in a corrupted dump file or in the misbehaving HDDs:

First, I made a dump on the main server and then copied that dump to the replication server. But it seems the replication server had some problems with its HDDs and the dump became corrupted, i.e. MD5 of the original dump file on the main server was different from MD5 of the dump copy on the replication server.
  Posted by Bill Plimpton on August 7, 2013
The key of making it work from command line is not forgetting this part
[mysqld]
max_allowed_packet = 1060M
  Posted by Anna Soseo on October 6, 2014
When you say : If you have a script, you just have to issue the query again for the client to do an automatic reconnection. This assumes that you have automatic reconnection in the client enabled
You can also put automatic reconnection on false to avoid server call. Anna from http://www.howcreateblog.com
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