This section also covers the related
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
|The client couldn't send a question to the server.|
|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
variable when you start mysqld. See
Section 5.1.3, “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
Some other common reasons for the
MySQL server has
gone away error are:
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_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
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
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
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 B.5.2.10, “Packet Too Large”.
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
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 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
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.5.4.2, “What to Do If MySQL Keeps Crashing”.
You can get more information about the lost connections by
starting mysqld with the
--log-warnings=2 option. This
logs some of the disconnected errors in the
hostname.err file. See
Section 5.3.1, “The Error Log”.
If you want to create a bug report regarding this problem, be sure that you include the following information:
Indicate whether the MySQL server died. You can find information about this in the server error log. See Section B.5.4.2, “What to Do If MySQL Keeps Crashing”.
If a specific query kills mysqld and
the tables involved were checked with
CHECK TABLE before you ran
the query, can you provide a reproducible test case? See
Section 18.4, “Porting to Other Systems”.