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):
|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
wait_timeout variable when you
start mysqld. See
Section 5.2.2, “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 (or the db administrator) has killed the running thread
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.
You got a timeout from the TCP/IP connection on the client
side. This may happens 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
wait_timeout expired) before the command
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 connection.
In this case, even if 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.2.9, “
Packet too large”.
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.
You may also see the
MySQL server has gone
away error if MySQL is started with the
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 A.4.2, “What to Do If MySQL Keeps Crashing”.
You can get more information about the lost connections by
starting mysqld with the
option. This logs some of the disconnected errors in the
hostname.err file. See
Section 5.11.2, “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 A.4.2, “What to Do If MySQL Keeps Crashing”.
If a specific query kills mysqld and the
tables involved were checked with
TABLE before you ran the query, can you provide a
reproducible test case? See
Section E.1.6, “Making a Test Case If You Experience Table Corruption”.
What is the value of the
system variable in the MySQL server? (mysqladmin
variables gives you the value of this variable.)
Have you tried to run mysqld with the
--log option to determine whether the
problem query appears in the log?
See also Section A.2.10, “Communication Errors and Aborted Connections”, and
Section 1.8, “How to Report Bugs or Problems”.