Common Errors When Using MySQL Programs 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 5.1.8, “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.3.2.8, “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 may also see the  MySQL server has gone away  error if MySQL is started with the skip_networking  system variable enabled. 5292 •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.