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B.1.2.10. Communication Errors and Aborted Connections

The server error log can be a useful source of information about connection problems. See 項4.11.2. 「エラー ログ」. If you start the server with the --log-warnings option, you might find messages like this in your error log: 

010301 14:38:23  Aborted connection 854 to db: 'users' user: 'josh'

If Aborted connections messages appear in the error log, the cause can be any of the following:

  • The client program did not call mysql_close() before exiting.

  • The client had been sleeping more than wait_timeout or interactive_timeout seconds without issuing any requests to the server. See 項4.2.3. 「システム変数」.

  • The client program ended abruptly in the middle of a data transfer.

When any of these things happen, the server increments the Aborted_clients status variable.

The server increments the Aborted_connects status variable when the following things happen:

  • A client doesn't have privileges to connect to a database.

  • A client uses an incorrect password.

  • A connection packet doesn't contain the right information.

  • It takes more than connect_timeout seconds to get a connect packet. See 項4.2.3. 「システム変数」.

If these kinds of things happen, it might indicate that someone is trying to break into your server!

MySQL Enterprise.  For reasons of security and performance the advisors provided by the MySQL Network Monitoring and Advisory Service pay special attention to the Aborted_connections status variable. For more information see, http://www.mysql.com/products/enterprise/advisors.html.

Other reasons for problems with aborted clients or aborted connections:

  • Use of Ethernet protocol with Linux, both half and full duplex. Many Linux Ethernet drivers have this bug. You should test for this bug by transferring a huge file via FTP between the client and server machines. If a transfer goes in burst-pause-burst-pause mode, you are experiencing a Linux duplex syndrome. The only solution is switching the duplex mode for both your network card and hub/switch to either full duplex or to half duplex and testing the results to determine the best setting.

  • Some problem with the thread library that causes interrupts on reads.

  • Badly configured TCP/IP.

  • Faulty Ethernets, hubs, switches, cables, and so forth. This can be diagnosed properly only by replacing hardware.

  • The max_allowed_packet variable value is too small or queries require more memory than you have allocated for mysqld. See 項B.1.2.9. 「Packet too large」.

See also 項B.1.2.8. 「MySQL server has gone away」.