Cry MySQL How to...
Troubleshooting the error: ERROR [HY000] [MySQL][ODBC 3.51
Driver]Can't connect to MySQL server on 'localhost' (10048)
When connecting to a MySQL database through ODBC the following error
ERROR [HY000] [MySQL][ODBC 3.51 Driver]Can't connect to MySQL server
on 'localhost' (10048)
The precise presentation of this error may vary according to the
software used, this wording was generated from an ASP.NET application.
- The application has previously been able to successfully connect
to the database.
- Waiting a minute or so, and the application can connect again
without the error.
- The error seems to manifest itself under "stress" conditions,
when lots of connections are being made opened and closed in a short
space of time (minutes).
These notes only apply to the error above when the "other symptoms"
The error is caused not by MySQL or the MySQL ODBC driver, but by the
behaviour of Windows. For performance reasons Windows maintains a
connection on a TCP port after it is closed for (by default) 4 minutes.
The advantage of this is that if the connection needs to be reopened it
can be done at a lower cost. The trouble is that under heavy load when
lots of connections are opened and closed to the database, the system
can hit a limit on the maximum number of connections allowed (even
though as far as the application is concerned these connections have
- To decrease the delay before Windows releases an open TCP
connection, use regedit to edit the following registry value of:
This value does not exist by default and will need to be created. It
should be a DWORD. The valid range is 0x1E - 0x12C (30seconds to 300
seconds), the default is 0xF0 (240 seconds).
Decreasing the value of TcpTimedWaitDelay should help, but is
unlikely to permanently solve the problem for a busy system (because
if the system is busy the limits will still be hit).
- Consider whether it is possible to modify the application to
re-use database connections instead of closing and reopening them.
In theory enabling connection pooling would address this problem.
For more information about connection pooling see
To enable connection pooling for the MySQL driver:
- Start > Control Panel > Administrative Tools > Data Sources
This will open up the "ODBC Data Source Administrator".
- On the "Connection Pooling" tab, double click the ODBC
Driver you are using to connect to MySQL.
This will open up the "Set Connection Pooling Attributes"
- To enable pooling select "Pool Connections to this driver"
These notes have been tested against MySQL version 4.1
and 5.0 with version 3.51 of the ODBC driver.
About the author: Brian Cryer
is a dedicated software developer and webmaster. For his day job he develops websites and desktop applications as well as providing IT services. He moonlights as a technical author and consultant.