Limitations

Limitations

Microcontrollers by their nature have limited memory and limited processing power. Despite that, you can achieve quite a lot with the Arduino platform. However, there are real limits of what can be done within the limited memory and processing power of the Arduino platform wit respect to memory intensive or processor intensive applications such as network clients.

Thus, it may come as no surprise that the Connector/Arduino library has a number of limitations that place bounds on what is possible with such limited hardware. The following lists the major limitations of the library for you to consider when building you own MySQL client sketches. While some of these may be mitigated by using a "bigger" Arduino, you should consider these the upper bounds for what is possible on the more popular Arduino boards.

• Query strings (the SQL statements) must fit into memory. The connector uses an internal buffer for building data packets to send to the server. However, the library supports the use of PROGMEM strings.
• Similarly, the combined length of a row returned from the server (data size in bytes) must fit into memory. Attempting to read a row from a table with 250 columns of integers isn't going to work. Keep your results sets as narrow (fewest columns) as possible and use a WHERE clause to limit the number of rows returned.
• Result sets from SELECT (for example) queries must be read starting with fetching the columns then the complete rows one row at a time and one field at a time. Failure to do so will result in mysterious packet errors (because you didn't read all of the data).
• Server error responses are processed immediately if and only if the #debug directive is defined. If so, the connector prints the error code and message to the serial monitor otherwise, the errors may be suppressed.
• The connector is written to support the current and recent releases of MySQL from Oracle Corporation. While there are variants maintained by other vendors, they may have some modifications that introduce subtle incompatibilities. If you encounter strange errors or issues using the connector with your MySQL server, ensure you are using the server binaries distributed by Oracle.
• For newer versions of MySQL that use the newest security plugins, you must use the mysql_native_password plugin for any user you want to use with the connector. The connector does not support the latest authentication plugins.
• The connector is written to adhere to the Arduino Ethernet (and compatible WiFi) class libraries. If you plan to use a shield that comes with its own library, be sure to check that it is 100% compatible (has same classes and methods). Otherwise, you will not be able to use the connector with that shield without modification.