4.9 Debugging Stored Procedures and Functions

The stored procedure debugger, provides facilities for setting breakpoints, stepping into individual statements (Step Into, Step Out, Step Over), evaluating and changing local variable values, evaluating breakpoints, and other typical debugging tasks.


This feature is available as of MySQL Connector/Net 6.6.

Installing the Debugger

To enable the stored procedure debugger:


The debugger recreates at the start of each debug session a serversidedebugger database in your server. This database helps to track the instrumented code and implement observability logic in the debugged routine. Your current connection needs to have privileges to create that database, and its associated stored routines, functions, and tables.

The debugger makes changes behind the scenes to temporarily add instrumentation code to the stored routines that you debug. You must have the ALTER ROUTINE privilege for each stored procedure, function, or trigger that you debug. (Including procedures and functions that are called, and triggers that are fired, by a procedure that you are debugging.)

Starting the Debugger

To start the debugger, follow these steps:

At this point, Visual Studio switches to debug mode, opening the source code of the routine being debugged in step mode, positioned on the first statement.

If the initial routine you debug has one or more arguments, a pop-up will show up with a grid (a row per each argument and three columns: one for the argument, one for the argument value (this is editable) and one for nullifying that argument value (a checkbox)). After setting up all the argument values, you can press OK to start the debug session, or Cancel to cancel the debug session.

Figure 4.21 Setting Arguments (1 of 2)

Setting Arguments (1 of 2)

Figure 4.22 Setting Arguments (2 of 2)

Setting Arguments (2 of 2)

How the Debugger Works

To have visibility into the internal workings of a stored routine, the debugger prepares a special version of the procedure, function, or trigger being debugged, instrumented with extra code to keep track of the current line being stepped into and the values of all the local variables. Any other stored procedures, functions, or triggers called from the routine being debugged are instrumented the same way. The debug versions of the routines are prepared for you automatically, and when the debug session ends (by either pressing F5 or Shift + F5), the original versions of the routines are automatically restored.

A copy of the original version of each instrumented routine (the version without instrumentation) is stored in the AppData\Roaming\MySqlDebuggerCache folder for the current Windows user (the path returned by calling System.Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) in .NET, plus appending MySqlDebuggerCache. There is one file for each instrumented routine, named routine_name.mysql. For example, in Windows 7, for a user named fergs, the path is C:\Users\fergs\AppData\Roaming\MySqlDebuggerCache.

Two threads are used, one for the debugger and one for the routine being debugged. The threads run in strict alternation, switching between the debugger and the routine as each statement is executed in the stored routine.

Basic Debugging Operations

The debugger has the same look and feel as the standard Visual Studio debuggers for C#, VB.NET or C++. In particular, the following are true:

Locals and Watches

Call Stack



Other Features


Keyboard Shortcuts

The following list summarizes the keyboard shortcuts for debugging: