23.4.3. The DBUG Package

The MySQL server and most MySQL clients are compiled with the DBUG package originally created by Fred Fish. When you have configured MySQL for debugging, this package makes it possible to get a trace file of what the program is debugging. See Section 23.4.1.2, "Creating Trace Files".

This section summarizes the argument values that you can specify in debug options on the command line for MySQL programs that have been built with debugging support. For more information about programming with the DBUG package, see the DBUG manual in the dbug directory of MySQL source distributions. It is best to use a recent distribution to get the most updated DBUG manual.

You use the debug package by invoking a program with the --debug="..." or the -#... option.

Most MySQL programs have a default debug string that is used if you don't specify an option to --debug. The default trace file is usually /tmp/program_name.trace on Unix and \program_name.trace on Windows.

The debug control string is a sequence of colon-separated fields as follows:

<field_1>:<field_2>:...:<field_N>

Each field consists of a mandatory flag character followed by an optional "," and comma-separated list of modifiers:

flag[,modifier,modifier,...,modifier]

The following table shows the currently recognized flag characters.

Flag	Description
`d`	Enable output from DBUG_<N> macros for the current state. May be followed by a list of keywords which selects output only for the DBUG macros with that keyword. An empty list of keywords implies output for all macros.
`D`	Delay after each debugger output line. The argument is the number of tenths of seconds to delay, subject to machine capabilities. For example, `-#D,20` specifies a delay of two seconds.
`f`	Limit debugging, tracing, and profiling to the list of named functions. Note that a null list disables all functions. The appropriate `d` or `t` flags must still be given; this flag only limits their actions if they are enabled.
`F`	Identify the source file name for each line of debug or trace output.
`i`	Identify the process with the PID or thread ID for each line of debug or trace output.
`g`	Enable profiling. Create a file called `dbugmon.out` containing information that can be used to profile the program. May be followed by a list of keywords that select profiling only for the functions in that list. A null list implies that all functions are considered.
`L`	Identify the source file line number for each line of debug or trace output.
`n`	Print the current function nesting depth for each line of debug or trace output.
`N`	Number each line of debug output.
`o`	Redirect the debugger output stream to the specified file. The default output is `stderr`.
`O`	Like `o`, but the file is really flushed between each write. When needed, the file is closed and reopened between each write.
`p`	Limit debugger actions to specified processes. A process must be identified with the `DBUG_PROCESS` macro and match one in the list for debugger actions to occur.
`P`	Print the current process name for each line of debug or trace output.
`r`	When pushing a new state, do not inherit the previous state's function nesting level. Useful when the output is to start at the left margin.
`S`	Do function `_sanity(_file_,_line_)` at each debugged function until `_sanity()` returns something that differs from 0.
`t`	Enable function call/exit trace lines. May be followed by a list (containing only one modifier) giving a numeric maximum trace level, beyond which no output occurs for either debugging or tracing macros. The default is a compiletime option.

Some examples of debug control strings that might appear on a shell command line (the -# is typically used to introduce a control string to an application program) are:

-#d:t-#d:f,main,subr1:F:L:t,20-#d,input,output,files:n-#d:t:i:O,\\mysqld.trace

In MySQL, common tags to print (with the d option) are enter, exit, error, warning, info, and loop.