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 doing. See Section 24.5.1.2, “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's best to use a recent distribution to get the
most updated DBUG manual.
The DBUG package can be used by invoking a program with the
--debug[=
or debug_options]-#
[ option. If
you specify the debug_options]--debug or -#
option without a debug_options value,
most MySQL programs use a default value. The server default is
d:t:i:o,/tmp/mysqld.trace on Unix and
d:t:i:O,\mysqld.trace on Windows. The effect
of this default is:
d: Enable output for all debug macros
t: Trace function calls and exits
i: Add PID to output lines
o,/tmp/mysqld.trace,
O,\mysqld.trace: Set the debug output
file.
Most client programs use a default
debug_options value of
d:t:o,/tmp/,
regardless of platform.
program_name.trace
Here are some example debug control strings as they might be specified on a shell command line:
--debug=d:t --debug=d:f,main,subr1:F:L:t,20 --debug=d,input,output,files:n --debug=d:t:i:O,\\mysqld.trace
For mysqld, it is also possible to change
DBUG settings at runtime by setting the
debug system variable. This
variable has global and session values:
mysql>SET GLOBAL debug = 'mysql>debug_options';SET SESSION debug = 'debug_options';
Changes at runtime require the
SUPER privilege, even for the
session value.
The debug_options value is a sequence
of colon-separated fields:
field_1:field_2:...:field_N
Each field within the value consists of a mandatory flag
character, optionally preceded by a + or
- character, and optionally followed by a
comma-delimited list of modifiers:
[+|-]flag[,modifier,modifier,...,modifier]
The following table describes the permitted flag characters. Unrecognized flag characters are silently ignored.
Flag | Description |
|
Enable output from DBUG_
In MySQL, common debug macro keywords to enable are
|
|
Delay after each debugger output line. The argument is
the delay, in tenths of seconds, subject to machine
capabilities. For example, |
|
Limit debugging, tracing, and profiling to the list of
named functions. An empty list enables all functions.
The appropriate |
| Identify the source file name for each line of debug or trace output. |
| Identify the process with the PID or thread ID for each line of debug or trace output. |
| Identify the source file line number for each line of debug or trace output. |
| Print the current function nesting depth for each line of debug or trace output. |
| Number each line of debug output. |
|
Redirect the debugger output stream to the specified
file. The default output is |
|
Like |
|
Limit debugger actions to specified processes. A
process must be identified with the
|
| Print the current process name for each line of debug or trace output. |
| 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. |
|
Do function |
| 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 compile time option. |
The leading + or -
character and trailing list of modifiers are used for flag
characters such as d or f
that can enable a debug operation for all applicable modifiers
or just some of them:
With no leading + or
-, the flag value is set to exactly the
modifier list as given.
With a leading + or -,
the modifiers in the list are added to or subtracted from
the current modifier list.
The following examples show how this works for the
d flag. An empty d list
enabled output for all debug macros. A nonempty list enables
output only for the macro keywords in the list.
These statements set the d value to the
modifier list as given:
mysql>SET debug = 'd';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | d | +---------+ mysql>SET debug = 'd,error,warning';mysql>SELECT @@debug;+-----------------+ | @@debug | +-----------------+ | d,error,warning | +-----------------+
A leading + or - adds to
or subtracts from the current d value:
mysql>SET debug = '+d,loop';mysql>SELECT @@debug;+----------------------+ | @@debug | +----------------------+ | d,error,warning,loop | +----------------------+ mysql>SET debug = '-d,error,loop';mysql>SELECT @@debug;+-----------+ | @@debug | +-----------+ | d,warning | +-----------+
Adding to “all macros enabled” results in no change:
mysql>SET debug = 'd';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | d | +---------+ mysql>SET debug = '+d,loop';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | d | +---------+
Disabling all enabled macros disables the d
flag entirely:
mysql>SET debug = 'd,error,loop';mysql>SELECT @@debug;+--------------+ | @@debug | +--------------+ | d,error,loop | +--------------+ mysql>SET debug = '-d,error,loop';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | | +---------+
The + and - modifiers
are not always handled correctly and can leave a flag value in
an incorrect state. Verify your
debug-setting sequence in
advance or set it without using + or
-.