(mysql.info) compiling-for-debugging

 
 E.1.1 Compiling MySQL for Debugging
 -----------------------------------
 
 If you have some very specific problem, you can always try to debug
 MySQL. To do this you must configure MySQL with the -with-debug or the
 -with-debug=full option. You can check whether MySQL was compiled with
 debugging by doing: `mysqld --help'. If the -debug flag is listed with
 the options then you have debugging enabled.  `mysqladmin ver' also
 lists the `mysqld' version as `mysql ...  --debug' in this case.
 
 If you are using `gcc' or `egcs', the recommended `configure' line is:
 
      CC=gcc CFLAGS="-O2" CXX=gcc CXXFLAGS="-O2 -felide-constructors \
         -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql \
         --with-debug --with-extra-charsets=complex
 
 This avoids problems with the `libstdc++' library and with C++
 exceptions (many compilers have problems with C++ exceptions in
 threaded code) and compile a MySQL version with support for all
 character sets.
 
 If you suspect a memory overrun error, you can configure MySQL with
 -with-debug=full, which installs a memory allocation (`SAFEMALLOC')
 checker. However, running with `SAFEMALLOC' is quite slow, so if you
 get performance problems you should start `mysqld' with the
 -skip-safemalloc option. This disables the memory overrun checks for
 each call to `malloc()' and `free()'.
 
 If `mysqld' stops crashing when you compile it with -with-debug, you
 probably have found a compiler bug or a timing bug within MySQL. In
 this case, you can try to add -g to the `CFLAGS' and `CXXFLAGS'
 variables above and not use -with-debug. If `mysqld' dies, you can at
 least attach to it with `gdb' or use `gdb' on the core file to find out
 what happened.
 
 When you configure MySQL for debugging you automatically enable a lot
 of extra safety check functions that monitor the health of `mysqld'. If
 they find something `unexpected,' an entry is written to `stderr',
 which `mysqld_safe' directs to the error log! This also means that if
 you are having some unexpected problems with MySQL and are using a
 source distribution, the first thing you should do is to configure
 MySQL for debugging! (The second thing is to send mail to a MySQL
 mailing list and ask for help. See  mailing-lists. If you
 believe that you have found a bug, please use the instructions at 
 bug-reports.
 
 In the Windows MySQL distribution, `mysqld.exe' is by default compiled
 with support for trace files.
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