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
Section 1.7.1, “MySQL Mailing Lists”. If you believe that you have
found a bug, please use the instructions at
Section 1.8, “How to Report Bugs or Problems”.
In the Windows MySQL distribution, mysqld.exe
is by default compiled with support for trace files.
