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, 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 1.6.1, “MySQL Mailing Lists”. If you believe
that you have found a bug, please use the instructions at
Section 1.7, “How to Report Bugs or Problems”.
In the Windows MySQL distribution,
mysqld.exe
is by default compiled with
support for trace files.
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