On most systems you can also start mysqld from gdb to get more information if mysqld crashes.
With some older gdb versions on Linux you
run --one-thread if you want to be
able to debug mysqld threads. In this case,
you can only have one thread active at a time.
NPTL threads (the new thread library on Linux) may cause problems while running mysqld under gdb. Some symptoms are:
In this case, you should set the following environment variable in the shell before starting gdb:
LD_ASSUME_KERNEL=2.4.1 export LD_ASSUME_KERNEL
When running mysqld under
gdb, you should disable the stack trace with
--skip-stack-trace to be able to
catch segfaults within gdb.
--gdb option to
mysqld to install an interrupt handler for
SIGINT (needed to stop
^C to set
breakpoints) and disable stack tracing and core file handling.
It is very hard to debug MySQL under gdb if
you do a lot of new connections the whole time as
gdb does not free the memory for old threads.
You can avoid this problem by starting mysqld
thread_cache_size set to a
value equal to
+ 1. In most cases just using
--thread_cache_size=5' helps a
If you want to get a core dump on Linux if
mysqld dies with a SIGSEGV signal, you can
start mysqld with the
--core-file option. This core
file can be used to make a backtrace that may help you find out
why mysqld died:
$> gdb mysqld core gdb> backtrace full gdb> quit
See Section B.3.3.3, “What to Do If MySQL Keeps Crashing”.
If you are using gdb on Linux, you should
.gdb file, with the following
information, in your current directory:
set print sevenbit off handle SIGUSR1 nostop noprint handle SIGUSR2 nostop noprint handle SIGWAITING nostop noprint handle SIGLWP nostop noprint handle SIGPIPE nostop handle SIGALRM nostop handle SIGHUP nostop handle SIGTERM nostop noprint
Here is an example how to debug mysqld:
$> gdb /usr/local/libexec/mysqld gdb> run ... backtrace full # Do this when mysqld crashes
Include the preceding output in a bug report, which you can file using the instructions in Section 1.5, “How to Report Bugs or Problems”.
If mysqld hangs, you can try to use some
system tools like
/usr/proc/bin/pstack to examine where
mysqld has hung.
strace /tmp/log libexec/mysqld
If you are using the Perl
DBI interface, you
can turn on debugging information by using the
trace method or by setting the
DBI_TRACE environment variable.