Debugging a MySQL Server When running  mysqld  under  gdb , you should disable the stack trace with  --skip-stack-trace  to be able to catch segfaults within  gdb . Use the  --gdb  option to  mysqld  to install an interrupt handler for  SIGINT  (needed to stop  mysqld  with ^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  with thread_cache_size  set to a value equal to  max_connections  + 1. In most cases just using  -- thread_cache_size=5’  helps a lot! 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: See Section B.3.3.3, “What to Do If MySQL Keeps Crashing” . If you are using  gdb  on Linux, you should install a  .gdb  file, with the following information, in your current directory: Here is an example how to debug  mysqld : Include the preceding output in a bug report, which you can file using the instructions in Section 1.6, “How to Report Bugs or Problems” . If  mysqld  hangs, you can try to use some system tools like  strace  or  /usr/proc/bin/pstack  to examine where  mysqld  has hung. 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. On some operating systems, the error log contains a stack trace if  mysqld  dies unexpectedly. You can use this to find out where (and maybe why)  mysqld  died. See Section 5.4.2, “The Error Log” . To get a stack trace, you must not compile  mysqld  with the  -fomit-frame-pointer  option to gcc. See Section 5.9.1.1, “Compiling MySQL for Debugging” . A stack trace in the error log looks something like this: 5.9.1.5 Using a Stack Trace 1156 strace /tmp/log libexec/mysqld shell>  gdb /usr/local/libexec/mysqld gdb> run ... backtrace full # Do this when mysqld crashes 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 shell>  gdb mysqld core gdb> backtrace full gdb> quit