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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 must use 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. We recommend you
to upgrade to gdb 5.1 ASAP as thread debugging works much better with this
version!
When running mysqld
under gdb, you should disable the stack trace
with --skip-stack-trace
to be able to catch segfaults within gdb.
In MySQL 4.0.14 and above you should use the --gdb
option to
mysqld. This will install an interrupt handler for SIGINT
(needed
to stop mysqld with ^C
to set breakpoints) and disable stack
tracing and core file handling.
It's very hard to debug MySQL under gdb
if you do a lot of
new connections the whole time as gdb
doesn't free the memory for
old threads. You can avoid this problem by starting mysqld
with
-O thread_cache_size= 'max_connections +1'
. In most cases just
using -O thread_cache_size=5'
will help 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:
shell> gdb mysqld core gdb> backtrace full gdb> exit |
See section A.4.1 What To Do If MySQL Keeps Crashing.
If you are using gdb 4.17.x or above on Linux, you should install a `.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 |
If you have problems debugging threads with gdb, you should download gdb 5.x and try this instead. The new gdb version has very improved thread handling!
Here is an example how to debug mysqld:
shell> gdb /usr/local/libexec/mysqld gdb> run ... backtrace full # Do this when mysqld crashes |
Include the above output in a mail generated with mysqlbug
and
mail this to the general MySQL mailing list.
See section 1.7.1.1 The MySQL Mailing Lists.
If mysqld
hangs you can try to use some system tools like
strace
or /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.
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