How to produce a full stack trace for mysqld (The MariaDB server) - Source

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Revision: 6991
User: Michael Widenius
Date: 2011-10-16 11:03

<<toc>>
When <<fixed>>mysqld<</fixed>> fails hard (core dump) it will by
default write a stack trace in the <<fixed>>'hostname'.err<</fixed>>
file in the database directory.  In some cases this is however not
enough to find out exactly where the problem.

The following instructions is how to produce a full stack trace on Unix.

To be able to exactly pinpoint where the problem is a MariaDB
developer would need one or more of the following:

* A full stack trace (that one can only get from a binary compiled with
  debugging)
* A core file (an image of the crashed program)
* A mysqld compiled for debugging.

The steps to create the above are:

* Download a [[http://downloads.askmonty.org/mariadb|source tar.gz file]] (like <<fixed>>mariadb-5.2.9.tar.gz<</fixed>>).
* Compile it for debugging
* Update your .my.cnf file to ensure you get a <<fixed>>core<</fixed>> and stack trace.
* Install the debug version instead of your normal one.
* Run with the debug version until you get a new crash.
* Restore your old <<fixed>>mysqld<</fixed>> version.

== Compiling MariaDB for debugging

Here is an example of how to compile MariaDB for debugging in our home
directory with MariaDB 5.2.9 as an example:

<<code>>
cd ~
mkdir mariadb
cd mariadb
tar xvf mariadb-5.2.9.tar.gz
ln -s mariadb-5.2.9 current
cd current
./BUILD/compile-pentium64-debug
<</code>>

The last command will produce a debug version of
<<fixed>>sql/mysqld<</fixed>>.  If you have another system than 64 bit
Intel/Amd on Linux you can use another <<fixed>>BUILD/...-debug<</fixed>>
file. If this fails, you can try with:

<<code>>
./BUILD/autorun.sh
./configure --with-debug=full -with-extra-charsets=complex \
--with-plugin-aria --with-aria-tmp-tables --without-plugin-innodb_plugin \
--with-mysqld-ldflags=-all-static  --with-client-ldflags=-all-static 
make
<</code>>

== Updating your my.cnf

Add the following last to your <<fixed>>~~/.my.cnf<</fixed>> file:

<<code>>
[[mysqld]]
--stack-trace
--core-file
[[mysqld-safe]]
--core-file-size=unlimited
<</code>>

These are safe to leave there also in the future.

Note that if you are using <<fixed>>safe_mysqld<</fixed>> and running
<<fixed>>mysqld<</fixed>> as <<fixed>>root<</fixed>>, then no
<<fixed>>core<</fixed>> file is created on some systems. The solution
is to run <<fixed>>mysqld<</fixed>> as another user.

== Temporary replacing your standard mysqld with the debug version

This is how you do it on Open SuSE. Other version may have a different
place for where <<fixed>>mysqld<</fixed>> is stored.

<<code>>
mysqladmin shutdown
cd /usr/local/mysql/libexec
mv mysqld mysqld-org
cp ~/mariadb/current/sql/mysqld mysqld-debug
ln -s mysqld-debug mysqld
<</code>>

The above replaced your mysqld version with the debug version, but so
that it's trivial for your to revert back to your original version.

And then start mysqld again (normally with something like
<<code>>
/etc/rc.d/mysql start
<</code>>

== Restoring your original mysqld version

If you want to restore your old version that you replaced above, you do it with:
<<code>>
cd /usr/local/mysql/libexec
rm mysqld
ln -s mysqld-org mysqld
<</code>>

== Using the core file

If the debug version of mysqld crashes, you should now have:

* A more precise stack trace in the <<fixed>>'hostname'.err<</fixed>> in the data directory.
* A <<fixed>>core<</fixed>>, <<fixed>>core.####<</fixed>> file in your data directory.

To examine the stack trace and other information in the
<<fixed>>gdb<</fixed>> debugger you can do:

<<code>>
cd ~/mariadb/current
cp mariadb-database-directory/core* core
gdb ~/mariadb/current/sql/mysqld core
backtrace full
<</code>>

== Running a copy of the database directory

If you are concerned with running the debug binary on your production
database you can also copy the database to another location and use
the new debug version with this.  In this case you can skip the above
instructions of installing MariaDB and instead
[[running-mariadb-from-the-source-directory|run mysqld directly from
the source directory]].

This is useful when you know which statement crashed the server.

Just start mysqld with the option
<<fixed>>--datadir=/copy-of-original-data-directory<</fixed>>

== Reporting the problem

[[reporting-bugs|Report the problem]], including the stack information in the
[[https://bugs.launchpad.net/maria|MariaDB bugs database]].

For very difficult or critical errors, you should consider
[[ftp|sending]] the debug version of <<fixed>>mysqld<</fixed>> and the
<<fixed>>core<</fixed>> file and some information of how to contact you
in a <<fixed>>.tar<</fixed>> or <<fixed>>.zip<</fixed>> file to the
MariaDB developers at Monty Program Ab so that we can analyze it and
try to produce a fix.

Content reproduced on this site is the property of its respective owners, and this content is not reviewed in advance by MariaDB. The views, information and opinions expressed by this content do not necessarily represent those of MariaDB or any other party.

How to produce a full stack trace for mysqld (The MariaDB server) - Source

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