If you have MariaDB compiled for debugging you can both use it in a debugger, like ddd or gdb, and get comprehensive trace files of the execution of MariaDB. The trace files are great to both see the flow of the code and by comparing two trace files you can see the difference in execution.

Core dumps are also much easier to investigate if they come from a debug binary.

Note that a binary compiled for debugging and tracing is about 10-20% slower than a normal binary. If you just compile a binary for debugging (option -g with gcc) the speed difference compared to a normal binary is negligible.

Checking that MariaDB is compiled for debugging

Execute:

mysqld --debug --help

If you get an error 'unknown option '--debug', then MariaDB is not compiled for debugging and tracing.

Building MariaDB for debugging starting from 5.5

On Unix you need to pass -DCMAKE_BUILD_TYPE=Debug to cmake to compile with debug information.

The other option is to use the scripts in the BUILD directory that will compile MariaDB with most common debug options and plugins:

./BUILD/compile-pentium64-debug-max

For the most common configurations there exists a fine-tuned script in the BUILD directory.

If you want to use valgrind, a very good memory instrumentation tool and memory overrun checker, you should use

./BUILD/compile-pentium64-valgrind-max

Some recommended debugging scripts for Intel/AMD are:

BUILD/compile-pentium64-debug-max
BUILD/compile-pentium64-valgrind-max

Building MariaDB 5.3 and older

Here is how you compile with debug on older versions:

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

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-max

The last command will produce a debug version of sql/mysqld. If you have a system other than 64-bit Intel/AMD on Linux you can use a different BUILD/...-debug-max file. If this fails, you can try with:

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

Debugging MariaDB from the source directory

Creating the MariaDB database directory

The following example creates the MariaDB databases in /data.

./scripts/mysql_install_db --srcdir=. --datadir=/data

Running MariaDB in a debugger

The following example is using ddd, an excellent graphical debugger in Linux. If you don't have ddd installed, you can of course use gdb instead.

cd sql
ddd ./mysqld &

In ddd or gdb

run --datadir=/data --language=./share/english --gdb

You can of course set the options in your /.my.cnf file to not have to repeat them on the run line.

If you run mysqld with --debug, you will get a trace file in /tmp/mysqld.trace that shows what is happening.

Note that you can have different options in the configuration file for each MariaDB version (like having a specific language directory).

Debugging MariaDB server with mysql-test-run

If you get a crash while running mysql-test-run you can debug this in a debugger by using one of the following options:

mysql-test-run --gdb failing-test-name

or if you prefer the ddd debugger:

mysql-test-run --ddd failing-test-name

See also

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