Debugging MariaDB
Contents
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.
Building MariaDB 5.3 and older
Here is how you compile with debug on older versions:
Use the scripts in the BUILD directory that will compile MariaDB with most common debug options and plugins, for example:
./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
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
