Using MariaDB with TCMalloc or jemalloc

Using tcmalloc or jemalloc

TCMalloc is a malloc replacement library optimized for multi-threaded usage. It also features a built-in heap debugger and profiler.

Another malloc replacement that may speed up MariaDB is jemalloc.

The procedures to use one of these libraries with MariaDB are the same. Many other malloc replacement libraries (as well as heap debuggers and profilers) can be used with MariaDB in a similar fashion.

Checking the malloc Implementation in Use

If you are unsure which malloc implementation is in use, or if you used one of the procedures explained in this page and you want to verify if it succeeded, you can run this query:

SHOW GLOBAL VARIABLES LIKE 'version_malloc_library';

A value of "system" indicates the system default, which is normally malloc. If another library is used, this query will return the name and version of the library.

Building MariaDB with an alternative to malloc

To build MariaDB 5.5 with TCMalloc, you need to use the following command

cmake -DCMAKE_EXE_LINKER_FLAGS='-ltcmalloc'  -DWITH_SAFEMALLOC=OFF

To use jemalloc, the option should be -ljemalloc.

Starting mariadbd-safe with an alternative to malloc

If you want to do this only one time, as a test, you can also start a standard MariaDB server with TCmalloc with:

/usr/sbin/mariadbd-safe --malloc-lib=tcmalloc

If you want to configure mariadbd-safe to use tcmalloc or jemalloc, edit your configuration file, in the [server] or [mariadbd] group:

malloc-lib=tcmalloc

Starting mariadbd with an alternative to malloc

First, locate the library file that needs to be used:

# jemalloc
find /usr/lib -name "libjemalloc.so.*"
# tcmalloc
find /usr/lib -name "libtcmalloc.so.*"

Now pass it to mariadbd using the LD_PRELOAD variable:

LD_PRELOAD=/path/to/library mariadbd

For example, on OpenSuse 15.4 one would do:

Configuring systemd

If you use systemd to run MariaDB, first locate the library as explained above. The locate the service configuration file:

systemctl status mariadb |grep Loaded

Now edit the mariadb.service file by adding a line to the [Service] group:

Environment=LD_PRELOAD=<path-to-library>

For example:

[Service]
Environment=LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libjemalloc.so.2

Now you should reload the configuration, so that the news setting will take effect, and restart MariaDB:

systemctl daemon-reload
systemctl restart mariadb

Dockerfile

If you run MariaDB on Docker and use an image from a Dockerfile that is publicly available, most probably you have an entrypoint that is a Bash script, which starts mariadbd directly. You can edit this Bash script as explained above. Or you can set the LD_PRELOAD variable from the Dockerfile:

ENV LD_PRELOAD=<path-to-library>

To find the library file you can run one of these commands while the container is running:

# jemalloc
docker exec -ti <container-name> find /usr/lib -name "libjemalloc.so.*"
# tcmalloc
docker exec -ti <container-name> find /usr/lib -name "libtcmalloc.so.*"

Vagrantfile

Usually Vagrant is used to start a complete system in a virtual machine. If this is your case, you can use one of the methods above, for example you can modify your Vagrantfile to copy a modified version of the mariadb.service file into the guest system to configure systemd.

If you use Vagrant with the Docker provider, you can follow the instructions above to modify the Dockerfile.

Finding memory leaks with jemalloc

jemalloc can provide a report of memory leaks at program exit:

MALLOC_CONF=prof_leak:true,lg_prof_sample:0,prof_final:true \
LD_PRELOAD=${JEMALLOC_PATH}/lib/libjemalloc.so.2  path-to-mariadbd

This will produce something like:

<jemalloc>: Leak summary: 267184 bytes, 473 objects, 20 contexts
<jemalloc>: Run jeprof on "jeprof.19678.0.f.heap" for leak detail

You can learn more about the memory leaks with jeprof, that is included with jemalloc:

jeprof --show_bytes path-to-mariadbd jeprof.19678.0.f.heap

You can also generate a PDF call graph of the leak:

jeprof --show_bytes --pdf path-to-mariadbd  jeprof.19678.0.f.heap > /tmp/mariadbd.pdf

See Also

• Profiling memory usage
• Debugging a running server on Linux
• Jemalloc leak checking