MULTI_ABS() UDF function

This is a MySQL UDF which does multiple ABS() calls to pairs of the arguments and accumulates the result.

How to build it

Development mode

If you want to change the function often for development purposes than a multi stage Dockerfile is not the best option because the base image which should include the GCC toolchain will be built every time. For this reason, there is a Dockerfile.base . To build the base image just run make build-base. After that every time you want to build after code change just run make build. Then Dockerfile and not Dockerfile.base will be used and the .so file called multiabs_udf.so will be created and copied into /usr/lib/mysql/plugin/ where MySQL (in the standard container) looks for plugins.

Non-development mode

When you just want to compile once (or rarely, in case of CI/CD) the function then you should modify the Dockerfile and remove the usage of a base image and just build it on the fly. To elaborate more. To switch from development mode:

# This should be the real code (found in Dockerfile.base) after the development has finished. 
# A base container can be cached and thus the image building will be really quick
#
#FROM mysql:8.0 as udf_layer
#
#RUN apt-get update && apt-get install -y \
#    gcc file\
#	libmysqlclient-dev \
#    && apt-get clean \
#    && rm -rf /var/lib/apt/lists/*
	
FROM multiabs_mysql_base:8.0 as udf_layer
...

to non-development, you should have this:

# This should be the real code (found in Dockerfile.base) after the development has finished. 
# A base container can be cached and thus the image building will be really quick

FROM mysql:8.0 as udf_layer

RUN apt-get update && apt-get install -y \
    gcc file\
	libmysqlclient-dev \
    && apt-get clean \
    && rm -rf /var/lib/apt/lists/*
	
...

Steps

• make build-base (in case you are developing)
• make build to build the containers
• make container-start to start the newly built container which contains the UDF
• make container-logs in case you want to see the stdout of the container
• make container-kill kills the container. Later it needs to be removed/destroyed
• make container-destroy to remove the container
• make function-create to create/load the function
• make function-test to run rudimentary test queries agains the functin
• make function-drop to drop/unload the function

If you want to skip the container-kill and container-destroy commands just pass -rm to docker in step container-start. The container opens local port 3306 which the function-* targets use with local MySQL CLI which you need to have installed in the host OS.

After a change to multiabs_udf.so

• If you have a container already running execute make container-kill container-destroy
• make build container-start to rebuild the container and start it. Then run make function-test. Normally you need to run make function-create only once and that is after your first build or you have removed your MySQL datadir. If the datadir is reused from a previous run the UDF will be loaded automagically by MySQL on server start (container) start.

Examples

MULTI_ABS() returns 0 MULTI_ABS(3, 8) returns 5 MULTI_ABS(3, 8, 12, 25) returns ABS(3,8)+ABS(12,25) = 18

MULTI_ABS(3) will error because the argument count is odd MULTI_ABS(3,5,8) will error because the argument count is odd