GCC: -march and -mtune

Some might've noticed that the check-cpu script in the MySQL BUILD directory does not always succeed in detecting the right processor:

roland@roland-laptop:/opt/mysql/5.1/bitkeeper/BUILD$ ./check-cpu
BUILD/check-cpu: Oops, could not find out what kind of cpu this machine is using.

When you dig a little deeper into that script, you will notice that the name of you particular processor (in my case: Intel(R) Core(TM)2 CPU T5600 @ 1.83GHz) is indeed not there and thus not checked. Finally you may find that the model and name of your processor are passed to the gcc compiler.

As far as I cans see the information is used to set the values of the --mtune and --march compiler options. What those are? Hehe! Ok, here's a partial result from man gcc:

-march=cpu-type: Generate instructions for the machine type cpu-type. The choices for cpu-type are the same as for -mtune. Moreover, specifying -march=cpu-type implies -mtune=cpu-type.

Mmm, not sure why -mtune=cpu-type is there in the first place then...

Anybody?

(PS: use /proc/cpuinfo to find out what kind of processor you really have....)

Compiling MySQL From Source on Linux: Check your Tools

I hear a lot of people say: "Well, compiling MySQL from source might pose a problem to Windows users, but it's straight forward for Linux users." Quite often, the difference is explained by claiming that Linux users are used to doing things themselves, and gaining an extra bit of customization by doing so.

My impression is that a large part of the people that say this, are already quite experienced Linux users that are quite comfortable with compiling software from source. The entire toolchain that is involved is already set up on their system, and some of them probably already forgot what they had to do in order for it to make it work.

What is quite often not mentioned is that the required toolchain does not magically land on your system. If you are experiencing prolems compiling MySQL source it's quite likely the toolchain is broken somewhere.

Those that want to compile MySQL from source on Linux: please take some time to read some of the excellent advise from Jay Pipes. Although rather inconspicously titled Making a Corresponding Test Case for your Patch, his HOWTO contains very important information to set up your building environment.

For those that can't wait:

...here are the things you should have installed to avoid headaches:

* automake version 1.9.6
* autoconf version 2.60
* bison version 2.3
* m4 version 1.4.4
* libtool version 1.5.22
...
Note that it is important what order you install these tools! libtool must be installed last to avoid linking with older versions of the other tools. If you don't, you get weird errors.

I'm running Kubuntu Edgy, and I could get packages for all of these things, except one, Bison. I had to compile that one from source too.