Update default datadir for debian to be /var/lib/mariadb

[lvoytek]

Match the existing datadir setting for Debian and Ubuntu, which was changed from /var/lib/mysql to /var/lib/mariadb in 1:11.8.6-5.

Existing Debian patch: https://salsa.debian.org/mariadb-team/mariadb-server/-/blob/debian/latest/debian/patches/set-default-datadir-to-var-lib-mariadb.patch

[CLAassistant]

All committers have signed the CLA.

[gemini-code-assist]

Code Review

This pull request updates the default data directory for Debian-based installations in cmake/install_layout.cmake by changing INSTALL_MYSQLDATADIR_DEB from /var/lib/mysql to /var/lib/mariadb. No review comments were provided for this change, and I have no feedback to provide.

[vuvova]

Questions:

• this is the main branch, so 13.0. A bit too late for Ubuntu?
• what about upgrades 12.3→13.0 ? May be not a problem for Ubuntu, but the change affects our (vendor) packages too.
• How does Ubuntu build MariaDB packages? You likely don't use our autobake.sh script, do you? In that case
  • we can set INSTALL_MYSQLDATADIR=/var/lib/mysql from our autobake.sh and keep the old path in vendor builds and the new path in Ubuntu builds
  • or Ubuntu can set INSTALL_MYSQLDATADIR=/var/lib/mariadb and get a new path without affecting vendor builds. I think the first approach might be easier.
  • or we can change all, Ubuntu and vendor, builds, and then pre/post-inst scriptlets need to handle the upgrade and move the data to the new location

@ottok, what do you think?

[grooverdan]

Thanks @lvoytek

Questions:

* this is the `main` branch, so 13.0. A bit too late for Ubuntu?

Ubuntu 26.04 already carrying the patch for 11.8_+
bugs.launchpad.net/ubuntu/+source/mariadb/+bug/2148632

* what about upgrades 12.3→13.0 ? May be not a problem for Ubuntu, but the change affects our (vendor) packages too.

I opened https://jira.mariadb.org/browse/MDEV-39461

But yes, we'll need the scripts too.

* How does Ubuntu build MariaDB packages? You likely don't use our `autobake.sh` script, do you? In that case

Like Debian - straight from debian/rules

  * we can set `INSTALL_MYSQLDATADIR=/var/lib/mysql` from our `autobake.sh` and keep the old path in vendor builds and the new path in Ubuntu builds
  * or Ubuntu can set `INSTALL_MYSQLDATADIR=/var/lib/mariadb` and get a new path without affecting vendor builds. I think the first approach might be easier.
  * or we can change all, Ubuntu and vendor, builds, and then pre/post-inst scriptlets need to handle the upgrade and move the data to the new location

I do like the last plan.

Question is, do we stop on Deb changes or include RPM too?

@ottok, what do you think?

Its already in Debian sid.

https://salsa.debian.org/mariadb-team/mariadb-server/-/merge_requests/155

I was hoping to see more of the script changes from that here.

Having a modified subset in 11.8 to handle Ubuntu upgrade to our vendor ones would be good too to solve MDEV-39461. Probably like a earlier version in salsa merge request 155 that dropped the config file in the post install without changing the default.

[gkodinov]

This is a preliminary review. Can you please describe the problem you're solving? I.e. what happens now and how is that wrong. And how your solution goes about solving the problem, i.e. how is the current behavior modified.
Ideally this should happen in an MDEV prior to submitting a PR for it, but I can also file one for you if you put your rationale into the PR itself.

[ottok]

If I am not mistaken, the submitter of this patch (Canonical employee) had some discussions with Sergei about switching the datadir to /var/lib/mariadb in MariaDB. This submission does that, and targets main to be in the next upstream MariaDB release.

This was already included in Debian and Ubuntu 1:11.6.8. The commit https://salsa.debian.org/mariadb-team/mariadb-server/-/commit/2bf6f4d3e1cb090ad5ba7f443ae02af5047c5391 in Debian is a bit more verbose than the commit message/description in this PR.

I approved this change in Debian with the assumption that upstream will eventually follow in some future version. This PR only updates the _DEB variable but you might as well also update the equivalent _RPM variable.

From my point of view this would be fine to merge as-is, and perhaps MariaDB devs can follow-up with whatever additional changes are needed to make /var/lib/mariadb the default datadir on all new (fresh) installations?

Upgrades of old installs will continue to use /var/lib/mysql, at least with how the package maintainer scripts are done in Debian/Ubuntu.

[vuvova]

I like this 99-legacy-datadir.cnf technique, if we adopt that we can change the default indeed.

@lvoytek, your commit in Debian changes a lot more than this PR, are the other changes needed? Why did you omit them here?