Documented in https://enalean.bluespice.cloud/wiki/Enalean_SAS/FarmManagement#Database%20patterns

I have created a new patch for this issue: https://gerrit.wikimedia.org/r/c/mediawiki/extensions/TuleapWikiFarm/+/818065

Now the behaviour is changed! Instead of using a bool useSingleDb, this option is now renamed to centralDb and its value is either a null(default, no central DB is used, each instance gets separate DB), or a string specifying the DB name to be used as central DB. My reasoning was that using the "farm" DB for shared instance DB is not such a good idea anyways, and since there is a need to manually specify which DB should serve as the "central" DB, this makes more sense to me.

Did you a chance to look at this ?

I made a prototype here: https://gerrit.tuleap.net/c/tuleap/+/26427 and I still have a dedicated database that is created instead of prefix.

Plus, in term of migrations, it should be possible to specify/configure a dedicated database instead of the farm one (aka plugin_mediawiki_standalone_farm) because right now the platforms that have "central database" already have their data inside a dedicated DB.

Yes, it would be plugin_mediawiki_standalone_farm, or whatever is set as $wgDBname for the "main instance".

Dejan wrote

This will use "main" DB for all wikis, and having unique dbPrefix for each instance. In this mode, PUT call to instance must contain "dbprefix" param.

Maybe this was not the expectation in the first place?

I maybe should have asked this question first: what do you mean by "main" db ? :) is that plugin_mediawiki_standalone_farm ?

Regarding:

Plus, I find it strange that I don't have to specify the database to use for the single db.

Dejan wrote

This will use "main" DB for all wikis, and having unique dbPrefix for each instance. In this mode, PUT call to instance must contain "dbprefix" param.

Maybe this was not the expectation in the first place?

Regarding:

However, instance creation still creates a plugin_mediawiki_101 database. What did I forget ?

I will check and report back as soon as possible.

@rvogel I have set the following in /etc/tuleap/plugins/mediawiki_standalone/LocalSettings.local.php:

$GLOBALS['wgTuleapFarmConfig']['useSingleDb'] = true;

plus modified plugins/mediawiki_standalone/include/Instance/CreateInstance.php to add dbprefix:

$request = $request_factory->createRequest('PUT', ServerHostname::HTTPSUrl() . '/mediawiki/w/rest.php/tuleap/instance/' . urlencode($this->project->getUnixNameLowerCase()))
            ->withBody(
                HTTPFactoryBuilder::streamFactory()->createStream(
                    \json_encode(
                        [
                            'project_id' => (int) $this->project->getID(),
                            'dbprefix' => 'mw_' . $this->project->getID() . '_',
                        ],
                        JSON_THROW_ON_ERROR
                    )
                )
            );

However, instance creation still creates a plugin_mediawiki_101 database. What did I forget ?

Plus, I find it strange that I don't have to specify the database to use for the single db.

@tgerbet I'd appreciate if you could test this.

Done in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/TuleapWikiFarm/+/809999 Needs proper testing after review

To set "single db" mode, set $wgTuleapFarmConfig['useSingleDb'] = true; This will use "main" DB for all wikis, and having unique dbPrefix for each instance. In this mode, PUT call to instance must contain "dbprefix" param.

DB schema change, tuleap_instances table must be dropped, and maintenance/update.php run, to re-create the table with new schema!