TYPO3 Core

→ https://docs.typo3.org/m/typo3/reference-tca/main/en-us/ColumnsConfig/CommonProperties/Mm.html#confval-MM_hasUidField

Sorry, I think I know that, but maybe I got you wrong.

Let's say we do not define the SQL for an MM-relation table because it's not needed anymore:

"The table defined in this property is automatically created by the Database Analyzer starting with v11.4."

mm-Relation with multiple = FALSE
If we have a mm-Relation with multiple = FALSE, we don't set MM_hasUidField.

The Database Analyzer will create a table like this:

fields:

uid_local    int(10) unsigned [0]     
uid_foreign    int(10) unsigned [0]     
sorting    int(10) unsigned [0]     
sorting_foreign    int(10) unsigned [0]     

Indizes

INDEX    uid_local
INDEX    uid_foreign

=> so we wouldn't be compatible with Galera.

If the relations are not multiple it should be possible to add a primary key for:

PRIMARY KEY (uid_local,uid_foreign),

But the install tool doesn't create it like that.

mm-Relation with multiple = TRUE and MM_hasUidField = TRUE
If we have a mm-Relation with multiple = TRUE, we have to set MM_hasUidField = TRUE.
"The table defined in this property is automatically created by the Database Analyzer starting with v11.4."

The Database Analyzer will create a table like this:

fields:

uid    int(10) unsigned Auto-Inkrement     
uid_local    int(10) unsigned [0]     
uid_foreign    int(10) unsigned [0]     
sorting    int(10) unsigned [0]     
sorting_foreign    int(10) unsigned [0]     

Indizes

PRIMARY    uid
INDEX    uid_local
INDEX    uid_foreign

=> so we would be compatible with Galera.

Or should we set - to get compatible with Galera?

multiple = FALSE
MM_hasUidField = TRUE

I'm aware of the issue with MM having no primary key if there is no uid column for a while already, and had a @todo on this in the code for some time.

The workaround for now was exactly as you described: keep 'multiple' false, but set 'MM_hasUidField' true, just to trigger the uid column generation.

We now did some other preparation, and will finally fix this issue in main and v12 now, though. The 'MM_hasUidField' is afterwards obsolete and will be deprecated in v13 with yet another patch.

Patch set 4 for branch main of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/80281

Thanks a lot Christian for your feedback!

We have one week left to check our new server environment, before we will switch to the new hardware plattform, and didn't have any problem with our new Galera environment.
There was one query with an join over an MM-Table where "uid" wasn't unique in the query.
But that's our fault:)

Also our 4 parallel web-servers (4x Apache web-servers, 4x nginx Proxy / cache behind, one Kemp load-balancer) are wortking fine.

Thanks again!

Patch set 1 for branch 12.4 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/80308