Re: Error 1064 Duplicate entry 'ndbcluster-96' for key 'tables.engine'

[Duarte Patricio]

Hello,

To request that kind of support, you must go through Oracle MySQL Support.

> I dunno how to do these procedures please kindly give me example:
> - quote yours:"you can always do a fresh-reset on MySQL server which does clean every entry in DD."

A fresh-reset is done by (after backup of everything): `$ mysqld <all-other-options> --initialize`. One must remove data directory contents. See the manual for more information, such as here: https://dev.mysql.com/doc/refman/8.0/en/data-directory-initialization.html

When talking about restarting each MySQL server, is really just the MySQL server and not the storage engine (NDB). One by one.

I don't know how the deployment is setup, but there should be a server (NDB, MGM or MySQL) per VM/container. So, a restart of MySQL (with --initialize), one by one, should let that fresh MySQL server sync the NDB data dictionary with the MySQL data dictionary properly. On each restart, one should wait for the server to be stable. Then proceed to the next one.

As for upgrades, data is not lost if it is safely stored, although backups are always important. Although, if you delete the VM/container where that old server is run from, then yes *data is lost because it is there in the filesystem*. So on that case, backup/copy-to-safe-location/restore is the safe option. And a staging/dev environment to test the upgrade steps.