feat: add the option to specify delayed replication for MariaDB

[dmitryvk]

Delayed replication is very useful for testing various replication scenarios.

[fauust]

Hi @dmitryvk ! Thank you for this contribution. It looks like something quite useful indeed.
Do you think that this could be tested somehow in the context of the GitHub CI? Also, it probably needs some documentation?

[dmitryvk]

Do you think that this could be tested somehow in the context of the GitHub CI?

It should be possible, I'll see if I can add some tests for it.

Also, it probably needs some documentation?

That would also be useful. I've only been able to find https://mariadb.com/kb/en/mariadb-server-docker-official-image-environment-variables/ as the documentation source, but I don't know how to make a PR/suggestions for it.

[grooverdan]

Before we go to far on tests/documentation, if we look at the change master to options there's a significant amount of options that are just passed though.

Unfortunately environment arrays aren't supported in OCI. As this is passed straight though to change master to can we just make MARIADB_REPLICATION_OPTIONS as pass that as a straight string on the CHANGE MASTER SQL? If there's a good reason why not, please say so. The trouble with defining interfaces is they become rather fixed. Good design consideration is rather important.

If we where considering a FOR CHANNEL option I think this would be a bit different (as it would imply multiple replication channels and each would have its own distinct options. I'm not saying we include this, just noting the bounds of the feature request.

On test cases: .test/run.sh to be expanded and just change show replica status and check the output for the string.

On documentation - yes that is the right source. There's no source control. It can be edited by anyone who creates and account, but if you don't want to do that just leaving some text here and I'll include it would be much appreciated.

[grooverdan]

Happy with this concept?

If so I'll near to clear out the default MASTER_CONNECT_RETRY too.

[dmitryvk]

I think this idea (of passing through additional parameters via a single env variable) is really good.
I haven't had the time to update the PR myself yet; if you intend to do it yourself - I would be perfectly happy.