clarify collations are also supported for db_charset

[mcrauwel]

Description

This is a documentation change to clarify the ability to configure a specific collation in case your environment runs different MySQL version where different character sets might have different collation, in which case replication might break

Related Issue(s)

Fixed #16422

Checklist

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• Documentation was added or is not required

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 68.61%. Comparing base (fab9071) to head (f090948).
Report is 3 commits behind head on main.

Files	Patch %	Lines
go/vt/dbconfigs/dbconfigs.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16423      +/-   ##
==========================================
- Coverage   68.63%   68.61%   -0.02%     
==========================================
  Files        1551     1551              
  Lines      199515   199515              
==========================================
- Hits       136938   136907      -31     
- Misses      62577    62608      +31     

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[deepthi]

Looks fine to me. The endtoend tests need to be fixed, they capture flag help output.
Most likely just vttablet.txt, but the test failure will tell you.

[deepthi]

Most likely just vttablet.txt, but the test failure will tell you.

There are 5 binaries which are affected, so the 5 corresponding files need to change under go/flags/endtoend.

[shlomi-noach]

🌷

[dbussink]

I think we probably want to drop the Make sure bit since for anyone running MySQL 8 and later (which is the only supported version), the default is fine and doesn't need configuring.

[deepthi]

What are you proposing? Drop the entire second sentence? Can you post that as a suggestion so that it is clearer?

[mcrauwel]

@dbussink FWIW, I kept the wording vague not mentioning $oldUnsupportedVersion. Just for the case that oracle would add a newer version of the Unicode character set in a future major upgrade… In that case this would become relevant again… but if the consensus is to remove the sentence, I can do that…

[dbussink]

I'd say we can drop the entire second sentence? Maybe something like:

Character set or collation name used by this tablet for the connection to MySQL

Just for the case that oracle would add a newer version of the Unicode character set in a future major upgrade…

I doubt this would happen, but they do have 4 chances to do this 😉. See:

SELECT id, COLLATION_NAME FROM INFORMATION_SCHEMA.COLLATIONS order by id;
...
| 249 | gb18030_bin                 |
| 250 | gb18030_unicode_520_ci      |
| 255 | utf8mb4_0900_ai_ci          |
...

Giving this is a one byte field in the MySQL handshake protocol, only 251, 252, 253 & 254 are not used yet. You can't use any of the names with an Id > 255 here anyway because of that limitation.

But I also think that if that time comes, we can further clarify it with the situation that is then current?

[deepthi]

I say let's merge this for now and if and when things change we can revisit.