Add caveat re: CDC nobackfill schema change policy

[rmloveland]

Fixes DOC-15563

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Files changed:

• src/current/v23.2/create-changefeed.md
• src/current/v24.1/create-changefeed.md
• src/current/v24.3/create-changefeed.md
• src/current/v25.1/create-changefeed.md
• src/current/v25.2/create-changefeed.md
• src/current/v25.3/create-changefeed.md
• src/current/v25.4/create-changefeed.md
• src/current/v26.1/create-changefeed.md

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[rmloveland]

@smcvey @fqazi I hope this captures the nuance of which versions of CRDB are effected and under which conditions, please let me know if add'l changes are needed!

[fqazi]

Looks good @rmloveland . We also want similar changes on newer releases.

[rmloveland]

Looks good

thanks @fqazi !

We also want similar changes on newer releases.

oh interesting - the jira issue says "this only applies to versions before v25.1", sounds like that was incorrect?

are you saying we should make this doc update for all of the newer releases as well? (i.e., v25.1, v25.3, v25.4, and v26.1)

[fqazi]

@rmloveland I think it's because auto_commit_before_ddl is enabled by default on those releases. But users can also toggle it off on later releases, which this message covers. @smcvey Do you have any thoughts on this?

[smcvey]

We have had some customers switching off auto_commit_before_ddl after upgrading and discovering it had changed - it was breaking their schema changing tools so I think including it in later versions of the docs should still happen, but mention that only if auto_commit_before_ddl is disabled.

[rmloveland]

We have had some customers switching off auto_commit_before_ddl after upgrading and discovering it had changed - it was breaking their schema changing tools so I think including it in later versions of the docs should still happen, but mention that only if auto_commit_before_ddl is disabled.

ah ok thanks for that info @smcvey ! I have updated the v25.1 and later docs with the following in this commit:

However, if the schema change with column backfill runs inside an [explicit transaction]({% link {{ page.version.version }}/begin-transaction.md %}) and the [autocommit_before_ddl session setting]({% link {{page.version.version}}/set-vars.md %}#autocommit-before-ddl) is disabled, it will emit the entire table to the changefeed.

[rmloveland]

thanks for the helpful comments and reviews, @fqazi and @smcvey - i'm gonna pass this to Docs team for internal review to get merged ASAP

[florence-crl]

lgtm