fixing issue with xtrabackup and long gtids

[rvrangel]

Description

Instead of reading the GTIDs from the xtrabackup output, this will make use of the --extra-lsndir flag to output a copy of the xtrabackup_info file which has the full GTID information, instead of reading it from the STDERR where it eventually gets truncated after the line size gets close to ~8KB

Related Issue(s)

Fixes #16303

Checklist

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Deployment Notes

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[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 68.68%. Comparing base (bb76046) to head (fa9969f).
Report is 48 commits behind head on main.

Files	Patch %	Lines
go/vt/mysqlctl/xtrabackupengine.go	75.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16304      +/-   ##
==========================================
- Coverage   68.71%   68.68%   -0.04%     
==========================================
  Files        1544     1548       +4     
  Lines      198011   199094    +1083     
==========================================
+ Hits       136064   136738     +674     
- Misses      61947    62356     +409     

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[timvaillancourt]

@rvrangel will this flag exist in "most" recent versions of xtrabackup?

[rvrangel]

good question, it is present since the 2.4 EOL version, so any recent version should have it I imagine.

[deepthi]

Where will the temporary directory be created by default? Are we sure to have the necessary permissions?
I'm wondering why not use params.Cnf.TmpDir and just write the file there.

[rvrangel]

it will default to the system's $TMPDIR (usually /tmp) which we should almost always have permissions, the idea was that we could just remove it once we are done. but if we want to create it under params.Cnf.TmpDir, seems like the --target-dir is mostly unused because we stream the backup to STDOUT.

we could also use that path directly and instead of creating the temporary subdirectory and we either delete the files separately (it is just xtrabackup_info and xtrabackup_checkpoints) or we could just leave them there as the result of the last xtrabackup taken. @deepthi do you have a preference?

[deepthi]

What are the pros and cons of leaving the files behind versus deleting them? The next backup would overwrite them anyway, right?
Beyond this one decisions, almost any of the options would work. It's probably a bit simpler to not create a new temporary directory and just use one of the existing ones.

[rvrangel]

leaving them is mostly for investigation (if needed), I guess we can just not remove them so there is a copy in the temp folder of the files from the last backup attempt in case an operator wants to look at it, otherwise it will just get overwritten the next time a backup is taken. I will update the PR tomorrow

[rvrangel]

PR has been updated 🙌

[deepthi]

This will be a good change. The original implementation was definitely somewhat naive :)

[deepthi]

Where will the temporary directory be created by default? Are we sure to have the necessary permissions?
I'm wondering why not use params.Cnf.TmpDir and just write the file there.

[deepthi]

The DCO check needs to be fixed before we can merge this.
The actual changes look good.