*: always convert sysvar values when out of range

[morgo]

What problem does this PR solve?

Issue Number: close #25397

Problem Summary:

In MySQL sysvars that are of the correct type but out of range return a warning and not an error.

Previously TiDB returned an error unless AutoConvertOutOfRange = true. Now AutoConvertOutOfRange = true is permanently set, and the field has become meaningless and removed.

The error that TiDB returned was also not helpful (incorrect argument type).

What is changed and how it works?

What's Changed:

When setting a system variable, TiDB now attempts to convert out of range values to the closest approximate value. For example, a value of 501 might be adjusted to the maximum value of 500. This behavior is more compatible with how MySQL accepts system variable values.

Related changes

• None (not suitable for cherry pick)

Check List

Tests

• Unit test

Side effects

• Behavior change (but less strict, so unlikely to cause compatibility issues).

Release note

• When setting a system variable, TiDB now attempts to convert out of range values to the closest approximate value. For example, a value of 501 might be adjusted to the maximum value of 500. This behavior is more compatible with how MySQL accepts system variable values.

[xhebox]

Rest LGTM
But should we consider this PR a compatibility breaker? Not every variable is autoconvert=true before, right?

[morgo]

Rest LGTM
But should we consider this PR a compatibility breaker? Not every variable is autoconvert=true before, right?

I actually don't think it is compatibility breaking since it changes the server to be less strict (versus more strict; which usually is an issue). But it is easy to ague either way.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• dveeden
• xhebox

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[bb7133]

/merge

[ti-chi-bot]

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[morgo]

/merge cancel

Needs approval first or it will block other merges

[morgo]

/run-check_dev_2

[bb7133]

It doesn't 'break' the compatibility but may lead to some changed behaviors(though the chance is little). I tagged 'compatibility breaker' so that it will be noticed.

[bb7133]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: e600b6c