session: change the variable range of circuit breaker

[rleungx]

What problem does this PR solve?

Issue Number: close #61614

Problem Summary:

What changed and how does it work?

mysql> show variables like 'tidb_cb_pd%';
+----------------------------------------------+-------+
| Variable_name                                | Value |
+----------------------------------------------+-------+
| tidb_cb_pd_metadata_error_rate_threshold_pct | 0     |
+----------------------------------------------+-------+
1 row in set (0.00 sec)

mysql> set global tidb_cb_pd_metadata_error_rate_threshold_pct = 100;
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> show warnings;
+---------+------+-------------------------------------------------------------------------------+
| Level   | Code | Message                                                                       |
+---------+------+-------------------------------------------------------------------------------+
| Warning | 1292 | Truncated incorrect tidb_cb_pd_metadata_error_rate_threshold_pct value: '100' |
+---------+------+-------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show variables like 'tidb_cb_pd%';
+----------------------------------------------+-------+
| Variable_name                                | Value |
+----------------------------------------------+-------+
| tidb_cb_pd_metadata_error_rate_threshold_pct | 1     |
+----------------------------------------------+-------+
1 row in set (0.00 sec)

mysql> set global tidb_cb_pd_metadata_error_rate_threshold_pct = -1;
Query OK, 0 rows affected, 1 warning (0.01 sec)

mysql> show warnings;
+---------+------+------------------------------------------------------------------------------+
| Level   | Code | Message                                                                      |
+---------+------+------------------------------------------------------------------------------+
| Warning | 1292 | Truncated incorrect tidb_cb_pd_metadata_error_rate_threshold_pct value: '-1' |
+---------+------+------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> show variables like 'tidb_cb_pd%';
+----------------------------------------------+-------+
| Variable_name                                | Value |
+----------------------------------------------+-------+
| tidb_cb_pd_metadata_error_rate_threshold_pct | 0     |
+----------------------------------------------+-------+
1 row in set (0.01 sec)

mysql> set global tidb_cb_pd_metadata_error_rate_threshold_pct = 0.8;
Query OK, 0 rows affected (0.01 sec)

mysql> show variables like 'tidb_cb_pd%';
+----------------------------------------------+-------+
| Variable_name                                | Value |
+----------------------------------------------+-------+
| tidb_cb_pd_metadata_error_rate_threshold_pct | 0.8   |
+----------------------------------------------+-------+
1 row in set (0.00 sec)

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[rleungx]

/cc @benmeadowcroft

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[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 73.6626%. Comparing base (51f0587) to head (26f3bc6).
Report is 5 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #61613        +/-   ##
================================================
+ Coverage   73.1154%   73.6626%   +0.5472%     
================================================
  Files          1729       1729                
  Lines        481057     482505      +1448     
================================================
+ Hits         351727     355426      +3699     
+ Misses       107801     105603      -2198     
+ Partials      21529      21476        -53     

Flag	Coverage Δ
integration	42.5780% <66.6666%> (?)
unit	72.5369% <66.6666%> (+0.1710%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.7804% <ø> (ø)
parser	∅ <ø> (∅)
br	47.1684% <ø> (+0.1792%)	⬆️

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-06-10 06:14:38.158227527 +0000 UTC m=+335656.386542787: ☑️ agreed by tangenta.
• 2025-06-10 06:47:38.839808038 +0000 UTC m=+337637.068123301: ☑️ agreed by okJiang.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: benmeadowcroft, okJiang, tangenta

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Details

Needs approval from an approver in each of these files:

• OWNERS [okJiang,tangenta]
• pkg/sessionctx/vardef/OWNERS [benmeadowcroft]
• pkg/sessionctx/variable/OWNERS [benmeadowcroft]

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[yudongusa]

Please also open a document PR.

[rleungx]

@yudongusa We already had one pingcap/docs#20129