balance: lower the OOM risk level during TiDB bootstrap

[djshow832]

What problem does this PR solve?

Issue Number: close #848

Problem Summary:
When TiDB starts, the memory usually increases sharply, leading to fake OOM risk. This will cause unnecessary session migrations.

What is changed and how it works:
Adjust the TimeToOOM to timeToOOM = time.Duration(float64(timeToOOM) / latestUsage * 0.6).

• /latestUsage: the lower the current usage is, the longer the timeToOOM is
• * 0.6: lower the timeToOOM so that the thresholds don't need to be changed

Check List

Tests

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

Notable changes

• Has configuration change
• Has HTTP API interfaces change
• Has tiproxyctl change
• Other user behavior changes

Release note

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

None

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@99915da). Learn more about missing BASE report.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1167   +/-   ##
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  Coverage        ?   67.60%           
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  Files           ?      150           
  Lines           ?    16661           
  Branches        ?        0           
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  Hits            ?    11264           
  Misses          ?     4636           
  Partials        ?      761           

Flag	Coverage Δ
unit	67.60% <100.00%> (?)

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[YangKeao]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: YangKeao

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Details

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• OWNERS [YangKeao]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-06-04 07:58:22.831169448 +0000 UTC m=+428403.901486828: ☑️ agreed by YangKeao.

[djshow832]

/cherry-pick release-1.3

[ti-chi-bot]

@djshow832: new pull request created to branch release-1.3: #1168.

Details

In response to this:

/cherry-pick release-1.3

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[djshow832]

/cherry-pick release-nextgen-202603

[ti-chi-bot]

@djshow832: new pull request created to branch release-nextgen-202603: #1169.

Details

In response to this:

/cherry-pick release-nextgen-202603

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.