memory, config: reject connections when memory usage is high (#1120)

[ti-chi-bot]

This is an automated cherry-pick of #1120

What problem does this PR solve?

Issue Number: close #1119

Problem Summary:
TiProxy may OOM when the connection count is too large

What is changed and how it works:

• Reject new connections when memory usage is too high
• Report unhealthy on the status port when the memory usage is too high

Check List

Tests

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

The memory usage and connection count increased to a fixed value:

The server shows connections are rejected:

The client failed to connect anymore:

After restarting the client, the client can connect again

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.

- Reject connections and report unhealthy when the memory usage is too high

[ti-chi-bot]

@djshow832 This PR has conflicts, I have hold it.
Please resolve them or ask others to resolve them, then comment /unhold to remove the hold label.

[djshow832]

/unhold

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: djshow832

The full list of commands accepted by this bot can be found here.

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Details

Needs approval from an approver in each of these files:

• OWNERS [djshow832]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-04-22 12:10:34.628716201 +0000 UTC m=+2167839.834076258: ☑️ agreed by djshow832.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 76.71233% with 34 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-1.3@ed859d5). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
pkg/manager/memory/memory.go	67.77%	19 Missing and 10 partials ⚠️
pkg/proxy/net/packetio.go	0.00%	2 Missing and 1 partial ⚠️
pkg/proxy/proxy.go	95.45%	2 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff               @@
##             release-1.3    #1136   +/-   ##
==============================================
  Coverage               ?   65.61%           
==============================================
  Files                  ?      124           
  Lines                  ?    12165           
  Branches               ?        0           
==============================================
  Hits                   ?     7982           
  Misses                 ?     3641           
  Partials               ?      542           

Flag	Coverage Δ
unit	65.61% <76.71%> (?)

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