server: limit the size for COM_STMT_SEND_LONG_DATA in each connection

[djshow832]

What problem does this PR solve?

Issue Number: close #70349

Problem Summary:
#69693 only limits the size of a single COM_STMT_SEND_LONG_DATA, but it does limit the size for each statement, connection, user, or instance.

What changed and how does it work?

• Attach the param memory to the session memory tracker.
• If the session memory exceeds the quota, do not append the param and report an error in the ComExecute.
• Release the memory after the statement closes or resets.

Note that it only limits memory on the connection level, not the user or instance level, but it's enough for most cases.

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

Summary by CodeRabbit

• Bug Fixes
  • Prepared statements now correctly enforce query memory quotas for long-data parameters.
  • Additional data is rejected when memory or packet limits are reached.
  • Memory used by long-data parameters is released after execution failures and when statements are reset or closed.
  • Subsequent statements can reuse released memory without retaining stale parameter data.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 16ef83db-daa3-40a2-918e-038c08f23dbc

📥 Commits

Reviewing files that changed from the base of the PR and between 04c65cb and 1398da1.

📒 Files selected for processing (1)

• pkg/server/driver_tidb.go

🚧 Files skipped from review as they are similar to previous changes (1)

• pkg/server/driver_tidb.go

---

📝 Walkthrough

Walkthrough

COM_STMT_SEND_LONG_DATA now enforces query memory quotas, tracks accepted bytes, reports quota errors, and releases tracked memory during statement reset or close. Tests cover quota refusal, recovery, and cleanup.

Changes

Long-data quota enforcement

Layer / File(s)	Summary
Quota tracking and statement cleanup pkg/server/driver_tidb.go	TiDBStatement tracks charged long-data bytes, enforces max_allowed_packet and query memory limits, reports quota errors, and releases state during reset and close.
Quota behavior validation pkg/server/conn_stmt_test.go	Tests verify quota enforcement, rejected excess data, execution errors, later accepted data, and memory release on statement close.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• pingcap/tidb#69694: Extends related COM_STMT_SEND_LONG_DATA size enforcement.
• pingcap/tidb#70083: Modifies the same long-data handling and cleanup logic.
• pingcap/tidb#70170: Updates TiDBStatement long-data validation.

Suggested reviewers: bb7133, yangkeao, tiancaiamao

Poem

A rabbit tracks each long-data byte,
Then stops at the quota gate.
Cleanup frees the stored amount,
Reset clears the statement state.
Hop, hop—the next query starts.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the connection-level size limit added for COM_STMT_SEND_LONG_DATA.
Description check	✅ Passed	The description includes the issue, problem, implementation details, unit test coverage, side effects, documentation checks, and release note.
Linked Issues check	✅ Passed	The changes address issue #70349 by bounding connection-level long-data memory, reporting quota errors, and releasing memory on reset or close.
Out of Scope Changes check	✅ Passed	The changes remain focused on COM_STMT_SEND_LONG_DATA limits, memory tracking, error handling, cleanup, and related unit tests.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@pkg/server/driver_tidb.go`:
- Line 121: Update the empty-data branch in the relevant long-data handling
method before its return to release the replaced parameter’s boundLongDataBytes
charge and corresponding session MemTracker charge, preserving normal behavior
for non-empty data. Add a regression test covering an initial data chunk
followed by an empty chunk for the same parameter and verify the tracker charge
is released.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 5c91b6cb-dd77-45e6-bc71-32bffb410b90

📥 Commits

Reviewing files that changed from the base of the PR and between ea373a0 and b7810b1.

📒 Files selected for processing (2)

• pkg/server/conn_stmt_test.go
• pkg/server/driver_tidb.go

[codecov]

Codecov Report

❌ Patch coverage is 0% with 42 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.4252%. Comparing base (8380b57) to head (1398da1).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #70350        +/-   ##
================================================
- Coverage   76.3271%   73.4252%   -2.9020%     
================================================
  Files          2041       2078        +37     
  Lines        559032     583952     +24920     
================================================
+ Hits         426693     428768      +2075     
- Misses       131439     154708     +23269     
+ Partials        900        476       -424     

Flag	Coverage Δ
integration	40.7336% <0.0000%> (+1.0650%)	⬆️

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

Components	Coverage Δ
dumpling	59.9240% <ø> (ø)
parser	∅ <ø> (∅)
br	46.6167% <ø> (-16.0923%)	⬇️

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