stmtsummary: fix a memory leak caused by stmt summary referencing packet data

[tiancaiamao]

What problem does this PR solve?

Issue Number: ref #64256

Problem Summary:

Maybe they are the same leak, but maybe not.

From the Go heap profile, I can see the packet data memory is leak

And using goref https://github.com/cloudwego/goref, stmtsummary is the root refercing data:

What changed and how does it work?

Key path (from packet allocation to being held by stmt summary):

• pkg/server/internal/packetio.go:178-190
  data := make([]byte, length) allocates the full packet payload.
• pkg/server/conn.go:1400
  dataStr := string(hack.String(data)) uses unsafe zero-copy to convert []byte to string.
• pkg/parser/lexer.go:107
  stmtText() takes a substring of the original SQL: text := s.r.s[s.stmtStartPos:endPos], without copying.
• pkg/parser/ast/base.go:52
  The AST node stores text (still referencing the original underlying array).
• pkg/executor/select.go:1047
  sc.OriginalSQL = s.Text() puts the AST text into StmtCtx.OriginalSQL.
• pkg/util/stmtsummary/statement_summary.go:660
  sampleSQL: formatSQL(sei.LazyInfo.GetOriginalSQL())
• pkg/util/stmtsummary/statement_summary.go:942
  formatSQL returns the original string directly when length <= tidb_stmt_summary_max_sql_length.

Result:

stmt summary keeps the original SQL string, and that string actually points to the packet’s underlying buffer.
For multi-statement or large SQL, even if a single statement is short, the substring still keeps the entire packet alive.

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

[tiprow]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.5191%. Comparing base (c2202e1) to head (2926ec9).
⚠️ Report is 15 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #65977        +/-   ##
================================================
- Coverage   77.7795%   77.5191%   -0.2605%     
================================================
  Files          2001       1923        -78     
  Lines        545624     536043      -9581     
================================================
- Hits         424384     415536      -8848     
- Misses       119578     120496       +918     
+ Partials       1662         11      -1651     

Flag	Coverage Δ
integration	41.6406% <50.0000%> (-6.5192%)	⬇️
unit	76.7034% <100.0000%> (+0.2916%)	⬆️

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Components	Coverage Δ
dumpling	56.7974% <ø> (ø)
parser	∅ <ø> (∅)
br	48.8835% <ø> (-12.1072%)	⬇️

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[tiancaiamao]

/retest

[tiprow]

@tiancaiamao: PRs from untrusted users cannot be marked as trusted with /ok-to-test in this repo meaning untrusted PR authors can never trigger tests themselves. Collaborators can still trigger tests on the PR using /test.

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In response to this:

/retest

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[YangKeao]

LGTM 😆

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: xhebox, YangKeao

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-02-03 09:06:37.844683742 +0000 UTC m=+171468.946082461: ☑️ agreed by xhebox.
• 2026-02-03 09:08:25.19805292 +0000 UTC m=+171576.299451635: ☑️ agreed by YangKeao.