feat(mcp-guard): performance_schema.mcp_tool_calls and audit messages (RFC 0001 Phase 3) by askdba · Pull Request #243 · askdba/myvector

askdba · 2026-10-31T08:52:38Z

Phase 3 (server side) of RFC 0001. The Go side, which writes the labels, is askdba/mysql-mcp-server#157.

What

performance_schema.mcp_tool_calls: one row per mysql-mcp-server tool call, built from the MCP session statements that start with /* mcp:tool=<tool> req=<id> */. Columns: CONNECTION_ID, ACCOUNT, TOOL, REQUEST_ID, STATEMENTS, ERRORS, DENIED, LATENCY_US, FIRST_SEEN, LAST_SEEN. It is read-only and in memory, a ring of mcp.tool_calls_history_size calls (new read-only variable, default 1000, 0 = none).
Audit messages: each refusal is emitted with mysql_audit_api_message (MYSQL_AUDIT_MESSAGE_INTERNAL, component mcp_guard, producer component_mcp_guard, message refused). Keys: option, connection_id, statement (redacted like the error log), and tool/request_id for labeled statements.
Labels only attribute statements. MCP sessions are still identified by MCP_USER, so labels from other accounts are ignored. ACCOUNT is the trusted column.
The query consumer now also receives top-level STATUS_END, for latency and errors. A statement refused at its start gets no STATUS_END, so the refusal ends it.
Teardown: the P_S table is removed right after the variables. If that fails, deinit fails and the library stays loaded, as with the variables.

Verification

scripts/test-mcp-guard.sh: 90/90 on MySQL 8.4.11, 9.7.2 and 26.10.0 (10 new checks: row positions, ordered read and self-join, grouping, refusals at statement and table level, latency, unlabeled statements and other accounts ignored, read-only table, gone after uninstall).
The parse_call_label unit tests pass.
Ring wrap-around: with INSTALL COMPONENT … SET GLOBAL mcp.tool_calls_history_size = 3, after 5 calls only r3, r4, r5 are kept. SET GLOBAL is refused (read-only).
Audit messages: checked with a throwaway event_tracking_message consumer component (not committed). A refusal inside a tool call arrived as option=[mcp.read_only] connection_id=12 statement=[/* mcp:tool=run_query req=abc-1 */ INSERT …] tool=[run_query] request_id=[abc-1]. An unlabeled one arrived with its literals redacted (VALUES ('?')).
End to end: the mysql-mcp-server feat(search): filtered ANN search via an allowed-key list #157 binary over stdio with list_tables, describe_table, run_query and server_info produced one row per call, with the right tool, request id, statement count and latency.

🤖 Generated with Claude Code

Summary by CodeRabbit

New Features
- Added a read-only Performance Schema table showing labeled MCP tool calls, including statement and refusal counts, execution time, and timestamps.
- Added configurable history retention, defaulting to 1,000 calls. Set the limit to zero to retain no calls; history is cleared on restart or component reinstall.
- Refused calls now generate audit messages, independent of the denial-logging setting.
Documentation
- Documented the tracking table, history setting, and refusal audit messages.

… (RFC 0001 Phase 3) - performance_schema.mcp_tool_calls: one row per mysql-mcp-server tool call, grouped from MCP session statements labeled /* mcp:tool=... req=... */ (account, tool, request id, statements, errors, refusals, latency, first/last seen), in a ring of mcp.tool_calls_history_size calls (read-only, default 1000). - Each refusal is emitted through mysql_audit_api_message (component mcp_guard, message "refused", with option, connection id, redacted statement, tool call). - Top-level STATUS_END events are now received to measure latency and errors; a statement refused at its start (no STATUS_END) is ended in the refusal. - test-mcp-guard.sh: 89 checks on 8.4.11, 9.7.2, 26.10.0; parse_call_label unit-tested. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

chatgpt-codex-connector · 2026-10-31T08:52:52Z

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-31T08:55:48.604194Z	`9c49ecb`	PR opened

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coderabbitai · 2026-10-31T08:52:55Z

No actionable comments were generated in the recent review.

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Reviewing files that changed from the base of the PR and between 9c49ecb and 10488c4.

Files selected for processing: 4

CHANGELOG.md
docs/MCP_COMPONENTS.md
scripts/test-mcp-guard.sh
src/mcp/guard/component_mcp_guard.cc

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CHANGELOG.md
docs/MCP_COMPONENTS.md

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Walkthrough

The guard parses labeled MCP tool calls, retains call and statement metrics in performance_schema.mcp_tool_calls, and emits audit messages for refusals. The history size is configurable. Documentation and tests cover the table and label behavior.

Changes: MCP guard tracking

Layer / File(s)	Summary
Label parsing and session state `src/mcp/guard/component_mcp_guard.cc`, `src/mcp/guard/mcp_guard_policy.h`, `src/mcp/guard/test_mcp_guard_policy.cc`, `docs/MCP_COMPONENTS.md`	The guard adds the read-only `mcp.tool_calls_history_size` setting and parses labels with tool and request identifiers. Session state stores the active call and account information. Unit tests cover valid and invalid labels.
Call history and Performance Schema table `src/mcp/guard/component_mcp_guard.cc`, `scripts/test-mcp-guard.sh`, `docs/MCP_COMPONENTS.md`, `CHANGELOG.md`	A bounded ring retains call records, which the read-only `performance_schema.mcp_tool_calls` table exposes. Integration checks cover record contents, filtering, read-only behavior, and table removal after uninstall. Documentation describes the setting, table, and test coverage.
Query tracking and refusal auditing `src/mcp/guard/component_mcp_guard.cc`, `docs/MCP_COMPONENTS.md`	Query events update statement counts, errors, and latency for labeled calls. Refusals emit audit messages and update denial counts. Audit messages include tool and request identifiers when a labeled call is active.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant QueryCallback
  participant parse_call_label
  participant CallHistory
  participant mysql_audit_api_message
  QueryCallback->>parse_call_label: Parse the query call label
  parse_call_label-->>QueryCallback: Return tool and request identifiers
  QueryCallback->>CallHistory: Start or update the labeled call record
  QueryCallback->>mysql_audit_api_message: Emit a refusal audit message
  QueryCallback->>CallHistory: Record the refusal for the active call

Possibly related PRs

askdba/myvector#242: Adds refusal handling that this change extends with audit events and per-call denial counts.
askdba/myvector#241: Adds guard enforcement and session state used by labeled statement tracking.
askdba/myvector#238: Adds the procedures whose labeled tool-call statements this change records.

Merge Risk: Minimal · up to 10488

No actionable issue remains identified for this change; it is ready for normal merge checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 29.17% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the primary changes: the new performance_schema.mcp_tool_calls table and audit messages for the MCP guard.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 29.17% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 24 functions across 4 files. (2 skipped: 2 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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_{A rabbit reads each call label with care,
Then keeps bounded records tucked there.
Refusals leave an audit trace,
While counts and timings take their place.
The newest calls stay in the ring,
And silent rows say nothing.}

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chatgpt-codex-connector · 2026-10-31T08:55:46Z

+  return t->pos < t->rows.size() ? 0 : PFS_HA_ERR_END_OF_FILE;
+}
+
+int call_table_rnd_pos(PSI_table_handle *h) { return call_table_rnd_next(h); }


Implement random-position reads for the table

When a query plan needs to revisit a Performance Schema row by saved position, this rnd_pos callback advances to the next row instead of restoring the requested row; open_table also leaves the position buffer unset despite declaring a nonzero reference length. Such reads can return the wrong row or fail. Bind the position buffer and make rnd_pos restore that position.

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Fixed in 10488c4: open_table exposes the handle's current row (pos) as the PSI_pos the server saves and restores, and rnd_pos reads that restored row instead of advancing the scan. This follows pfs_example_continent's pos/next_pos pattern. On the regression test: I couldn't find a plan that makes the server re-read rows by position on this unindexed, read-only table. Filesort uses packed addon fields even at the minimum sort_buffer_size (checked with the optimizer trace), and the plans that use row positions (multi-table UPDATE/DELETE) can't run on a read-only P_S table. The test now covers an ordered read and a self-join, which opens two handles (90 checks on 8.4.11, 9.7.2, 26.10.0).

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Inline comments:
Review comments at @src/mcp/guard/component_mcp_guard.cc:
- Line 503: Update call_table_open to expose the handle’s position through
PSI_pos ** so the server can save and restore it, then update call_table_rnd_pos
to use that restored position rather than advancing the scan cursor. Add a
regression test that exercises row-position access, such as sorting by row ID.

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CHANGELOG.md
docs/MCP_COMPONENTS.md
scripts/test-mcp-guard.sh
src/mcp/guard/component_mcp_guard.cc
src/mcp/guard/mcp_guard_policy.h
src/mcp/guard/test_mcp_guard_policy.cc

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open_table exposes the handle's current row as the PSI_pos the server saves and restores, and rnd_pos reads the restored row instead of advancing the scan (pos/next_pos as in pfs_example_continent). Review of #243. test-mcp-guard.sh: ordered read and self-join of mcp_tool_calls (90 checks). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

askdba · 2026-10-31T14:56:28Z

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askdba · 2026-10-31T14:57:13Z

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askdba · 2026-10-31T15:47:47Z

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coderabbitai · 2026-10-31T15:47:53Z

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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

chatgpt-codex-connector Bot reviewed Oct 31, 2026

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Comment thread src/mcp/guard/component_mcp_guard.cc Resolved

askdba mentioned this pull request Oct 31, 2026

feat(docker): mysql-mcp images with component_mcp_guard and the tool pack (RFC 0001 Phase 3) #244

Merged

askdba mentioned this pull request Oct 31, 2026

docs(rfc): RFC 0001 plan status (Phases 1-3 done); record Q6 askdba/mysql-mcp-server#158

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askdba merged commit 21758c8 into main Oct 31, 2026
37 checks passed

askdba deleted the feat/mcp-tool-calls branch October 31, 2026 15:53

askdba added a commit to askdba/mysql-mcp-server that referenced this pull request Oct 31, 2026

docs(rfc): mark Phase 3 done (#157, askdba/myvector#243, #244, #245)

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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

askdba mentioned this pull request Oct 31, 2026

Post-merge review of #244, #245, #246, #248 (do not merge) #249

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