Wave 1 follow-up: dir-fsync boot regression, TXN FLUSHDB/FLUSHALL refusal, CHANGELOG accuracy

[TinDang97]

Summary

This PR applies the fixes from the fourth adversarial review round of PR #1301. #1301 had already merged by the time the round finished.

• moon#1293: boot regression from Wave 1 (2026-09 round): durable TXN.ABORT, no-AOF tiering and graves residuals, eviction/expiry/SSCAN performance #1301 (c55924b).
  • Symptom: on a filesystem that cannot fsync directories (vboxsf, WSL1 drvfs), --dir /mnt/x/moon/data with two missing levels failed to boot with EINVAL.
  • Fix: such errors are now skipped on created and pre-existing directories alike. They are matched on the raw errno: EINVAL, EROFS, EBADF, ENOTSUP, EOPNOTSUPP, ENOTTY, or ErrorKind::Unsupported. Each call logs one warning. EACCES is tolerated only on a pre-existing ancestor, and EIO stays fatal.
  • resolve_dir: a user-data directory that exists but could not be made durable is now kept, instead of silently falling back to ..
• moon#1285: FLUSHDB / FLUSHALL inside a TXN (pre-existing data loss).
  • Symptom: these commands ran on the connection inside a TXN, and TXN ABORT answered +OK with the data gone.
  • Fix: both runtimes now refuse them before routing with ERR TXN cannot roll back this command (whole-database write) -- run it outside the TXN. The refusal also poisons the TXN, so COMMIT answers EXECABORT. The script path already refused them; both paths now share one list (transaction::TXN_WHOLE_DB_WRITES).
• Docs:
  • The CHANGELOG no longer claims that a write-flagged command that only reads its keys "captures nothing" in every case. It names the remaining over-capture cases, which are tracked in moon#1299 and moon#1303.
  • A misplaced doc comment is restored.
  • The WS31 SUMMARY gains its round-4 section.

Checklist

All of these ran on head 267b518 in a Linux container (4 vCPU x86_64), not the merge bar:

• cargo fmt --check passes.
• cargo clippy --all-targets -- -D warnings passes on monoio and on runtime-tokio,jemalloc. cargo check --manifest-path fuzz/Cargo.toml --all-targets passes.
• cargo test --all-features: not run (gpu-cuda can't run here). What ran instead:
  • cargo test --release --lib passed on both runtimes.
  • 58 integration legs ran with --include-ignored and MOON_BIN pinned to a release binary of each runtime. 56 are green, including txn_abort_durability_1285 at 25/25 on each runtime.
  • The 2 red legs contain only the 3 known tokio replica tests (script_move_copy_db_replica_agrees_{1,4}_shard_master, script_effects_in_exec_reach_the_replica_in_order). Tokio has no master-side PSYNC, and they fail the same way on base.
• Consistency tests: not re-run for this follow-up. It does not touch any command's reply on the non-TXN path.

Red → green:

• FLUSHDB/FLUSHALL: connection_writes_the_txn_cannot_undo_are_refused_shards_{1,4} fails on the Wave 1 (2026-09 round): durable TXN.ABORT, no-AOF tiering and graves residuals, eviction/expiry/SSCAN performance #1301 head binaries and passes here, on both runtimes and after kill -9.
• Directory fsync: unit tests dir_fsync_error_classification, create_dir_all_durable_skips_unsupported_dir_fsync_on_created_dirs, create_dir_all_durable_keeps_eio_and_created_dir_eacces_fatal and test_user_data_dir_choice. The previous code's own test asserted that EINVAL on a created directory was fatal.

Not run: the moon-dev VM and macOS, where the errno values for ENOTSUP and EOPNOTSUPP differ from Linux and are untested; Windows; crash-matrix.yml.

Performance Impact

None.

• TXN check: one set lookup on the TXN write path, only while a TXN is open.
• Directory fsync: runs at boot and at AOF generation creation.

Notes

• Behaviour change: inside a TXN, FLUSHDB / FLUSHALL (plain, ASYNC or SYNC) now answer an error and poison the TXN.

• Residuals, tracked in moon#1299 / moon#1303:

  • LMPOP/ZMPOP capture every candidate key;
  • a connection write that answers an error keeps its capture;
  • successful no-op writes (SETNX on an existing key, SET … NX, COPY without REPLACE, RENAMENX, LPUSHX on a missing key, SMOVE of a missing member) keep their capture;
  • GEORADIUSBYMEMBER g STORE 100 km and XGROUP HELP <x> capture a key they never write.

  Blocking other writers on keys held by an open TXN (moon#1299) makes all of these harmless.

• SWAPDB, MOVE and COPY … DB inside a TXN still answer the older ERR_TXN_CROSS_SHARD text. That text predates this PR and is unchanged here.

🤖 Generated with Claude Code

https://claude.ai/code/session_01D81NZwUjEnWCaZekSCB3Uu

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Generated by Claude Code

Summary by CodeRabbit

• Bug Fixes
  • FLUSHDB and FLUSHALL issued on a connection during an open transaction are now refused before execution. The transaction is marked for abort, so COMMIT returns an error and accepted changes are rolled back.
  • Startup now continues when directory syncing is unsupported, with a warning. Inaccessible existing parent directories are skipped; other serious errors, including I/O errors, remain fatal.
  • When the configured user-data directory exists but cannot be made durable, the server uses it with a warning instead of falling back to the current directory.
• Documentation
  • Clarified transaction key-capture and directory-sync behavior.

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Review configuration:

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: d5fd74be-a649-4853-b52a-531fef9a6f81

📥 Commits

Reviewing files that changed from the base of the PR and between 267b518 and e90638e.

📒 Files selected for processing (4)

• CHANGELOG.md
• src/config.rs
• src/main.rs
• src/server/embedded.rs

📝 Walkthrough

Walkthrough

The pull request changes directory-fsync error handling and user-data directory selection. It also adds transaction guards for whole-database writes in both connection handlers, with tests for refusal and transaction abort behavior.

Changes

Directory durability

Layer / File(s)	Summary
Directory fsync error handling src/persistence/fsync.rs, CHANGELOG.md, .add/milestones/v0-9-2-perf-review/plans/WS31-txn-abort-review-fixes/SUMMARY.md	Unsupported fsync errors are tolerated for created and pre-existing directories. Permission errors remain tolerable only for pre-existing directories. Skipped fsyncs for new entries produce one warning per call.
User-data directory selection src/config.rs	resolve_dir retains an existing user-data directory after a durability error and falls back to the current directory if that directory is absent. Tests cover all three selection outcomes.

Transaction write refusal

Layer / File(s)	Summary
Whole-database write classification and error contract src/transaction/mod.rs, src/command/transaction.rs, src/scripting/bridge/txn_capture.rs, src/tracking/invalidation.rs, CHANGELOG.md	The transaction module defines the whole-database write commands and a case-insensitive predicate. The public error documents refusal and transaction poisoning. The capture reference and changelog are updated.
Connection guards and abort verification src/server/conn/handler_monoio/mod.rs, src/server/conn/handler_sharded/mod.rs, tests/txn_abort_durability_1285.rs, CHANGELOG.md	Both handlers refuse selected commands during an active transaction without executing them. Integration tests check that the refusal poisons the transaction and that commit aborts accepted writes.

Priority: ➖ Normal

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

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant ConnectionHandler
  participant Transaction
  Client->>ConnectionHandler: Send FLUSHDB or FLUSHALL during TXN
  ConnectionHandler->>Transaction: Mark rejected
  ConnectionHandler-->>Client: Return ERR_TXN_NOT_UNDOABLE
  Client->>ConnectionHandler: Commit transaction
  ConnectionHandler->>Transaction: Process commit
  Transaction-->>Client: Return EXECABORT

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Suggested reviewers: claude

Merge Risk: 🟡 Moderate · up to 267b5

Startup can continue after a fatal directory-durability failure. Preserve propagation of these errors before merging; the transaction refusal changes have no established remaining defect.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to 267b5

The transaction changes strengthen rollback protection and the directory changes avoid silently moving data elsewhere. However, startup can retain a directory after a durability failure without completing every required ancestor flush, potentially leaving stored data unreachable after power loss.

Retained concerns

• Medium · reliability · inferred: Retaining a partially durable user-data tree loses the original creation provenance across startup validation. With multiple missing directory levels, a fatal fsync failure can leave ancestor entries unsynced; the next validation sees an existing tree and does not retry every original ancestor. Startup can therefore use the tree despite an incomplete durability operation, placing persistence recovery at risk after power loss. The previous selection behavior did not use that failed tree during the same startup.

Security review details

Security Blast Radius

• inferred — The recovery concern is bounded to persistence beneath the affected auto-selected directory tree. Loss of an ancestor entry can make that tree unreachable, potentially affecting the instance's stored data rather than only one transaction or key. No new cross-service exposure is established by this failure path.

Security Findings and Attack Paths

• inferred — The identified path requires nested directory creation and a fatal fsync failure, followed by retained-path selection and incomplete ancestor retry. A later power loss may expose the recovery-integrity failure. This is not a demonstrated remote exploit or privilege escalation.

Trust Boundaries and Controls

• observed — The refusal control is tied to the client's active connection transaction. Normal binary startup also acquires an exclusive data-directory lock before opening persistence files or binding listeners; that lock prevents a second writer but does not flush missing ancestor entries.

Resilience and Maintainability Implications

• observed — The added transaction integration case asserts refusal, rollback after dirty COMMIT, preservation of another logical database, outside-TXN behavior, and restart state for one and four shards. These are source-level test assertions; this review did not execute them.

Hardening Proposals

• proposed — Preserve fatal-error and created-ancestor provenance across directory selection and validation. Recovery should complete every required ancestor flush or refuse startup, without silently moving data to the working directory. Fault-inject the complete selection-to-validation sequence to verify this invariant.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description includes all required sections. It summarizes the changes, reports checklist results and test limitations, states the performance impact, and documents relevant behavior changes and fo…
Title check	✅ Passed	The title clearly identifies the three main changes: the directory-fsync boot fix, TXN refusal for FLUSHDB/FLUSHALL, and CHANGELOG updates.
Docstring Coverage	✅ Passed	Docstring coverage is 89.66% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 29 functions across 9 files. (2 skipped: 2 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @src/config.rs:
- Line 1085: Update user_data_dir_choice in resolve_dir to propagate
non-tolerated durability errors from create_dir_all_durable, including EIO, even
when the target directory already exists; reserve UseDespite for errors that are
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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: b13611f0-b8f9-4528-aba2-3f86ead36434

📥 Commits

Reviewing files that changed from the base of the PR and between 9d72003 and 267b518.

📒 Files selected for processing (11)

• .add/milestones/v0-9-2-perf-review/plans/WS31-txn-abort-review-fixes/SUMMARY.md
• CHANGELOG.md
• src/command/transaction.rs
• src/config.rs
• src/persistence/fsync.rs
• src/scripting/bridge/txn_capture.rs
• src/server/conn/handler_monoio/mod.rs
• src/server/conn/handler_sharded/mod.rs
• src/tracking/invalidation.rs
• src/transaction/mod.rs
• tests/txn_abort_durability_1285.rs

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