s3keys: add the chunkblob refcount and GC-queue keyspaces - #1225
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First slice of the §3.5 blob GC design: the two Raft-replicated keyspaces the reference-counted grace-period scheme is built on. !s3|chunkref-rc|<sha> -> uint64 reference count !s3|chunkblob-gc-queue|<commitTS>|<sha> -> empty The queue carries its timestamp in the KEY, not the value, because a counter resting at zero records that a blob became reclaimable but not when — which makes the documented grace window unimplementable. The timestamp is fixed-width big-endian so the queue sorts by eligibility time and one range scan finds everything past the boundary; a decimal encoding would order 9 after 10 and silently return the wrong set. ChunkBlobGCQueueScanEnd is exclusive: callers pass now-grace, so an entry stamped exactly at the boundary has not yet served the full window and is excluded. A malformed reference count fails to decode rather than reading as zero. Zero means "no live reference", so defaulting to it on corruption would make a live blob look collectable. Includes an ordering test against the existing chunkblob keyspace: '-' sorts below '|', so !s3|chunkblob-gc-queue| lands entirely BELOW !s3|chunkblob| rather than inside it, and neither range scan can reach the other's keys. Claude-Session: https://claude.ai/code/session_013rNHooj7NF3giihWVba8QE
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📝 WalkthroughWalkthroughチャンク参照カウントキーとGCキューキーのコーデックを追加しました。固定幅のビッグエンディアン時刻でキュー順序と排他的な走査境界を定義しました。不正値の拒否、既存キー空間との分離、関連する設計文書を更新しました。 ChangesチャンクBlob GCキー空間
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to This adds tested GC key codecs without activating runtime GC behavior. The remaining risk is limited to the milestone documentation table rendering incorrectly and obscuring status text. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Full details: Docstring CoverageExplanation Docstring coverage is 76.19% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 21 functions across 2 files. (1 skipped: 1 unsupported.) ✨ Finishing Touches 💡 1📝 Generate docstrings 💡
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Claude finished @bootjp's task in 3m 1s —— View job Claude finished the review
SummaryThis is a clean, well-scoped codec-only PR. I read 1. The
The first clause states an invariant ("must sort below every hex digit") that the second clause immediately contradicts (0x7C is above every hex digit 2. Asymmetric ordering-trap test coverage. The PR explicitly calls out and pins ( 3. Doc vs. code scan-end shape (non-issue, just noting for future readers): §3.5 of the design doc describes the boundary as Note on verificationI was not able to run |
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In `@docs/design/2026_04_25_partial_s3_raft_blob_offload.md`:
- Line 636: Escape each literal pipe character in the keyspace strings within
the M3 Markdown table row as \|, including pipes inside inline-code spans, so
the row remains correctly parsed as three table columns.
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docs/design/2026_04_25_partial_s3_raft_blob_offload.mdinternal/s3keys/chunkblob_gc.gointernal/s3keys/chunkblob_gc_test.go
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| func EncodeChunkRefRC(count uint64) []byte { | ||
| out := make([]byte, u64Bytes) | ||
| binary.BigEndian.PutUint64(out, count) | ||
| return out |
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When a SHA is re-referenced after its count reached zero, the transaction must remove the existing GC-queue entry, but this encoding preserves only the count while ChunkBlobGCQueueKey places the unknown prior timestamp before the SHA. Consequently, the exact queue key cannot be derived from the RC lookup without scanning the entire time-ordered queue. Skipping that expensive scan leaves a stale entry that can become eligible during a later RC-zero interval and delete the blob before the new grace period has elapsed; retain the zero-since timestamp in the RC value or add a SHA-indexed reverse lookup.
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The queue key embeds the eligibility timestamp, so a txn that re-references a SHA after its count reached zero had no way to name the queue entry it must delete atomically with the increment. Nothing in the count value told it when the entry was created. A stale entry left behind would point the sweeper at a blob that is live again. ChunkRefRC now carries QueuedAtNanos alongside the count, so the re-referencing txn can reconstruct the exact key. Queued() reports whether an entry exists at all. Also escapes the pipes in the design doc's milestone table; unescaped "|" inside inline code split the row into seven columns and hid the status text. Claude-Session: https://claude.ai/code/session_013rNHooj7NF3giihWVba8QE
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The re-reference path was unimplementable as designed. Correct: §3.5 requires a txn that re-references a SHA to delete its GC-queue entry atomically with incrementing the count — but the queue key embeds the eligibility timestamp, and nothing in the count value told that txn when the entry was created. It could not name the key it had to delete, so a stale entry would survive and point the sweeper at a blob that is live again.
Markdown table — also correct, and my error: unescaped Revert-checked, restore byte-exact: dropping
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| func ChunkBlobGCQueueScanEnd(boundaryNanos uint64) []byte { | ||
| out := make([]byte, 0, len(ChunkBlobGCQueuePrefix)+u64Bytes) | ||
| out = append(out, chunkBlobGCQueuePrefixBytes...) | ||
| return binary.BigEndian.AppendUint64(out, boundaryNanos) |
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commitTS is not a Unix-nanosecond value: kv/hlc.go encodes it as (UnixMilli << 16) | logical, while this API names the scan boundary boundaryNanos and instructs the sweeper to pass now - gracePeriod. If the forthcoming sweeper follows that contract and supplies time.Now().UnixNano()-grace, every HLC-stamped queue key will sort below the much larger boundary, so newly queued blobs become eligible immediately instead of receiving the grace period. Accept an HLC boundary (and name it accordingly), or provide a helper that converts the wall-clock cutoff into the repository's HLC representation.
AGENTS.md reference: AGENTS.md:L33-L35
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| func ChunkBlobGCQueueKey(commitTSNanos uint64, contentSHA256 [chunkBlobSHA256Bytes]byte) []byte { | ||
| out := make([]byte, 0, | ||
| len(ChunkBlobGCQueuePrefix)+u64Bytes+1+chunkBlobSHA256HexBytes) | ||
| out = append(out, chunkBlobGCQueuePrefixBytes...) | ||
| out = binary.BigEndian.AppendUint64(out, commitTSNanos) |
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When txn-side RC maintenance is added through kv.Coordinator.Dispatch, the mutation keys must be constructed before dispatch, but the authoritative commit timestamp is allocated later inside dispatchTxn; the existing CommitTSValueOffset mechanism can stamp QueuedAtNanos in the RC value but cannot stamp these key bytes. Consequently the required zero-transition transaction cannot atomically create both ChunkBlobGCQueueKey(commitTS, sha) and an RC value carrying that same commit timestamp without obtaining a persistence timestamp outside the coordinator, which is not valid for follower-routed or Phase-D/TSO-backed requests. Add commit-timestamp key patching or base both records on another leader-issued timestamp that is known before the mutation set is built.
AGENTS.md reference: AGENTS.md:L33-L35
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| // Queued reports whether this SHA currently has a GC-queue entry. | ||
| func (r ChunkRefRC) Queued() bool { return r.QueuedAtNanos != 0 } |
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The fresh evidence after the prior re-reference fix is that Queued() now uses zero as the absence sentinel while ChunkBlobGCQueueKey(0, sha) remains accepted and TestChunkBlobGCQueueScanStartCoversTheWholeQueue explicitly treats timestamp zero as a valid queue entry. For such a record, a re-reference sees Queued() == false and cannot remove the old entry; if that SHA later drops to zero again, the already-eligible stale entry can make the sweeper delete it before the new grace period expires. Either reject/reserve timestamp zero throughout the queue API or encode queue presence independently of the timestamp.
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What
First slice of M3 in
docs/design/2026_04_25_partial_s3_raft_blob_offload.md— the two Raft-replicated keyspaces §3.5's reference-counted, grace-period blob GC is built on.Codecs only. The txn-side RC maintenance, the node-local sweeper, and the orphan scan follow in later PRs; this is the substrate they share, so it lands and gets reviewed on its own.
Decisions worth reviewing
The timestamp lives in the key, not the value. §3.5's reasoning, restated because it drives the whole encoding: a counter resting at zero records that a blob became reclaimable but not when, so the documented grace window would be unimplementable. Putting the commit timestamp in the key name makes "became eligible at T" a first-class, sortable fact.
Fixed-width big-endian, not decimal. The queue must sort by eligibility time so a sweeper finds everything past the grace boundary with one range scan. A decimal encoding orders
9after10and silently returns the wrong set — revert-checked.ChunkBlobGCQueueScanEndis exclusive. Callers passnow - grace; an entry stamped exactly at the boundary has not yet served the full window. An inclusive bound would sweep it a hair early — revert-checked.A malformed reference count fails to decode rather than reading as zero. Zero means "no live reference", so defaulting to it on corruption would make a live blob look collectable — the difference between a space leak and data loss. Revert-checked.
The ordering trap
'-'(0x2D) sorts below'|'(0x7C), so!s3|chunkblob-gc-queue|lands entirely below!s3|chunkblob|rather than inside it. That is the behaviour we want — neither range scan can reach the other's keys — but it is not the behaviour a reader assumes from the names, soTestGCKeyspacesSortOutsideTheChunkBlobRangepins it explicitly. (This is the same class of bug as the!s3route|vs!s3|ordering issue from PR #1088.)Behavior change / risk
New code only. Nothing reads or writes these keyspaces yet, so there is no runtime behavior change and no on-disk footprint until the sweeper lands. The prefixes are newly reserved and collision-tested against the existing chunkblob and chunkref parsers.
Test evidence
go test ./internal/s3keys/ -race -count=1— passgolangci-lint run ./internal/s3keys/...— 0 issues, no//nolintdiff -q):TestChunkBlobGCQueueSortsByEligibilityTimeFAILsTestChunkBlobGCQueueScanEndIsExclusiveFAILsTestChunkRefRCValueFailsClosedOnMalformedValueFAILs11 tests: round-trips, table-driven malformed-input rejection for both parsers, sort order across
0 … MaxUint64, boundary exclusivity, lower-bound coverage, separator unforgeability, and cross-keyspace collision.Self-review (five passes)
https://claude.ai/code/session_013rNHooj7NF3giihWVba8QE
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