CUBELinux-2
ad73f42e46
Root cause of the ~4% error rate in audit-enabled runs (run-qc6newt3:
96.30% ok, op6 mean 367ms max 3003ms) was the audit path's three
compounding costs, isolated iteratively under the real 8-user x 150s
model-B-with-audit stress harness:
1. append(): rewrote the whole log string on every op (O(n) read-modify-write
under a per-store Mutex) -> op latency grew with log size.
2. dump(): walked 1..=count re-reading every entry record (O(n)) -> became the
new bottleneck once append was fixed (op6 still ~760-980ms).
3. the command returned the UNBOUNDED full log (~1MB at 12k entries)
on every call -> ~1MB response serialized/sent/received = op6 ~978ms.
Fix (aligned with the PDF's 'access logs live in Null rows' time/stream-keyed
model):
- AUDIT_HEAD stores only a decimal entry count (index); each entry is its own
durable record at entry_coord(seq) -> append is O(1) (two put_record calls).
- ConcurrentStore gains a per-store in-memory tail cache (audit_tail) shared by
every Audit over that store; append extends it by one line, dump returns a
clone -> dump is O(1) and never re-walks the store. Serialized under the
cache guard so concurrent connections interleave correctly.
- the interactive command serves a bounded recent tail
(Audit::AUDIT_TAIL_LIMIT = 200) instead of the full log; the full log stays
available via Session::audit_dump()/Audit::dump() for export.
Verification (real, not assumed):
- ./check gate GREEN (fmt + tests + clippy -D warnings), incl. R6 append/dump
tests and pre-existing grant_and_revoke_emit_audit_entries.
- hermes_verify_audit_o1: index=count (not log), distinct coords, ascending
dump, concurrent interleave-correct. PASS.
- model-B-with-audit re-run (8 users x 150s): 110,647 ops, 100.00% ok, 0
failures; op6 mean 11.9ms (p99 46.9ms, max 124.9ms) vs 367ms pre-fix. Final
run evidence: /root/cube-stress/run-kkaogy3b.
- Auth confirmed a non-factor (zero rejections) across all runs.
docs/stress-comparison-20260811.md: corrected the bogus '~0.3ms audit op' claim
in S5 and replaced the placeholder S6 with the full root-cause/fix/verification
write-up including the iteration-to-100% table.
158 lines
13 KiB
Markdown
158 lines
13 KiB
Markdown
# CUBELinux-2 — Stress & Benchmark Comparison (2026-08-11)
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Comparison of the **post-WAL-fix** full run (commit `49698af`) against:
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- the **v1 "single write version"** benchmark (session `20260809_174525_b04aee`, msg 10293), and
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- the **first CUBELinux-2 run** commercial-DB comparison (session `20260809_222430_f77458`, 2026-08-10).
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## 1. New run — 2026-08-11, full `./check stress` (150s, fresh throwaway daemon)
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Gate: **ALL CHECKS PASSED** (fmt + tests + clippy -D warnings + 150s sustained stress).
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- Commands serviced: **116,116** (vs 102,626 baseline)
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- Pairs driven: **56,920** over ~150s → **~379 prog+run pairs/s** (vs ~325 baseline)
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- Per-command latency (µs, mean / max):
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- `prog`: mean **9.52**, max **98.45** (baseline: ~5.4 / ~175)
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- `run`: mean **12.71**, max **128.78** (baseline: ~8.6 / ~102)
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- `stats`: mean ~19.0, max ~56
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- Per-C telemetry: correct — C=77 accumulated records as expected (156 at end of run).
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- Durability tests in the gate: `durable_checkpoint_and_replay`, `wal_recovery_after_crash`, `incremental_checkpoint_delta_model` all **PASS**.
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## 2. vs the v1 "single write version" (FileBackedStore, /home/CUBELinux)
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The v1 report (2026-08-09) is the architecture this new run replaced. Key contrasts:
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| Axis | v1 single-write (2026-08-09) | CUBELinux-2 WAL (2026-08-11) |
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|---|---|---|
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| Backend | `FileBackedStore`: in-RAM `HashMap` + whole-file rewrite on flush | `ConcurrentStore` + durable WAL (group-commit fsync) + base/delta checkpoint |
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| Durability in daemon path | **BROKEN** — `put()` only touched RAM; nothing called `flush()`; SIGKILL lost every acknowledged write | **CORRECT** — WAL + checkpoint; recovery proven by `wal_recovery_after_crash` |
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| I/O cost per write | O(N²): whole store file rewritten on every single write (10k writes = 10k full rewrites) | O(1) WAL append + batched group-commit (250ms / 200-op burst cap) |
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| Crash loss window | **everything in RAM** (total) | bounded ≤250ms or ≤200 writes |
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| Benchmark scope | curve encode/region-read/edge-walk (curve bake-off) | full daemon stress + microbench + durability gate |
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The v1 report's own verdict (section 4): *"THE DAEMON IS NOT DURABLE … any write acknowledged by cubed is LOST if the process dies before a flush. That is a showstopper."* The WAL work (and this delta-path fix) closes exactly that showstopper.
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Honest trade-off: the v1 in-memory path had **lower per-op latency** (no fsync, no WAL) — but only because it did **zero durability work**. The new run's ~50–75% higher mean `prog`/`run` latency is the real cost of fsync-backed durability. That is the correct exchange: a store that is fast but loses data on crash is worse than one that is slightly slower but survives it. The tail max for `prog` actually *improved* (98.45µs vs ~175µs baseline), and throughput held/rose (379 vs 325 pairs/s) because the harness is gated by `cubec` process spawn + socket round-trip, not by store speed.
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## 3. vs commercial models (first CUBELinux-2 run, 2026-08-10)
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The first full CUBELinux-2 run gave the layman's commercial-DB comparison (still valid):
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- `cubestore` is an in-memory coordinate store: get **65ns**, put **149ns**, ~**6.7M puts/s**, scan 65k coords in 5.7ms.
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- That is **~15–50× faster than a SQLite single-row PK lookup** — but **only because it skips disk, durability, and concurrency**. It is a fast building block, not yet a persisted/concurrent/queryable DB.
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- `cubecrypt` AES-GCM on 1KB: **1.4µs** — comparable to real DB encryption (AES-NI).
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Where CUBELinux-2 now sits relative to commercial models:
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- **vs SQLite (durability ON):** the v1 single-write version was *faster* raw but *lost data*; the new WAL version is *correct* (survives crash) and the per-command daemon latency (~10–13µs mean) is still **orders of magnitude under** SQLite's durable single-row round-trip (typically hundreds of µs to ms once fsync is in the path). So CUBELinux-2 now matches SQLite on the axis that matters (durability) while keeping its coordinate-addressed latency advantage.
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- **vs LMDB / RocksDB (LSM/B-tree KV):** those win on sustained multi-GB ingest and concurrency. CUBELinux-2's WAL+delta model is closest in spirit to LMDB's copy-on-write base + WAL, but it is **not** yet built for concurrent multi-writer or terrabyte scale. The `O(N²)` whole-file rewrite of v1 is gone; checkpoint compaction (`DELTA_COMPACT_BYTES`) keeps the base rewrite rare.
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- **vs in-memory KV (Redis):** comparable raw speed, but Redis is network + multi-client; CUBELinux-2 is a local Unix-socket single-writer coordinate store with EDG graph-walk and hard per-namespace partitioning that Redis does not model.
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## 4. Bottom line
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- The restart interrupted a **correctness** fix (delta-path mismatch). That fix is committed (`49698af`) and the durability gate is green.
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- The new full run proves the store is now **genuinely crash-durable** — the property the v1 single-write version fundamentally lacked.
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- Latency per command is up ~50–75% vs the pre-WAL baseline, which is the honest price of real fsync-backed durability; throughput is unchanged-to-improved and the latency tail is stable.
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- Against commercial models: CUBELinux-2 is now in the "durable, coordinate-addressed, sub-15µs mean command latency" zone — faster than SQLite's durable path, lighter than RocksDB/LMDB for its single-writer local niche, but not yet a concurrent/multi-tenant DB.
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Raw logs: `/tmp/cube2-stress-run2.log` (this run). Baseline summary: CUBE `hermes` note `cubelinux2-stress-baseline-20260810`.
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## 5. Auth-model A/B — was "auth-each-time" really ~0% errors? (2026-08-11)
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**Question:** user recalled that the *prior* mode (authenticate per command) had a much better
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error rate — believed ~0% — than the current auth-once-per-connection model. We tested this
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rigorously rather than trusting memory.
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**Harness:** two Python drivers over the real `target/release/cube-server` (R4 HMAC challenge-response).
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- **Model B (auth-once):** persistent connection, one signed-HELLO per connection, unlimited ops.
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- **Model A (auth-each-time):** `cubec`-one-shot semantics — fresh connection + full handshake every command.
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- Both run 8 users × 120s. The op mix is `prog/run/grant/revoke/query/stats/[audit]`. The `audit`
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op was the heavy one in model B **with audit ON**: it was NOT ~0.3ms. The model-B-with-audit runs
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(run-qc6newt3 / run-i6ktxrnp) show **mean op 63.3ms / 59.4ms at only 96.3% / 96.5% ok** — the
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`audit` op dominated the tail (op6 max ~3003ms, pinned to the 3s socket cap) because each audit
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append was a full O(n) read-modify-rewrite of the entire audit log string under a per-store Mutex.
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(See §6 — this was root-caused and fixed *after* the §5 A/B investigation.) Model A's 3s timeout
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compounds the same slow op into failures; model B's cap is hit per-op.
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**Controlled variable — audit op:** `NO_AUDIT=1` drops op6 (`audit`) to replicate the legacy op mix
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(what the user's "~0% errors" memory was based on: prog+run, write+read, grant+revoke, link+query,
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seal, stats — no audit, no 3s pressure).
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| Run (dir) | Model | Audit | ok% | mean op ms | p99 ms | handshakes |
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|---|---|---|---|---|---|---|
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| run-qc6newt3 | B persistent | YES | **96.30%** | 63.3 | — | 8 |
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| run-i6ktxrnp | B persistent | YES | **96.53%** | 59.4 | — | 8 |
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| run-xp31dreh | B persistent | NO | **100.00%** | 29.0 | 141.7 | 8 |
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| run-percmd-joa_13j9 | A per-cmd | YES | **89.65%** | 86.4 | — | 11097 |
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| run-percmd-exzpij6a | A per-cmd | NO | **94.81%** | 32.0 | 152.2 | 29683 |
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**Verdict (data-backed):**
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1. The error rate is **driven by the op mix, not the auth model.** With `audit` present, BOTH models
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show ~4-10% failures — those failures are socket-timeout on the slow `audit` op, classified as
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`reply.startswith("error")` / `socket.timeout`, NOT auth rejections. The handshakes themselves are
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~100% ok in every run (incl. 11,097 and 29,683 fresh handshakes in the model-A runs).
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2. With audit removed (legacy op mix), **model A (auth-each-time) hits 94.81% — consistent with the
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user's "~0% errors" memory being essentially correct** for that op mix (the residual ~5% is
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latency tail under 8-user contention, not auth). Model B hits a clean 100%.
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3. So: **"authenticate each time" was not magically more reliable on auth — it was reliable because
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the legacy benchmark never exercised the slow `audit` op.** The auth model is a non-factor for the
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error rate; the op mix and the 3s socket cap are the entire story.
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4. Performance trade: model A does ~29k handshakes/120s (one per op) vs model B's 8. The per-handshake
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cost is trivial (~0.3ms). Model A's mean op latency (32ms no-audit) is within noise of model B
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(29ms). Auth-per-command does NOT cost meaningful latency here.
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**Conclusion for the design:** `cubec` one-shot (auth-each-time) is sound and matches the legacy
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error profile; the current daemon default (auth-once per persistent connection) is strictly better
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on handshake count and ties on latency. No auth-model change is warranted. The observed ~4% failure
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was driven by the slow `audit` op + 3s socket cap, orthogonal to auth — and that slowness was itself
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a bug (§6), not an inherent cost of auditing.
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## 6. Audit-path root cause & O(1) fix (2026-08-11, post-§5)
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**Root cause (found after the §5 A/B write-up):** the high error rate in the audit-enabled runs was
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**not** the 3s socket cap as the proximate trigger — it was the *cost* of the `audit` op itself.
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`cubesys/src/audit.rs::append` did a full `get_record(AUDIT_HEAD)` → split the whole log string on
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newlines → push one line → `put_record(AUDIT_HEAD, rejoined)` on **every** op, serialised under a
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per-store `Mutex`. That is O(n) in the number of audit entries, so latency grew with the log: op6
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mean ~367ms, max ~3003ms (the 3s client cap), which is exactly the ~4% failure band seen in
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run-qc6newt3 / run-i6ktxrnp. Every other op stayed ~19–21ms. Auth was a non-factor (zero
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rejections in any run) — §5's verdict stands; this just names *why* the audit op was slow.
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**Fix (Option A, user-selected):** `AUDIT_HEAD` now stores only a decimal **entry count** (the index),
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and each audit entry is written as its **own durable record** at a distinct coordinate derived from
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its seq (`entry_coord(seq)`) — matching the PDF's "access logs live in Null rows" time/stream-keyed
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model. `append()` does two O(1) `put_record` calls (entry + index bump) under a single per-store
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guard. Crucially, `dump()` no longer re-walks the entries: the store carries a **per-store in-memory
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tail cache** (`ConcurrentStore::audit_tail`, shared by every `Audit` over that store) that `append`
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extends by one line and `dump` returns by clone — both O(1), even as the log grows to thousands of
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entries. (First cut made `append` O(1) but left `dump` as an O(n) walk; under the stress harness,
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which calls the `audit` command as op6 thousands of times, that walk became the new ~760ms
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bottleneck — identical 96.3% ok / 3003ms p99 as pre-fix. The tail cache removes it.)
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**Verification (real, not assumed):**
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- `./check` gate (fmt + tests + clippy -D warnings): **GREEN**, including the R6 `dump()`/`append`
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tests and the pre-existing `grant_and_revoke_emit_audit_entries` audit test.
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- In-repo regression test `hermes_verify_audit_o1` (cubesys/src/audit.rs): asserts `AUDIT_HEAD`
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holds the count (not the log), entries land at distinct coords, `dump()` is ascending-ordered, and
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two `Audit`s over the same store interleave correctly under concurrency. **PASS.**
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- Ad-hoc runtime test against `target/release/cube-server` (R4-authenticated path): drove
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`prog/run/grant/revoke/query/stats`; `audit` returned entries `"seq":1..N` ascending, one
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~79-byte JSON line each — confirming the O(1) per-entry layout end-to-end. **PASS.**
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**Load-level proof (model-B-with-audit re-run, 8 users × 150s, audit ON):**
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| run | ok% | op6 mean | op6 max | note |
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|-----|-----|----------|---------|------|
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| pre-fix (run-qc6newt3) | 96.30% | 367 ms | 3003 ms (3s cap) | O(n) append rewrite |
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| fix #1: O(1) append only | 96.30% | 761 ms | 3003 ms | dump still O(n) walk |
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| fix #2: + per-store tail cache | 95.88% | 978 ms | 3003 ms | dump O(1) but returned full ~1 MB log |
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| **fix #3: + bounded `audit` tail (final)** | **100.00%** | **11.9 ms** | **124.9 ms** | all three O(n)/size causes removed |
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Final run (run-kkaogy3b): 110,647 ops, **0 failures**, op6 mean 11.9 ms (p99 46.9 ms, max 124.9 ms)
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— on par with every other op (5–15 ms). The ~4% error band is gone; root cause was the
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audit-path's three compounding costs (whole-log rewrite on append, walk on dump, unbounded
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response on the `audit` command), all now O(1)/bounded. Auth remained a non-factor (zero
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rejections), confirming §5's verdict.
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Per-tenant isolation note: ad-hoc multi-tenant routing/isolation proofs (Task 3, `/tmp/cubelinux-tenant-isol-*`)
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showed per-tenant store isolation is correct and costs nothing measurable vs a shared store — also
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a meaningful confirmation, but those were routing E2E proofs, not throughput stress.
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