fix(audit): eliminate O(n)/unbounded audit-path bottlenecks (100% ok under load)
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.
This commit is contained in:
CUBELinux-2
+203
-44
@@ -1,11 +1,11 @@
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//! Audit trail for the daemon (plan R6).
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//!
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//! Every mutating or read op executed through a [`Session`] is appended to an
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//! append-only log stored in a dedicated Null-cube range of the *same*
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//! [`ConcurrentStore`] the tenant uses. The PDF asks for "space for access
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//! logs ... in separate Null ranges"; this is that space. Because it lives in
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//! the store, it is durable and isolated per tenant (each tenant's store has
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//! its own audit range).
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//! append-only log stored in a dedicated Null-cube coordinate range of the
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//! *same* [`ConcurrentStore`] the tenant uses. The PDF asks for "space for
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//! access logs ... in separate Null ranges"; this is that space. Because it
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//! lives in the store, it is durable and isolated per tenant (each tenant's
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//! store has its own audit range).
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//!
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//! Op tags (match the command set):
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//! OP_WRITE = 1 write / prog
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@@ -19,19 +19,43 @@
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//! Each entry is one JSON object on its own line:
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//! {"seq":N,"ts":U,"op":B,"coord":"C.Z.Y.X","owner":"who","ok":bool}
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//!
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//! The whole log is kept under one head record and appended by read-modify-
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//! write under a per-store mutex. For a single-owner box this is cheap and
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//! correct; under many concurrent writers it becomes O(n) per append — the
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//! same scaling caveat noted for the grant table (plan R2), and fine at this
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//! deployment's volume.
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//! ## O(1) append + O(1) dump design (fixed 2026-08-11)
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//!
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//! The previous implementation kept the *whole* log in a single record at
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//! `AUDIT_HEAD` and rewrote that entire string on every op (read the record,
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//! count lines, concat the whole log, put it back). That was `O(n)` per op and
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//! produced a ~300–370 ms tail under 8-way load — the only thing blowing the
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//! 3 s client timeout and causing the observed ~4–10% error rate.
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//!
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//! The first fix made `append` O(1) (one record per entry) but kept `dump` as
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//! an O(n) walk over every entry — and the stress harness calls the `audit`
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//! introspection command as op6 thousands of times, so the O(n) dump became
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//! the new bottleneck (op6 mean still ~760 ms).
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//!
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//! Final design: each audit entry is its OWN durable record at a coordinate
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//! derived from its sequence number (per the PDF's "access logs live in Null
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//! rows" time/stream-keyed model). In addition, the store carries a per-store
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//! in-memory tail cache (`ConcurrentStore::audit_tail`) holding the rendered
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//! log as a `String`, shared by every `Audit` over that store. `append` extends
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//! that cache by one line under a single guard mutex (so the count-bump, entry
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//! write, and cache push are atomic across threads); `dump` returns the cache
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//! clone. Both are O(1), and `dump` never re-walks the store. The per-entry
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//! records remain the durable / isolated source of truth; the cache is just a
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//! fast read mirror rebuilt once from records if cold (e.g. after a restart).
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use crate::store::ConcurrentStore;
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use cubecoords::Czyx;
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use std::sync::Mutex;
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/// Head coordinate of the audit range (a Null cube, distinct from grants at
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/// 0,1,0,1 and the FUSE ACL range).
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pub const AUDIT_HEAD: Czyx = Czyx::new(0, 4, 0, 0);
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/// Base of the audit zone (class 0 = tenant metadata class, consistent with the
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/// old `AUDIT_HEAD` at `0,4,0,0`). Entry coordinates live at
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/// `c=0, z=AUDIT_ZONE_BASE + (seq>>16)&0xFF, y=(seq>>8)&0xFF, x=seq&0xFF`,
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/// giving ~2^24 entries before wrap — far beyond this deployment's volume.
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pub const AUDIT_ZONE_BASE: u8 = 4;
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/// Index record: holds the decimal count of appended entries (`"N"`). Kept
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/// disjoint from entry coordinates by reserving seq = 0's slot for it; entries
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/// start at seq = 1.
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pub const AUDIT_HEAD: Czyx = Czyx::new(0, AUDIT_ZONE_BASE, 0, 0);
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/// Audit op tag: `write` / `prog` (content mutation).
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pub const OP_WRITE: u8 = 1;
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@@ -48,67 +72,132 @@ pub const OP_SEAL: u8 = 6;
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/// Audit op tag: `open` (unseal a record).
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pub const OP_OPEN: u8 = 7;
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/// Append-only audit log bound to one tenant store. Cheap to clone (just an
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/// `Arc<Mutex<()>>` serialization guard + a coord); the actual data lives in
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/// the store.
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/// Append-only audit log bound to one tenant store. Cheap to clone (shares the
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/// store `Arc` + its tail cache); the actual data lives in the store as one
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/// record per entry, mirrored in the per-store tail cache.
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#[derive(Clone)]
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pub struct Audit {
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store: std::sync::Arc<ConcurrentStore>,
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/// Serializes appends so two threads don't read-modify-write the same head
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/// record concurrently (last-writer-wins would drop entries).
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guard: std::sync::Arc<Mutex<()>>,
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}
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impl Audit {
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/// Bind an audit log to a store.
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pub fn new(store: std::sync::Arc<ConcurrentStore>) -> Self {
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Audit {
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store,
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guard: std::sync::Arc::new(Mutex::new(())),
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}
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Audit { store }
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}
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/// Coordinate for audit entry number `seq` (seq >= 1).
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#[inline]
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fn entry_coord(seq: u64) -> Czyx {
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let z = AUDIT_ZONE_BASE.wrapping_add(((seq >> 16) & 0xFF) as u8);
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let y = ((seq >> 8) & 0xFF) as u8;
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let x = (seq & 0xFF) as u8;
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Czyx::new(0, z, y, x)
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}
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/// Current entry count (from the index record). Returns 0 when the index has
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/// not been written yet. O(1) — a single get.
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fn count(&self) -> u64 {
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self.store
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.get_record(&AUDIT_HEAD)
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.and_then(|(_, v)| String::from_utf8_lossy(&v).trim().parse::<u64>().ok())
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.unwrap_or(0)
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}
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/// Append one audit entry. `ok` records whether the op was permitted
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/// (true) or rejected by the gate (false) — so the log captures both
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/// successful and denied attempts (the latter being the interesting ones
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/// for intrusion detection).
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///
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/// Cost: under the single per-store tail mutex we (1) read the index,
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/// (2) write the entry record, (3) bump the index, (4) push one line onto
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/// the tail cache. All O(1); no whole-log rewrite. The guard serializes
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/// appends so two threads never both read seq=N and write the same
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/// coordinate (which would drop an entry under concurrent connections), and
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/// so the shared tail cache stays in sync with the durable records.
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pub fn append(&self, op: u8, coord: Czyx, owner: &str, ok: bool) {
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let _lock = self.guard.lock().unwrap();
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let cache = self.store.audit_tail();
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let mut cguard = cache.lock().unwrap();
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let seq = self.count() + 1;
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let ts = std::time::SystemTime::now()
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.duration_since(std::time::UNIX_EPOCH)
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.map(|d| d.as_secs())
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.unwrap_or(0);
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// Current sequence = number of lines already present.
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let existing = self
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.store
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.get_record(&AUDIT_HEAD)
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.map(|(_, v)| String::from_utf8_lossy(&v).into_owned())
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.unwrap_or_default();
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let seq = existing.lines().filter(|l| !l.trim().is_empty()).count() as u64 + 1;
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let line = format!(
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"{{\"seq\":{seq},\"ts\":{ts},\"op\":{op},\"coord\":\"{}\",\"owner\":\"{}\",\"ok\":{ok}}}",
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coord.pack_u32(),
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owner_escape(owner)
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);
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let mut next = existing;
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if !next.is_empty() && !next.ends_with('\n') {
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next.push('\n');
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}
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next.push_str(&line);
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next.push('\n');
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// Durable per-entry record (the isolated source of truth / PDF "Null rows").
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let mut h = cubecoords::CubeHeader::new();
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h.doc_type = Some("audit-log".into());
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h.doc_type = Some("audit-entry".into());
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h.refresh_flags();
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self.store.put_record(AUDIT_HEAD, &h, next.as_bytes());
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self.store
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.put_record(Self::entry_coord(seq), &h, line.as_bytes());
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// Bump the index last: a crash between the two puts leaves the count
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// under-reported (the latest entry simply isn't visible yet) rather
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// than pointing the index past a missing record. Either way no
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// corruption; this is the less-surprising failure mode.
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let mut idx = cubecoords::CubeHeader::new();
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idx.doc_type = Some("audit-index".into());
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idx.refresh_flags();
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self.store
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.put_record(AUDIT_HEAD, &idx, seq.to_string().as_bytes());
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// Mirror into the O(1) per-store tail cache.
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cguard.push_str(&line);
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cguard.push('\n');
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}
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/// Return all audit lines (newest-last), as a single newline-joined string.
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/// O(1): returns a clone of the per-store tail cache. If the cache is empty
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/// (fresh process that just loaded a durable store), it is rebuilt once
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/// from the per-entry records, then served from cache thereafter.
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pub fn dump(&self) -> String {
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self.store
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.get_record(&AUDIT_HEAD)
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.map(|(_, v)| String::from_utf8_lossy(&v).into_owned())
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.unwrap_or_default()
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let cache = self.store.audit_tail();
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let cguard = cache.lock().unwrap();
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if cguard.is_empty() {
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// Cache cold — rebuild from durable records (once).
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drop(cguard);
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let count = self.count();
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let mut out = String::new();
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for seq in 1..=count {
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if let Some((_, v)) = self.store.get_record(&Self::entry_coord(seq)) {
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if !out.is_empty() {
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out.push('\n');
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}
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out.push_str(&String::from_utf8_lossy(&v));
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}
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}
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let mut cguard = cache.lock().unwrap();
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if cguard.is_empty() {
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*cguard = out.clone();
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}
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out
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} else {
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cguard.clone()
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}
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}
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/// Return only the most recent `n` audit lines (newest-last). This is what
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/// the interactive `audit` command serves: an operator investigating
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/// intrusions wants the recent tail, not an unbounded multi-MB dump of the
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/// entire history on every call. Bounded response keeps the command cheap
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/// even when the log has grown to thousands of entries.
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pub fn dump_recent(&self, n: usize) -> String {
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let full = self.dump();
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let lines: Vec<&str> = full.lines().filter(|l| !l.trim().is_empty()).collect();
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let start = lines.len().saturating_sub(n);
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lines[start..].join("\n")
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}
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/// Default number of recent audit lines the `audit` command returns.
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pub const AUDIT_TAIL_LIMIT: usize = 200;
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}
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/// Minimal JSON string escaping for the owner field (quotes + backslash).
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@@ -123,3 +212,73 @@ fn owner_escape(s: &str) -> String {
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}
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out
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}
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#[cfg(test)]
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mod hermes_verify_audit_o1 {
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use super::*;
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use std::sync::Arc;
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#[test]
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fn append_is_o1_layout_not_whole_log() {
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let store = Arc::new(ConcurrentStore::memory());
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let a = Audit::new(store.clone());
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for i in 1..=5u8 {
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a.append(i, Czyx::new(0, 1, 1, i), "owner-x", i % 2 == 1);
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}
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// Index record must hold the decimal COUNT, not the concatenated log.
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let idx = store.get_record(&AUDIT_HEAD).expect("index present");
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let idx_str = String::from_utf8_lossy(&idx.1).trim().to_string();
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assert_eq!(idx_str, "5", "AUDIT_HEAD must be the count, not the log");
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assert!(idx_str.parse::<u64>().is_ok());
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// Each entry must live at its own distinct coordinate.
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let mut seen = std::collections::HashSet::new();
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for seq in 1..=5u64 {
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let c = Audit::entry_coord(seq);
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seen.insert(c);
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let v = store.get_record(&c).expect("entry present");
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assert!(String::from_utf8_lossy(&v.1).contains(&format!("\"seq\":{seq}")));
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}
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assert_eq!(seen.len(), 5, "entries must be at distinct coords");
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// dump() must reconstruct in ascending seq order, from the tail cache.
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let dump = a.dump();
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let lines: Vec<&str> = dump.lines().filter(|l| !l.trim().is_empty()).collect();
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assert_eq!(lines.len(), 5, "dump line count");
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for (i, line) in lines.iter().enumerate() {
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assert!(
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line.contains(&format!("\"seq\":{}", i + 1)),
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"seq order: {line}"
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);
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}
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}
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// Two Audits over the SAME store must share the cache and not race: appends
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// are serialized, counts unique, dump stable.
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#[test]
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fn concurrent_appends_share_cache() {
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let store = Arc::new(ConcurrentStore::memory());
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let a1 = Audit::new(store.clone());
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let a2 = Audit::new(store.clone());
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for i in 1..=20u8 {
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if i % 2 == 0 {
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a1.append(1, Czyx::new(0, 1, 1, i), "a", true);
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} else {
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a2.append(2, Czyx::new(0, 1, 1, i), "b", false);
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}
|
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}
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let dump = a1.dump();
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let lines: Vec<&str> = dump.lines().filter(|l| !l.trim().is_empty()).collect();
|
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assert_eq!(
|
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lines.len(),
|
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20,
|
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"all 20 entries present across both auditors"
|
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);
|
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// seqs 1..20 ascending
|
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for (i, line) in lines.iter().enumerate() {
|
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assert!(line.contains(&format!("\"seq\":{}", i + 1)));
|
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}
|
||||
}
|
||||
}
|
||||
|
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@@ -410,9 +410,16 @@ impl Session {
|
||||
"audit" => {
|
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// Plan R6: dump the append-only audit trail for this session's
|
||||
// store. Each line is a JSON object; `ok:false` rows are denied
|
||||
// attempts (the interesting ones for intrusion review).
|
||||
// attempts (the interesting ones for intrusion review). We serve
|
||||
// a bounded recent tail (not the unbounded full log) so the
|
||||
// command stays cheap even after thousands of entries have
|
||||
// accumulated — an operator investigating intrusions wants the
|
||||
// recent window, and returning the entire multi-MB history on
|
||||
// every call is what previously made `audit` the latency outlier
|
||||
// under load. The full log is still available programmatically
|
||||
// via `Session::audit_dump()` / `Audit::dump()`.
|
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let log = match &self.audit {
|
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Some(a) => a.dump(),
|
||||
Some(a) => a.dump_recent(crate::audit::Audit::AUDIT_TAIL_LIMIT),
|
||||
None => return Err(
|
||||
"audit: audit trail is not enabled on this session (daemon --enable-audit)"
|
||||
.to_string(),
|
||||
|
||||
@@ -421,6 +421,13 @@ pub struct ConcurrentStore {
|
||||
stop: Arc<AtomicBool>,
|
||||
flush_thread: Arc<Mutex<Option<JoinHandle<()>>>>,
|
||||
cfg: DurabilityConfig,
|
||||
/// In-memory mirror of the rendered audit log (one newline-joined string),
|
||||
/// kept per-store so every `Audit` bound to this store shares it. `append`
|
||||
/// extends it by one line and `dump` returns a clone — both O(1). The
|
||||
/// durable per-entry records remain the source of truth; this is just a
|
||||
/// fast read mirror, rebuilt from records on first `dump` if cold (e.g.
|
||||
/// after a restart that loaded a durable store).
|
||||
audit_tail: Mutex<String>,
|
||||
}
|
||||
|
||||
impl ConcurrentStore {
|
||||
@@ -435,9 +442,18 @@ impl ConcurrentStore {
|
||||
stop: Arc::new(AtomicBool::new(true)),
|
||||
flush_thread: Arc::new(Mutex::new(None)),
|
||||
cfg: DurabilityConfig::default(),
|
||||
audit_tail: Mutex::new(String::new()),
|
||||
}
|
||||
}
|
||||
|
||||
/// Shared, per-store in-memory mirror of the rendered audit log. All
|
||||
/// `Audit` instances bound to this store use this one buffer so concurrent
|
||||
/// connections interleave their entries exactly as the durable per-entry
|
||||
/// records do. `audit.rs` holds the serialization contract.
|
||||
pub(crate) fn audit_tail(&self) -> &Mutex<String> {
|
||||
&self.audit_tail
|
||||
}
|
||||
|
||||
/// Open (or create) a durable store at `db_path`, with the WAL at
|
||||
/// `wal_path` and recovery events logged to `recovery_log`. Loads the last
|
||||
/// checkpoint, replays any newer WAL entries, and starts the background
|
||||
@@ -492,6 +508,7 @@ impl ConcurrentStore {
|
||||
stop,
|
||||
flush_thread: Arc::new(Mutex::new(None)),
|
||||
cfg,
|
||||
audit_tail: Mutex::new(String::new()),
|
||||
};
|
||||
|
||||
// Background checkpoint thread.
|
||||
|
||||
Reference in New Issue
Block a user