No-GC Conformance Profile: YU01-lmax-sequencer

Cross-cutting allocation discipline for every hot-path stage in this state (Gateway encode, input ring, BLP, output ring emit), per LMAX-NO-GC-JAVA.md. Referenced from spec.md NFR-09B02 and enforced by pipeline/validate-no-gc-conformance.sh plus a Gradle noGcTest profile.

"No-GC" means zero steady-state allocation, not GC tuning. Allocation is permitted only at startup (pre-allocating rings, pools, buffers) and at the outermost edges (Gateway converting inbound JSON/String/BigDecimal to internal binary; output handlers converting back to JSON/SQL). Between those edges, nothing is new-ed per event; and the contract is enforced, not hoped for.

Requirements

• NGC-01: Hot-path packages (Gateway encode path, input ring, BLP, output ring) SHALL allocate zero bytes in the steady state; allocation only at startup and the outermost edges.
• NGC-02: A CI allocation gate SHALL run the hot path under -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC with a small fixed heap (-Xms == -Xmx, e.g. 64–128m, -XX:+AlwaysPreTouch) and FAIL on any steady-state allocation (heap exhaustion fails the test).
• NGC-03: Prices/quantities SHALL be long fixed-point (global scale nogc.px.scale, default ×1,000,000) on the hot path; BigDecimal/String conversions only at the edges, with rounding unit-tested against 009 (penny parity).
• NGC-04: Hot-path collections SHALL be Agrona primitive collections or plain arrays; no HashMap/ConcurrentHashMap, no autoboxing, no stream pipelines on the hot path.
• NGC-05: The hot path SHALL make no Instant.now()/clock reads, no RNG/UUID, and no String.format/SLF4J parameterized logging; time and IDs derive from the event/sequence, and logging is binary/async on a separate thread.
• NGC-06: Each hot-path node SHALL run a JIT warm-up replay (nogc.warmup.events) before going live and SHALL support a nightly bounce (snapshot + replay restart) in a configured window.
• NGC-07: The production/perf run profile SHALL use ZGC or Shenandoah as a sub-ms safety net; the demo/C2 profile MAY use JVM defaults but MUST still pass the allocation gate in CI.
• NGC-08: The allocation contract SHALL be validated by HdrHistogram (latency distributions), JFR (jdk.ObjectAllocationSample) / async-profiler alloc mode (allocation attribution), and jHiccup (pause isolation).

Technique table (what replaces what)

Technique	Replaces in 009
Pre-allocated ring of mutable holders	new DTO per request/message
Flyweight over off-heap (UnsafeBuffer) + SBE codec	Jackson ObjectMapper parse/serialize
long fixed-point prices/qty	BigDecimal (roundPrice, setScale, compareTo)
Symbol -> int securityId at the Gateway	String security end-to-end
Agrona primitive collections / arrays	ConcurrentHashMap, HashMap<Integer,…>, streams
Object pooling for domain state	new OrderRecord(), OrderResponse.from(...) per publish
No locks / no atomics (single writer)	ReentrantLock, AtomicLong/Integer
Binary/async logging off the path	SLF4J parameterized logging (varargs boxing)
Time carried in events (ingressNanos)	Instant.now() per mutation
-Xms==-Xmx, -XX:+AlwaysPreTouch	default heap growth/resize jitter
Epsilon GC in tests; ZGC/Shenandoah in prod	G1 defaults

JVM flags and run profiles

Flag	demo/C2	perf (bare metal)	noGcTest (CI)
-Xms == -Xmx (fixed heap)	yes	yes	yes (small, 64–128m)
-XX:+AlwaysPreTouch	yes	yes	yes
-XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC	no	no	yes (the gate)
-XX:+UseZGC (or +UseShenandoahGC)	optional	yes	no
-XX:+UseLargePages / THP	no	yes	no
-XX:+UseNUMA	no	yes (multi-socket)	no
-XX:StartFlightRecording=settings=profile	optional	yes	yes
Core pinning (isolcpus / OpenHFT Affinity)	no	yes	no

Container caveat (C2): large pages, isolcpus, NUMA, and core pinning need host privileges a containerized demo lacks. The demo/C2 profile MUST run correctly without them and MUST still pass the Epsilon allocation gate in CI.

Configuration keys

Key	Default	Purpose
runtime.profile	demo	demo / perf / noGcTest selector.
nogc.px.scale	1000000	Global fixed-point scale (6 dp).
nogc.warmup.events	100000	Synthetic warm-up workload before going live.
nogc.bounce.cron	0 0 3 * * *	Nightly bounce window.
nogc.logging.async	true	Route hot-path logs to an off-thread ring.

Validation

• SC-NGC-01 (gate): pipeline/validate-no-gc-conformance.sh runs each hot-path node under Epsilon and fails on any steady-state allocation; passes when allocation-free.
• SC-NGC-02 (penny parity): fixed-point arithmetic matches 009's BigDecimal outcomes across a rounding fixture.
• SC-NGC-03 (latency): HdrHistogram reports meet the stage budgets in requirements/nonfunctional-delta.md, with no GC-induced tail spikes (jHiccup).
• SC-NGC-04 (banned APIs): static/architectural check asserts hot-path packages contain no BigDecimal, Instant.now(), HashMap/ConcurrentHashMap, stream pipelines, String.format, or SLF4J parameterized logging.
• SC-NGC-05 (determinism): journal replay produces identical state/output.
• SC-NGC-06 (profiles): demo/C2 image runs without perf knobs and still passes the allocation gate; perf profile documented for bare-metal benchmarking.