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03 / NOTES & OBSERVATIONS

Thinking out loud.
In writing.

Long-form engineering essays, worked examples and readings of research papers. On systems, their edges, and the decisions that survive contact with the real world.

THE NOTEBOOK78 ENTRIES

Notebook dates are assigned across June 2025–September 2026 to organise this collection. Each essay lists its publication date separately.

SYSTEMS

14 ESSAYS

Engineering essay · 7 MIN READ

Fuzzing the parser boundary

Build a parser fuzz target around bounded resources, explicit rejection and semantic oracles, then preserve useful counterexamples.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Floating-point is an error budget

Choose numeric representations, tolerances and stable algorithms from the meaning of the result rather than a blanket rule about decimals.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Arena allocation and the cost of reset

Arena allocation simplifies allocation only when object lifetimes, cleanup and retention agree with the reset boundary.

EDITORIAL DATE

Engineering essay · 7 MIN READ

io_uring and buffer ownership

Model submitted buffers, terminal completions, cancellation and zero-copy notifications as an explicit ownership protocol.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Why “unknown” should be a valid system output

Abstention as a decision with a cost, and a Rust contract that keeps unsupported conclusions separate from negative answers.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Lock-free is not wait-free

Separate system-wide progress, individual completion and elapsed deadlines when evaluating concurrent algorithms.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Bounded queues are a product decision

Queue capacity determines which promises a service makes under load. Backpressure, rejection and deadlines have different user-visible meanings.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Property tests need a model

Generated inputs become valuable when an independent model, meaningful invariants and intentional generators define what should happen.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Rust async without a runtime: what that actually means

Futures define a polling contract. Executors, wakeups, I/O drivers and scheduling policy are separate responsibilities that still need an owner.

EDITORIAL DATE

Engineering essay · 7 MIN READ

When Go is the right rewrite

A rewrite should remove a measured constraint while preserving the service's real contract. Go's runtime is a tradeoff to evaluate, not a verdict.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Cancellation is a protocol

Stopping local waiting does not undo remote work. A reliable cancellation design needs ownership, acknowledgements and a clear commit boundary.

EDITORIAL DATE

Engineering essay · 7 MIN READ

State machines need invalid transitions

A useful state machine specifies rejected events, guards, atomic transitions and recovery as carefully as its happy path.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Designing systems for uncertainty

Freshness, provenance and conflicting observations belong in the data contract, before a consumer decides what to do.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Memory ordering without mysticism

Reason about atomic publication through happens-before edges, ownership and concrete failure cases rather than processor folklore.

EDITORIAL DATE

PERFORMANCE

20 ESSAYS

Engineering essay · 7 MIN READ

Latency budgets need critical paths

Budget user-visible latency through dependency graphs, queue boundaries and deadlines rather than adding every span or percentile.

EDITORIAL DATE

Engineering essay · 7 MIN READ

False sharing is a layout bug

Distinguish logical independence from coherence traffic, then change layout only when ownership and measurements support it.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Zero-copy is a lifetime decision

Avoiding a copy changes who owns memory, how long buffers stay alive and which boundaries can safely share them.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Indexes are a write-path decision

Evaluating indexes as maintained data structures with consequences for updates, storage, concurrency and the full query workload.

EDITORIAL DATE

Engineering essay · 8 MIN READ

Small models and the cost of a decision

Reason about tiny learned runtimes through total decision latency, feature costs, precision, fallback behavior and honest benchmarks.

EDITORIAL DATE

Paper analysis · 7 MIN READ

The tail is the system

Reading Dean and Barroso through fan-out, correlated slowdowns and the resource budget that makes hedging succeed or fail.

EDITORIAL DATE

Engineering essay · 7 MIN READ

CPU time is not wall time

Separate execution, waiting and parallel work before turning elapsed time or CPU utilization into a performance diagnosis.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Cache locality before cleverness

The representation that exposes useful bytes can matter more than a clever loop. Start with access patterns, working sets and ownership between cores.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Profile the production shape

A profile estimates where a particular workload spent resources. Make its population, sampling and attribution boundaries explicit.

EDITORIAL DATE

Engineering essay · 7 MIN READ

SIMD begins with a data contract

Vectorization depends on aliasing, numeric semantics, tails and deployment capabilities before instruction width becomes useful.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Prefix caching needs an identity

A prefix cache is correct only when its key identifies the computation, its authorization scope and the inputs that produced the cached state.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Performance regressions need experiments

Design comparative CI experiments around pairing, practical effect sizes and controlled environments instead of brittle timing thresholds.

EDITORIAL DATE

Paper analysis · 7 MIN READ

The KV cache is a systems problem

A PagedAttention reading focused on memory accounting, fragmentation, ownership, scheduling and serving trade-offs.

EDITORIAL DATE

Engineering essay · 7 MIN READ

7.4 microseconds: what a benchmark must explain

A reported median is the beginning of a performance argument. Measurement boundaries, sampling and workload design determine what it means.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Open-loop load tests tell a different story

Arrival schedules, coordinated omission and generator limits determine what a load test can honestly say about overload.

EDITORIAL DATE

Paper analysis · 7 MIN READ

Mixture of experts still needs a scheduler

Sparse expert activation saves arithmetic only within a system that can route tokens, balance capacity and control communication costs.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Bloom filters spend false positives

Sizing Bloom filters, pricing false positives and preserving the conditions under which a negative answer is trustworthy.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Syscalls are not the whole I/O cost

Account for copies, cache state, queueing and durability before attributing I/O performance to system-call counts.

EDITORIAL DATE

Engineering essay · 7 MIN READ

LSM trees move the write cost

Understanding log-structured storage through compaction debt, read and space amplification, tombstones and sustainable throughput.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Quantization moves the error

A worked quantization and bias-correction example shows why small weight error does not guarantee small decision error.

EDITORIAL DATE

AI

21 ESSAYS

Engineering essay · 7 MIN READ

Context compression can delete the proof

Token reduction is useful only when compressed context preserves the evidence, exceptions and uncertainty needed to justify the answer.

EDITORIAL DATE

Engineering essay · 8 MIN READ

Backpressure for streaming AI

Bound token and audio streams with explicit queue budgets, cancellation, fair scheduling and honest completion semantics.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Tool permissions need capabilities

Agent tools need narrow, enforceable authority over operations and resources, with explicit limits for delegation, expiry and commitment.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Embeddings are a versioned interface

An embedding migration changes the meaning of distance. Treat the encoder, corpus and index as one versioned retrieval contract.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Evaluating AI without grading the vibes

Build evaluations around decisions, paired comparisons, error costs and reproducible conditions rather than polished answers.

EDITORIAL DATE

Paper analysis · 7 MIN READ

Speculative decoding spends parallelism

The exact sampling correction behind speculative decoding, with a worked acceptance example and realistic cost boundaries.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Synthetic data needs a failure model

Generated examples can expand coverage or erase it. Analyse selection bias, recursive replacement and verification before treating volume as new information.

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Engineering essay · 7 MIN READ

Prompt injection is a data boundary

Defensive design for keeping retrieved text, tool output and model suggestions from acquiring application authority.

EDITORIAL DATE

Engineering essay · 7 MIN READ

AI evaluation needs a dataset lifecycle

A benchmark is a versioned measurement instrument. Track provenance, split related cases together and make corrections without silently rewriting the result.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Chunking is an information boundary

A retrieval chunk decides which qualifiers, relationships and source identities remain available when a passage is read alone.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Voice AI should prepare before you stop talking

A design for speculative voice responses that separates listening, preparation, commitment and cancellation.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Speech interruption is a state machine

Stopping a voice assistant requires more than cancelling generation. Invalidate stale audio, control playback and reconcile what the user actually heard.

EDITORIAL DATE

Paper analysis · 7 MIN READ

LoRA is a capacity choice

A reading of LoRA through rank, parameter counts, deployment identity and the limitations of low-rank adaptation.

EDITORIAL DATE

Paper analysis · 7 MIN READ

Attention is a memory interface

Reading Attention Is All You Need through addressing, data movement, masking and the limits of weighted retrieval.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Model routing needs a fallback contract

Routing between models needs explicit quality, latency, privacy and action semantics when the preferred path fails or escalates.

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Engineering essay · 7 MIN READ

Retrieval needs an abstention policy

Why retrieved text is not enough: evidence contracts, claim-level support and risk-versus-coverage decisions for RAG.

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Engineering essay · 7 MIN READ

Reranking is a budget allocation problem

How candidate recall, cross-encoder cost and evidence coverage determine where a retrieval system should spend its reranking budget.

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Engineering essay · 7 MIN READ

Decoding is part of the product

Temperature, truncation and stopping rules change the behaviour users receive. Treat decoding as a versioned product policy, with task-specific evaluation.

EDITORIAL DATE

Engineering essay · 8 MIN READ

Agents need transaction boundaries

Design AI tool execution around proposals, durable intent, idempotency, stale state and uncertain external outcomes.

EDITORIAL DATE

Engineering essay · 8 MIN READ

Structured output is not semantic correctness

A typed AI response can still be false, stale or unauthorized. Design validation around the decision it will drive.

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Engineering essay · 7 MIN READ

Agent memory needs forgetting

Durable agent memory needs retention, provenance, correction and deletion semantics that remain valid across summaries and indexes.

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INFRASTRUCTURE

10 ESSAYS

Engineering essay · 7 MIN READ

Disaster recovery is a replay budget

Deriving recovery objectives from durable copies, restore throughput, replay capacity, dependency recovery and verified cutover.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Cross-chain funding attribution: evidence before interpretation

A rigorous model for cross-chain traces that separates observations, bridge joins, conservation checks and uncertain attribution.

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Engineering essay · 7 MIN READ

Tracing needs context, not just spans

Building useful traces through causal propagation, asynchronous boundaries, sampling and controlled diagnostic context.

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Engineering essay · 7 MIN READ

Retry budgets prevent amplification

Treating retries as additional load with a finite budget, coordinated deadlines and explicit rules for ambiguous operations.

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Engineering essay · 7 MIN READ

Cardinality is an observability budget

Budgeting metric series through label combinations, histogram expansion, churn and the questions each dimension must answer.

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Engineering essay · 7 MIN READ

Rate limits need a fairness policy

Why a request counter cannot decide fair access, and how identities, cost weights, concurrency and reserved capacity change admission.

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Engineering essay · 7 MIN READ

Backfills that do not fight production

Design resumable backfills around consistent cuts, conditional writes, adaptive resource budgets and verifiable completion.

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Engineering essay · 7 MIN READ

Zero-downtime migrations need expand-contract

Planning database changes as overlapping application versions, bounded data work and evidence-based removal of old schema.

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Engineering essay · 7 MIN READ

Replay is an architectural feature

A retained event log becomes a recovery tool only when inputs, transformations, side effects, checkpoints and output comparison support replay.

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Engineering essay · 7 MIN READ

Pagination needs a consistency contract

Choosing between live traversal and stable snapshots, with deterministic keyset ordering and explicit cursor semantics.

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DISTRIBUTED SYSTEMS

13 ESSAYS

Engineering essay · 7 MIN READ

WebSocket reconnection is state reconciliation

Reconnect a live application with explicit cursors, consistent snapshots, bounded replay and application acknowledgements rather than a socket retry alone.

EDITORIAL DATE

Engineering essay · 7 MIN READ

Cache invalidation is a versioning problem

Making cache freshness explicit with complete keys, source versions, guarded fills and recovery rules for missed invalidations.

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Paper analysis · 7 MIN READ

Event time is not wall-clock time: reading the Dataflow paper

An analysis of the Dataflow model through late events, watermarks, revisions and the application decisions that a streaming engine cannot make.

EDITORIAL DATE

Engineering essay · 7 MIN READ

The dual-write problem: what an outbox actually guarantees

An outbox makes a database change and publication intent atomic; delivery, ordering, deduplication and consumer effects still need their own contracts.

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Engineering essay · 7 MIN READ

Multi-region is a failure model

Designing regional resilience through quorum placement, replication lag, failover authority, capacity headroom and shared dependencies.

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Paper analysis · 7 MIN READ

Raft is a replicated state machine contract

Reading Raft through its application boundary: commitment, deterministic execution, retries, membership changes and trustworthy reads.

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Engineering essay · 7 MIN READ

Leases need fencing tokens

Why an expired lease cannot stop an old worker, and how resource-enforced fencing turns ownership changes into safe writes.

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Engineering essay · 7 MIN READ

Isolation levels are observable behaviour

Understanding transaction isolation through concurrent histories, write skew, retries and the invariants users can observe.

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Engineering essay · 7 MIN READ

Webhooks are a distributed systems problem

Treat webhook receipt, processing, ordering and reconciliation as separate contracts instead of assuming an HTTP callback is a reliable queue.

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Engineering essay · 7 MIN READ

Configuration rollouts are distributed writes

Treating configuration activation as versioned state replication with validation, compatibility, canaries and recovery from missed updates.

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Paper analysis · 7 MIN READ

Ordering events without a global clock: reading Lamport

Lamport clocks preserve causal order without measuring elapsed time; this analysis works through their guarantees, limits and practical alternatives.

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Engineering essay · 7 MIN READ

Exactly once needs a boundary

Exactly-once claims become useful when they specify the effect, transaction boundary, identity, retention window and recovery assumptions.

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Engineering essay · 7 MIN READ

Schema evolution without flag days

Evolve distributed contracts with explicit compatibility directions, semantic migration, expand-and-contract rollout and archived replay fixtures.

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Paper analyses credit the original work; the arguments and worked examples are my interpretation. Subscribe via RSS for new essays.