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two-sided-marketplace

two-sided marketplace

Etsy, Airbnb

SystemTechniques · 21Primitives · 75 two-sided-marketplace Deterministic simulation testingdistributed · medium: Run the whole system in one thread under a seeded scheduler with simulated network, disk and clock, so every failure replays from its seed.›Primary-backup replicationdistributed · medium: One node orders all writes and ships them to standbys; the acknowledgement rule (none, one, all) sets what a crash loses, and an external arbiter decides who takes over.›Inventory reservationfinance · medium: Reserving stock with TTL holds, release on timeout and no overselling under contentionPayment state machinefinance · medium: Persisted state machine for a payment lifecycle (authorize, capture, void, refund) that treats timeouts as unknown, retries with the same key and applies webhooks idempotently.›Gradient-boosted decision trees (GB…machine-learning · medium: Add small regression trees one at a time, each fitted to the loss gradient; histogram splits over 256 bins make it the strongest tabular default.›Learning to rankmachine-learning · medium: Train a scorer on query-grouped data so that the order it induces maximizes NDCG; LambdaMART (boosted trees with NDCG-weighted pair gradients) is the production default.›Two-tower retrievalmachine-learning · medium: Two separate encoders map users/queries and items into one vector space; item vectors are precomputed and searched by nearest neighbour, so recall over millions costs one small forward pass.›Idempotency keysfinance · low: Client-chosen unique key per logical operation, stored with a request fingerprint and the final response, so retries replay the first result instead of acting twice.›Embeddingsmachine-learning · low: A learned table mapping discrete ids to dense vectors: gather forward, sparse scatter-add backward, row-wise optimizers to keep huge tables cheap.›BM25 rankingsearch-sort · low: The standard lexical relevance score: IDF-weighted term frequency with saturation (k1) and length normalization (b); default in Lucene, Elasticsearch and SQLite FTS5.›Hdr histogramdata-structures · low: Log-linear bucketed histograms with bounded relative error for latency percentilesDouble-entry ledgerfinance · low: Append-only journal of transactions whose postings sum to zero per currency; balances are derived, so money can only move, never appear or vanish.›Largest remainder roundingfinance · low: Splitting an amount into parts that sum exactly (largest remainder / Hamilton) for allocations, splits and prorationsGeospatial cell index (geohash, S2,…geometry · low: Map a lat/lon to a 64-bit cell id on a hierarchical grid, so "near" becomes an integer range scan in any ordinary sorted index.›Process supervisionhardware-os · low: A parent process starts services, reaps their exits and restarts them under a delay and burst-limit policy, then stops them with SIGTERM before SIGKILL.›WebSocketsnetworking · low: Full-duplex message framing over one upgraded HTTP connection; the standard way to push real-time data to browsers.›Mutual TLSsecurity · low: TLS where the client also proves a certificate key, so every connection carries a verified, rotatable machine identity.›Bayesian average ratingstatistics · low: Score = (C·m + sum of ratings)/(C + n): the posterior mean under a prior worth C ratings, so items with few ratings sit near the global mean.›Graceful drainingsystems · low: On a termination signal, stop taking new work, finish in-flight work until a deadline, tell clients to reconnect elsewhere, then exit; clients resume from a token.›Sliding-window counterssystems · low: Count events in the last W seconds with a ring of sub-bucket counters; the two-bucket weighted estimate gives rate limits in 16 bytes per key.›Cooperative schedulingconcurrency · low: Green threads/coroutines yielding at await points on a user-space schedulerRecord replaydistributed · low: Record every nondeterministic input (time, randomness, I/O, model and tool outputs, per-tick player input) and re-execute deterministically for debugging, replays and state rebuildPRNGs (PCG, xoshiro)numerics · low: Small, fast, statistically strong non-cryptographic generators: PCG32 and xoshiro256**, with seeding, parallel streams and unbiased ranges.›+ 14 more techniques+ 59 more primitives

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