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website live chat and customer messaging

Intercom, Crisp

SystemTechniques · 33Primitives · 101 live-chat Citation groundingagentic-ai · medium: Attaching answer spans to retrieved source passages and verifying each claim is supportedCDN and edgecloud · medium: CDNs cache content in hundreds of PoPs near users, cutting latency and egress bills; edge compute runs small code there. Bandwidth price spreads 10x between providers.›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.›Presence trackingdistributed · medium: Heartbeats refresh per-connection TTLs; a user is online while any connection lives, with a grace period that hides reconnect flaps.›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.›Pub/sub fan-outdistributed · medium: Deliver one published message to every subscriber of a topic by sharing one encoded payload and giving each connection a bounded queue with an explicit slow-consumer policy.›Code splitting lazy loadinggraphics · medium: Split bundles at dynamic imports, load chunks on demand, preload critical pathsText chunkingmachine-learning · low: Cut documents into token-bounded pieces along structure boundaries, keeping offsets and section paths, so each piece embeds well and can be cited.›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.›Hdr histogramdata-structures · low: Log-linear bucketed histograms with bounded relative error for latency percentilesMessage sequence numbersdistributed · low: A per-stream counter on every message lets the receiver detect loss, duplicates and reordering, ack cheaply and resume after reconnect with "send from N".›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.›Language identificationmachine-learning · low: Score a text's character n-grams against per-language statistics, after a cheap script check, and return an ISO 639 code with a confidence or "und".›Long pollingnetworking · low: The client asks "anything after cursor X?"; the server holds the request until there is news or a timeout, and the client immediately asks again.›WebSocketsnetworking · low: Full-duplex message framing over one upgraded HTTP connection; the standard way to push real-time data to browsers.›Hybrid search and rank fusionsearch-sort · low: Merge a keyword (BM25) result list and a vector (ANN) list into one ranking, by ranks (RRF) or by normalized scores (convex combination).›Hmac request signingsecurity · low: HMAC canonical-request signatures and presigned URLs (SigV4 style) with expiryMutual TLSsecurity · low: TLS where the client also proves a certificate key, so every connection carries a verified, rotatable machine identity.›Email threadingstorage · low: Threading messages by Message-ID/References (JWZ algorithm) and subject fallbackSessionizationstorage · low: Group events into sessions by inactivity gapsGraceful 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.›Fuzzy string matchingsearch-sort · low: Edit distance, Jaro-Winkler and trigram indexes for approximate name and address matchingHTTP caching semanticsnetworking · low: The rules (RFC 9111) that decide whether a stored response is still fresh, and how a cheap conditional request revalidates it when it is not.›+ 26 more techniques+ 85 more primitives

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