What Is DHT? A Practical Guide to BitTorrent's Distributed Hash Table
Learn how BitTorrent DHT replaces a central tracker with a distributed peer-discovery layer built on Kademlia-style routing.
BT9G / ENGINEERING NOTES
BT9G Labs
Understand the protocols and systems behind decentralized discovery.
Practical engineering notes on BitTorrent, DHT, metadata exchange, peer discovery and distributed search infrastructure.
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Featured guides
How a Magnet Link Becomes File Metadata: The Complete Peer and Metadata Flow
Trace a magnet link from infohash to DHT peer discovery, BEP 10 negotiation, and BEP 9 metadata retrieval.
How BT9G Can Index BitTorrent Metadata at Scale: A Reference DHT Architecture
A reference architecture for BT9G Labs that connects DHT discovery, durable infohash state, metadata acquisition, search indexing, and observability.
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Explore the DHT Deep Dive
DHT foundations
What Is DHT? A Practical Guide to BitTorrent's Distributed Hash Table
Learn how BitTorrent DHT replaces a central tracker with a distributed peer-discovery layer built on Kademlia-style routing.
Kademlia Explained: XOR Distance, Routing, and Why BitTorrent DHT Scales
A practical explanation of XOR distance, iterative lookup, parallelism, and k-buckets in Kademlia-style DHT routing.
How BitTorrent DHT Finds Peers: From Bootstrap to get_peers and announce_peer
Follow a complete BitTorrent DHT peer-discovery flow from an empty routing table to a usable peer list.
InfoHash Deep Dive: BitTorrent v1, v2, Magnet Links, BTIH, and BTMH
Understand how BitTorrent content identifiers are calculated and how v1 and v2 hashes appear in magnet links.
BEP 5 DHT Messages Explained: ping, find_node, get_peers, and announce_peer
A packet-level guide to the core BitTorrent DHT query types defined by BEP 5.
Inside a DHT Routing Table: k-Buckets, Node Churn, and Contact Selection
How k-buckets organize DHT contacts, why stable nodes matter, and how routing tables behave under churn.
Protocols, peers & metadata
Why Does the DHT See So Many InfoHashes? Understanding Swarm Discovery at Internet Scale
Why a DHT observer can encounter a huge stream of infohashes, including active, stale, duplicate, and low-quality observations.
How DHT Crawlers Discover InfoHashes: Active Lookups, Observations, and Responsible Design
A systems-level guide to discovering infohashes from public DHT activity without confusing discovery with metadata acquisition.
How a Magnet Link Becomes File Metadata: The Complete Peer and Metadata Flow
Trace a magnet link from infohash to DHT peer discovery, BEP 10 negotiation, and BEP 9 metadata retrieval.
BEP 9 ut_metadata Explained: Fetching Torrent Metadata from Peers
A technical guide to BEP 9 message types, metadata pieces, validation, and crawler implementation details.
BEP 10 Extension Protocol: How BitTorrent Negotiates Features Without Breaking Compatibility
Understand the extended handshake, dynamic message IDs, and why BEP 10 is the foundation for features like ut_metadata and PEX.
Tracker vs DHT vs PEX: Three BitTorrent Peer-Discovery Mechanisms Compared
Compare centralized trackers, decentralized DHT lookups, and peer exchange as complementary ways to discover swarm participants.
Seeders and Leechers: What the Numbers Mean and How They Are Measured
Understand seeders, leechers, tracker scrape counters, DHT limitations, and why exact global swarm size is hard to measure.
Why Torrent Metadata Retrieval Fails: 10 Real Causes and a Better Retry Model
Diagnose metadata timeouts, dead swarms, unsupported extensions, bad peers, and scheduler mistakes in DHT-based crawlers.
Crawler engineering
Designing a High-Performance DHT Crawler: Architecture, Queues, and Backpressure
A practical architecture for high-throughput DHT observation with bounded memory, efficient UDP handling, and decoupled metadata workers.
What It Takes to Fetch 1,000+ Torrent Metadata Records per Minute
Capacity-plan a metadata pipeline around peer discovery, connection success rates, timeout budgets, and scheduler concurrency.
How to Deduplicate Billions of InfoHash Observations Without Wasting Metadata Work
Design a multi-tier deduplication layer for DHT ingestion using exact keys, Bloom filters, hot caches, and durable state.
Why Failed InfoHashes Should Stay: Designing a Long-Term Retry Scheduler
Build a retry model that preserves historical hashes, backs off cold swarms, and quickly reactivates when fresh activity appears.
Search infrastructure
Building a BitTorrent Search Index: DHT to Metadata to Elasticsearch
An end-to-end architecture for turning decentralized BitTorrent observations into validated, searchable metadata documents.
How BT9G Can Index BitTorrent Metadata at Scale: A Reference DHT Architecture
A reference architecture for BT9G Labs that connects DHT discovery, durable infohash state, metadata acquisition, search indexing, and observability.