zlay#

an AT Protocol relay in zig. crawls PDS hosts directly and rebroadcasts their firehose as a single aggregated stream.

live instance: zlay.waow.tech — metrics dashboard

what it does#

a relay subscribes to every PDS on the network, verifies commit signatures, and serves the merged event stream to downstream consumers via com.atproto.sync.subscribeRepos. it also maintains a collection index for com.atproto.sync.listReposByCollection.

design#

• direct PDS crawl — no fan-out relay in between. the bootstrap relay (bsky.network) is called once at startup for the host list, then all data flows from each PDS.
• optimistic validation — on signing key cache miss, frames pass through immediately and the DID is queued for background resolution. >99.9% cache hit rate after warmup.
• inline collection index — RocksDB with two column families for bidirectional (DID, collection) lookups. no sidecar process.
• one thread per PDS — predictable memory, no GC. ~2,750 threads is fine; most are blocked on websocket reads.

dependencies#

endpoints#

build#

requires zig 0.15 and a C/C++ toolchain (for RocksDB).

zig build                          # build
zig build test                     # run tests
zig build -Doptimize=ReleaseSafe   # release build

see docs/deployment.md for production deployment and docs/backfill.md for collection index backfill.

numbers#