RFC-001: Symbol Sharding for Quote Fan-Out

Status: Proposed, REV C. This sheet is open for comment. It does not change the flight binary until the comment ledger marks it accepted.

Problem

A single fan-out process cannot own every symbol. The head of the book — a handful of names — pins one core, while the long tail sits idle. Subscribers still expect one socket.

Proposal

Shard by symbol on a consistent-hash ring with virtual nodes. Each shard owns three things only:

• Normalization for its symbol set
• The subscriber interest index
• The per-connection credit window for those symbols

Rules

• A symbol has one owner. Two owners is a defect, not a feature.
• Resharding moves virtual nodes, not client sockets. The edge rewrites the route.
• Heartbeats are per shard. Two misses and the interest entry is dropped. The tally is public on RT-500.
• Slow consumers lose ticks. They do not stall the shard.

Budget

The cover sheet still holds a 100 ms ceiling from exchange tick to phone screen. Shard lookup is a 1 ms line item (RT-200). Fan-out is 12 ms (RT-210). The handset render sits in the reference workload, not in the bus.

Reference

Stock Picks is the live consumer of this drawing. Open the reference implementation if you want the path under real quotes. Comments belong on the RFC, not in a private thread.