Event Indexing

SellPolia has no “submit order” button — the chain is the source of truth. A deposit becomes a queue order, and a payment becomes a filled buy, purely by the backend watching contract events. Every chain is indexed the same way, with two paths that funnel into one idempotent processor (so a log seen by both is handled exactly once).

1. WebSocket subscription (real-time)

A low-latency eth_subscribe("logs", …) subscription (viem watchEvent with poll: false) streams matching logs for the contract as they happen. This path is stateless and reconnects with exponential backoff if the socket drops.

2. HTTP getLogs sweep (backstop)

A periodic sweep re-scans from a stored cursor up to head − confirmations in batches (500 blocks at a time). It runs immediately at startup to backfill any downtime, then repeats on a per-chain interval. The sweep owns the cursor; the WebSocket path just accelerates delivery.

Together they give real-time updates with a self-healing backstop — if the socket misses a log, the next sweep catches it.

What gets indexed

Idempotency

• Vault deposits are keyed by (blockNumber, logIndex).
• Purchases are keyed by chainId:txHash:buyer:recipient — deliberately not log-index based, so the key is stable even if a reorg reshuffles logs.