The rain engine

The rain engine is Rainfall's keeper. It runs every hour at :00 UTC as a scheduled job, and handles each coin in turn within a fixed time budget. A coin that does not fit in one run is picked up first in the next.

One round, step by step

1. Round id. The round is named <mint>:<YYYYMMDDHH> and written to the keeper's store before any transaction is sent. A round id that exists is never sent again.
2. Collect. The keeper finds the coin's token accounts with withheld tax (a getProgramAccounts scan of Token-2022 filtered on the mint, paged and capped per round), harvests them into the mint in batches, then withdraws from the mint to its own account with withdrawWithheldTokensFromMint.
3. Sell. It sells the collected tokens for SOL on the LaunchLab curve before graduation, or on the CPMM pool after. Each round sells at most 2 % of the coin's volume over the last hour; the rest is carried to the next round, so the engine never weighs on the price.
4. Add LP fees. After graduation the keeper also harvests the locked LP's fees with the Fee Key and adds the SOL to the same round.
5. Pay. The SOL is split pro rata to balances. Every holder whose share is at least 0.00005 SOL is paid in batches of SOL transfers; the first transaction of the round carries the Memo rainfall:rain:<mint>:<round>. Smaller shares are carried over to that holder's next round.
6. Record. The round (time, tokens collected, SOL rained, holders paid, every payout signature) is written to the store and shown in the coin's rain ledger.

Who is never paid

The LaunchLab curve vault, the CPMM pool vaults, the burn address and Rainfall's own keys. A wallet address that does not exist yet on chain (zero SOL) cannot receive less than Solana's rent minimum, so its share is carried over until it reaches that minimum or the wallet holds SOL.

Costs

Transaction fees and account rent for payouts are paid from the keeper's own SOL, which half of every platform fee claim refills (see $RAIN). Holders receive the SOL from the sale in full, after the curve or pool fees of that sale and the tax on the sale transfer itself.