Ergo-Native Features
Intermediate
2-4 hoursStorage-Rent Aware Contract (Long-Lived State)
Design contracts that survive storage rent: state refresh and rent safety
Problem
Ergo's storage rent can consume boxes after ~4 years if not maintained. Long-lived contracts need to survive rent collection.
Solution
Design contracts with rent awareness: sufficient ERG reserves, refresh mechanisms, and state recreation patterns. Anyone can refresh a box to reset the rent timer.
How It Works
- 1Ergo charges ~0.14 ERG/byte per 4 years for storage
- 2Boxes below minimum value can be collected by miners after rent period
- 3Refresh = spend and recreate box with same state (resets timer)
- 4Anyone can refresh (no signature needed if state preserved)
- 5Keep sufficient ERG reserves for multiple rent periods
- 6Design state to be recoverable if box is collected
Code Examples
{
// State box that anyone can refresh
val stateNFT = SELF.tokens(0)._1 // Unique identifier
val stateData = SELF.R4[Coll[Byte]].get
val lastRefresh = SELF.R5[Int].get
// Minimum ERG to survive rent (conservative estimate)
val minRentReserve = 10000000L // 0.01 ERG
// State operations by owner
val ownerPK = SELF.R6[SigmaProp].get
val ownerUpdate = {
val newState = OUTPUTS(0)
newState.tokens(0)._1 == stateNFT &&
newState.value >= minRentReserve &&
ownerPK
}
// Anyone can refresh (preserves state, resets rent timer)
val anyoneRefresh = {
val refreshedBox = OUTPUTS(0)
// State must be preserved exactly
val statePreserved =
refreshedBox.tokens(0)._1 == stateNFT &&
refreshedBox.R4[Coll[Byte]].get == stateData &&
refreshedBox.R6[SigmaProp].get == ownerPK &&
refreshedBox.propositionBytes == SELF.propositionBytes
// Value must be maintained or increased
val valueOk = refreshedBox.value >= SELF.value
// Update refresh timestamp
val timestampUpdated = refreshedBox.R5[Int].get == HEIGHT
statePreserved && valueOk && timestampUpdated
}
ownerUpdate || anyoneRefresh
}State box that anyone can refresh without owner's signature. Preserves state exactly while resetting rent timer.
Use Cases
- →Long-lived protocol state
- →DAO treasuries and governance
- →Oracle pool boxes
- →DEX liquidity pools
- →NFT collections with metadata
Security Considerations
- !Always keep sufficient ERG reserves
- !Design state to be recoverable if collected
- !Consider community-run refresh services
- !Monitor box ages and refresh proactively
- !Test rent scenarios on testnet
Resources
Fee Considerations
Refresh transactions cost standard fees. Budget for periodic refreshes (~1 per year minimum).