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Overview

Persistent storage is designed for data that must remain available indefinitely and be recoverable after expiration. Access persistent storage via env.storage().persistent(). Key Properties:
  • More expensive than temporary storage
  • Expired entries move to Expired State Stack (ESS) for recovery
  • Only one version can exist at a time (cannot recreate while expired version exists)
  • Best for critical data: token balances, ownership records, user profiles

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Type Definition

pub struct Persistent {
    storage: Storage,
}
Access through the Storage type: 
let persistent = env.storage().persistent();

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Methods

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has

Checks if a value exists for the given key. 
pub fn has<K>(&self, key: &K) -> bool
where
    K: IntoVal<Env, Val>,
Parameters:
  • key: The key to check
Returns: true if a value exists, false otherwise Example: 
use soroban_sdk::{contract, contractimpl, Env, symbol_short};

#[contract]
pub struct Contract;

#[contractimpl]
impl Contract {
    pub fn check_balance(env: Env, user: Address) -> bool {
        let key = symbol_short!("balance");
        env.storage().persistent().has(&key)
    }
}

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get

Retrieves a value for the given key. 
pub fn get<K, V>(&self, key: &K) -> Option<V>
where
    V::Error: Debug,
    K: IntoVal<Env, Val>,
    V: TryFromVal<Env, Val>,
Parameters:
  • key: The key to retrieve
Returns: Some(V) if the value exists, None otherwise Panics: If the stored value cannot be converted to type V Example: 
use soroban_sdk::{contract, contractimpl, Env, Address, symbol_short};

#[contract]
pub struct TokenContract;

#[contractimpl]
impl TokenContract {
    pub fn get_balance(env: Env, user: Address) -> i128 {
        let key = symbol_short!("balance");
        env.storage()
            .persistent()
            .get::<_, i128>(&key)
            .unwrap_or(0)
    }
}

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set

Stores a value for the given key. 
pub fn set<K, V>(&self, key: &K, val: &V)
where
    K: IntoVal<Env, Val>,
    V: IntoVal<Env, Val>,
Parameters:
  • key: The key to store under
  • val: The value to store
Example: 
use soroban_sdk::{contract, contractimpl, Env, Address, symbol_short};

#[contract]
pub struct TokenContract;

#[contractimpl]
impl TokenContract {
    pub fn set_balance(env: Env, user: Address, amount: i128) {
        let key = symbol_short!("balance");
        env.storage().persistent().set(&key, &amount);
        
        // Extend TTL to ensure balance persists
        env.storage().persistent().extend_ttl(&key, 100, 1000);
    }
}

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update

Updates a value by applying a function to the current value. 
pub fn update<K, V>(&self, key: &K, f: impl FnOnce(Option<V>) -> V) -> V
where
    K: IntoVal<Env, Val>,
    V: IntoVal<Env, Val>,
    V: TryFromVal<Env, Val>,
Parameters:
  • key: The key to update
  • f: Function that receives current value (or None) and returns new value
Returns: The new value after update Example: 
use soroban_sdk::{contract, contractimpl, Env, Address, symbol_short};

#[contract]
pub struct Counter;

#[contractimpl]
impl Counter {
    pub fn increment(env: Env) -> u32 {
        let key = symbol_short!("count");
        env.storage().persistent().update(&key, |count: Option<u32>| {
            count.unwrap_or(0) + 1
        })
    }
}

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try_update

Updates a value by applying a fallible function. 
pub fn try_update<K, V, E>(
    &self,
    key: &K,
    f: impl FnOnce(Option<V>) -> Result<V, E>,
) -> Result<V, E>
where
    K: IntoVal<Env, Val>,
    V: IntoVal<Env, Val>,
    V: TryFromVal<Env, Val>,
Parameters:
  • key: The key to update
  • f: Fallible function that receives current value and returns Result<V, E>
Returns: Ok(V) with the new value, or Err(E) if the function fails Example: 
use soroban_sdk::{contract, contractimpl, contracterror, Env, Address, symbol_short};

#[contracterror]
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum Error {
    InsufficientBalance = 1,
}

#[contract]
pub struct TokenContract;

#[contractimpl]
impl TokenContract {
    pub fn transfer(env: Env, from: Address, amount: i128) -> Result<(), Error> {
        let key = symbol_short!("balance");
        env.storage().persistent().try_update(&key, |balance: Option<i128>| {
            let current = balance.unwrap_or(0);
            if current < amount {
                Err(Error::InsufficientBalance)
            } else {
                Ok(current - amount)
            }
        })?;
        Ok(())
    }
}

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extend_ttl

Extends the time-to-live for a storage entry. 
pub fn extend_ttl<K>(&self, key: &K, threshold: u32, extend_to: u32)
where
    K: IntoVal<Env, Val>,
Parameters:
  • key: The storage key to extend
  • threshold: Only extend if TTL is below this value (in ledgers)
  • extend_to: New TTL value when extended (in ledgers)
Behavior:
  • Only extends TTL if current TTL < threshold
  • Sets TTL to extend_to ledgers from current ledger
  • No-op if TTL >= threshold (prevents unnecessary operations)
Example: 
use soroban_sdk::{contract, contractimpl, Env, Address, symbol_short};

#[contract]
pub struct TokenContract;

#[contractimpl]
impl TokenContract {
    pub fn bump_balance(env: Env, user: Address) {
        let key = symbol_short!("balance");
        
        // Extend if TTL drops below 100 ledgers
        // Extend to 1000 ledgers when triggered
        env.storage().persistent().extend_ttl(&key, 100, 1000);
    }
    
    pub fn transfer(env: Env, from: Address, to: Address, amount: i128) {
        // Extend TTL on every access
        let from_key = symbol_short!("from_bal");
        let to_key = symbol_short!("to_bal");
        
        env.storage().persistent().extend_ttl(&from_key, 100, 1000);
        env.storage().persistent().extend_ttl(&to_key, 100, 1000);
        
        // ... transfer logic
    }
}
Best Practices:
  • Set threshold to allow time for extension before expiration
  • Set extend_to considering access patterns and costs
  • Extend TTL on every write or read for critical data
  • Use higher extend_to values for frequently accessed data

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remove

Removes a key and its value from storage. 
pub fn remove<K>(&self, key: &K)
where
    K: IntoVal<Env, Val>,
Parameters:
  • key: The key to remove
Behavior: No-op if the key doesn’t exist Example: 
use soroban_sdk::{contract, contractimpl, Env, Address, symbol_short};

#[contract]
pub struct Contract;

#[contractimpl]
impl Contract {
    pub fn close_account(env: Env, user: Address) {
        let key = symbol_short!("balance");
        env.storage().persistent().remove(&key);
    }
}

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Complete Example

Here’s a complete token contract demonstrating persistent storage usage: 
use soroban_sdk::{
    contract, contractimpl, contracterror, Env, Address, symbol_short
};

#[contracterror]
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub enum Error {
    InsufficientBalance = 1,
}

#[contract]
pub struct TokenContract;

#[contractimpl]
impl TokenContract {
    pub fn transfer(
        env: Env,
        from: Address,
        to: Address,
        amount: i128,
    ) -> Result<(), Error> {
        from.require_auth();
        
        let storage = env.storage().persistent();
        
        // Deduct from sender
        let from_key = symbol_short!("from_bal");
        let new_from_balance = storage.try_update(&from_key, |balance: Option<i128>| {
            let current = balance.unwrap_or(0);
            if current < amount {
                Err(Error::InsufficientBalance)
            } else {
                Ok(current - amount)
            }
        })?;
        
        // Add to receiver
        let to_key = symbol_short!("to_bal");
        storage.update(&to_key, |balance: Option<i128>| {
            balance.unwrap_or(0) + amount
        });
        
        // Extend TTL for both accounts
        // Extend if TTL < 100 ledgers, set to 1000 ledgers
        storage.extend_ttl(&from_key, 100, 1000);
        storage.extend_ttl(&to_key, 100, 1000);
        
        Ok(())
    }
    
    pub fn balance(env: Env, account: Address) -> i128 {
        let key = symbol_short!("balance");
        env.storage()
            .persistent()
            .get(&key)
            .unwrap_or(0)
    }
}

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Test Utilities

When the testutils feature is enabled, additional methods are available: 
#[cfg(test)]
mod test {
    use soroban_sdk::{Env, symbol_short, testutils::storage::Persistent};
    
    #[test]
    fn test_storage() {
        let env = Env::default();
        let storage = env.storage().persistent();
        
        // Get all persistent storage entries
        let all_data = storage.all();
        
        // Get TTL for a specific key
        let key = symbol_short!("balance");
        let ttl = storage.get_ttl(&key);
        
        assert!(ttl > 0);
    }
}

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See Also

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Source Reference

Implementation: soroban-sdk/src/storage.rs:301-388

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