Programming Model

Storing and Accounts

In EVM-based languages, we store the on-chain data in the smart contract fields but in Solana it is different. In Solana, we use accounts to store on-chain data. Each account has 32 Bytes (256 bits) address to identify.

Types of Accounts in Solana:

  • Program Account: These accounts execute code on-chain. They are also known as Solana programs. A program is the owner of all accounts. The owner of a program is another program called system program. This program creates new accounts (all three types), allocation account data, ownership assignment and rent related task.

  • Storage Account: These accounts function like separate files with a shared structure defined by a Solana program. They store the data or state of a program and can include metadata such as access restrictions.

  • Token Account: These accounts track the balances of tokens and allow for the transfer of tokens.

System Program (parent) (type of program account)
                          || 
                          || create and manage
                          ||
program account (child) - storage account - token account

Accounts Communication On-Chain

On Solana, the program account, the storage account and the token account are completely separate on–chain entities, so you need a defined way to pass data back and forth.

How do these entities connect to each other in a transaction?

  1. The client (JS/TS) builds an instruction specifying:
    • The program’s public key (so Solana knows which code to run).
    • A list of accounts (including your storage account).
    • Any serialized instruction data (e.g. the u64 for set).
  2. Solana loads your program account’s code, plus the raw byte buffers of each listed account.
  3. Anchor’s generated entrypoint:
    • Deserializes each account buffer into the structs you declared in your Context<…>.
    • Calls your handler function (initialize, increase, etc.).
    • Serializes any modified structs back into the raw account buffers.
  4. Modified bytes persist in the storage account’s data field.
program account             storage account
(address123)                (address456)
       ||                          ||
       ||                          ||
       ||                          ||
  Communication with serialization and deserialization.
  DApp needs to know both address for both accounts.

Rent

Stroing data in Solana is not free of charge. When we create a new account on Solana, we need to pay rent to keep the data stored on the network. The unit of the rent is lamports (1,000,000,000 lamports = 1 SOL). If an account runs out of rent, it will delete from the network with its own data.

Rent Exemption: It means that if an account holds at least two years of rent, it will not remove from the network. All the accounts that create with default mechanism should me rent-exempt

Calculate Rent

If we want to create an account holding 32 bytes of data, we can calculate the rent with this command:

solana rent 64

# Output
# Rent per byte-year: 0.00000689 SOL
# Rent per epoch: 0.000003158 SOL
# Rent-exempt minimum: 0.0042158 SOL

To be rent-exempt, you need to pay at least 0.0011136 SOL.

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