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How to Change Account Size on Solana

Accounts are a key part of developing on Solana. For the longest time accounts were static in size and the only way to change their size was to create a new account. Your entire dApp architecture chained down by the fact that you cannot change your account size.

Now you can dynamically change the size of your accounts.

Realloc

The Realloc feature was enabled since slot 133920008, or May 15th, 2022.

realloc is a new method on the AccountInfo struct that allows you to set a new size for an account.

The realloc method:

pub fn realloc(
    &self,
    new_len: usize,
    zero_init: bool
) -> Result<(), ProgramError>
  • new_len is defined as the new size in bytes
  • zero_init is used to zero out new bytes if the account is resized smaller then larger again in the same instruction.

Limitations:

  • Realloc can only be used on Program owned accounts
  • Max increase in bytes per call is 10KB

How to use Realloc

When you change the size of an account you must also make sure the account is still rent-exempt. Before the change, you can calculate the new rent requirements and fund the account.

let new_size = pda_account.data.borrow().len() + 32;
let rent = Rent::get()?;
let new_minimum_balance = rent.minimum_balance(new_size);

let lamports_diff = new_minimum_balance.saturating_sub(pda_account.lamports());
invoke(
    &system_instruction::transfer(funding_account.key, pda_account.key, lamports_diff),
    &[
        funding_account.clone(),
        pda_account.clone(),
        system_program.clone(),
    ],
)?;

Once you guarantee that the account achieves the rent-exempt status with the new account size, you can realloc the account.

pda_account.realloc(new_size, false)?;

That's it!

Running this example

To run this example, you need to run the following commands:

# In /program
$ cargo build-bpf
$ solana program deploy <PROGRAM OUTPUT>.so

# In /js
$ yarn && yarn run test

Use Cases

Dynamically changing the size of an account opens up the door to a ton of new use cases.

You can:

  • Dynamically increase the size of a list
  • Migrate accounts on program upgrade
  • Allow users to pay their way for space

and much more!