How to store 10KB+ data in a Solana Account?

Question

I am trying to store 100KB+ data on a Solana Account. In Solana documents I've read that

"The current maximum size of an account's data is 10 megabytes."

Source: https://docs.solana.com/developing/programming-model/accounts

But when I try to create a space more than 10KB (space = 10240) it gives me error during init tests:

"Error processing Instruction 0: Failed to reallocate account data"

Here is an example code:

#[derive(Accounts)]
pub struct Initialize<'info> {
    #[account(init, payer = user, space=100000)] 
     pub example_account: Account<'info, ExampleAccount>,

    #[account(mut)]
    pub user: Signer<'info>,
    pub system_program: Program<'info, System>
}

#[account]
pub struct ExampleAccount {
    pub data: String,
}

I need to store 100KB data on that account. How can I do that?

Answer 1

While the maximum account size is 10 megabytes, the maximum permitted size of a reallocation in an inner instruction is 10240 bytes. Anchor has to make a CPI to allocate the space for your account, so the maximum space it can allocate is 10240 bytes. If you want to store more than that, you will have to pass in an account you have created with a separate createAccount instruction.

If you are not initializing the account with a CPI, you would instead do:

#[account(zero)] 
pub example_account: Account<'info, ExampleAccount>,

And then when you call Initialize:

const create_account_instruction = SystemProgram.createAccount({
    fromPubkey: user,
    newAccountPubkey: exampleAccountKey,
    space: 100000,
    lamports,
    programId: yourProgramId
});
const your_instruction = program.instruction.initialize({ 
    accounts: { 
        exampleAccount: exampleAccountKey,
        user: user,
        systemProgram: systemProgramId
    }
});
const txn = new Transaction().add(create_account_instruction, your_instruction);

Answer 2

It is possible to allocate a PDA with up to 10 MiB. Use the init instruction to allocate 10240 bytes, this is the maximum that is allowed to be allocated through a CPI. Then you can execute another instruction that calls AccountInfo::realloc for every additional 10240 bytes that you need in the account. You can group many of these together in a single transaction. Ensure you have sufficient lamports in the account before reallocating.

The other approach, described in Ellen High's answer, is to initialize an account from a new keypair that signs a transaction containing a transaction-level instruction to the system program to initialize the account up to 10 MiB, plus an instruction that transfers ownership to the program (which can be tx-level or a CPI). But often it is preferable to use a PDA.