Zero-Copy Accounts

Zero-copy accounts use bytemuck layout and AccountLoader to avoid Borsh serialize/deserialize on large structs, saving CU for big state.

Recipe

#[account(zero_copy)]
pub struct Market {
    pub bids: [u64; 1024],
}
 
#[derive(Accounts)]
pub struct Update<'info> {
    #[account(mut)]
    pub market: AccountLoader<'info, Market>,
}

When to reach for this: Account data is large (order books, tick arrays) and Borsh costs too much CU.

Working Example

use anchor_lang::prelude::*;
 
#[account(zero_copy)]
#[repr(C)]
pub struct LargeState {
    pub head: u64,
    pub data: [u8; 10_000],
}
 
pub fn touch(ctx: Context<Touch>) -> Result<()> {
    let mut market = ctx.accounts.state.load_mut()?;
    market.head += 1;
    Ok(())
}
 
#[derive(Accounts)]
pub struct Touch<'info> {
    #[account(mut)]
    pub state: AccountLoader<'info, LargeState>,
}

What this demonstrates:

• zero_copy requires repr(C) layout
• AccountLoader::load_mut for mutation
• No INIT_SPACE Borsh sizing same way
• Discriminator still applies

Deep Dive

Layout Discipline

• Fixed-size arrays only unless using careful manual management.
• Alignment matters; follow bytemuck rules.
• Migrations harder than Borsh accounts.

CU Win

Avoid full account memcpy on each instruction.

Gotchas

• Unaligned fields - Undefined behavior. Fix: Use repr(C) and bytemuck Pod.
• Mixing Borsh and zero_copy - Wrong loader type. Fix: Pick one per account.
• Dynamic Vec in zero_copy - Not supported naively. Fix: Fixed buffers or Borsh account.
• Forgot mut on loader account - Cannot persist. Fix: Mark account mut.
• Upgrade layout without migration - Corrupts account. Fix: Version and migrate.

Alternatives

FAQs

Related

• Zero-Copy Accounts - serialization view
• CU & Size Optimization - CU
• Custom Account Types - traits

Stack versions: This page was written for Agave 4.1.1, Solana CLI 3.0.10, Anchor 0.32.1, anchor-lang 0.32.1, Rust 1.91.1, @solana/kit 7.0.0, Surfpool 0.12.0, and LiteSVM 0.6.x.