Function attach_bal_before_tx 

pub fn attach_bal_before_tx<DB>(
    db: &mut State<DB>,
    bal: &DecodedBal<Arc<Bal>>,
    tx_index: usize,
)
where
    DB: Database,

Available on crate feature rpc only.

Attaches bal to the database, positioned at the state right before the transaction at tx_index.

Reads served by the attached BAL reflect all writes prior to the transaction, including the block’s pre-execution system calls. Reads not covered by the BAL fall back to the underlying database, which holds the correct values for all state the block does not touch.

Note: changes must not be committed to the database afterwards, because the attached BAL takes precedence over committed state when serving reads.