solana/core/src/cost_model.rs

//! 'cost_model` provides service to estimate a transaction's cost
//! It does so by analyzing accounts the transaction touches, and instructions
//! it includes. Using historical data as guideline, it estimates cost of
//! reading/writing account, the sum of that comes up to "account access cost";
//! Instructions take time to execute, both historical and runtime data are
//! used to determine each instruction's execution time, the sum of that
//! is transaction's "execution cost"
//! The main function is `calculate_cost` which returns a TransactionCost struct.
//!
use crate::execute_cost_table::ExecuteCostTable;
use log::*;
use solana_sdk::{message::Message, pubkey::Pubkey, transaction::Transaction};
use std::collections::HashMap;

// Guestimated from mainnet-beta data, sigver averages 1us, read averages 7us and write avergae 25us
const SIGNED_WRITABLE_ACCOUNT_ACCESS_COST: u64 = 1 + 25;
const SIGNED_READONLY_ACCOUNT_ACCESS_COST: u64 = 1 + 7;
const NON_SIGNED_WRITABLE_ACCOUNT_ACCESS_COST: u64 = 25;
const NON_SIGNED_READONLY_ACCOUNT_ACCESS_COST: u64 = 7;

// Sampled from mainnet-beta, the instruction execution timings stats are (in us):
// min=194, max=62164, avg=8214.49, med=2243
pub const ACCOUNT_MAX_COST: u64 = 100_000_000;
pub const BLOCK_MAX_COST: u64 = 2_500_000_000;

// cost of transaction is made of account_access_cost and instruction execution_cost
// where
// account_access_cost is the sum of read/write/sign all accounts included in the transaction
//     read is cheaper than write.
// execution_cost is the sum of all instructions execution cost, which is
//     observed during runtime and feedback by Replay
#[derive(Default, Debug)]
pub struct TransactionCost {
    pub writable_accounts: Vec<Pubkey>,
    pub account_access_cost: u64,
    pub execution_cost: u64,
}

#[derive(Debug)]
pub struct CostModel {
    account_cost_limit: u64,
    block_cost_limit: u64,
    instruction_execution_cost_table: ExecuteCostTable,
}

impl Default for CostModel {
    fn default() -> Self {
        CostModel::new(ACCOUNT_MAX_COST, BLOCK_MAX_COST)
    }
}

impl CostModel {
    pub fn new(chain_max: u64, block_max: u64) -> Self {
        Self {
            account_cost_limit: chain_max,
            block_cost_limit: block_max,
            instruction_execution_cost_table: ExecuteCostTable::default(),
        }
    }

    pub fn get_account_cost_limit(&self) -> u64 {
        self.account_cost_limit
    }

    pub fn get_block_cost_limit(&self) -> u64 {
        self.block_cost_limit
    }

    pub fn calculate_cost(&self, transaction: &Transaction) -> TransactionCost {
        let (
            signed_writable_accounts,
            signed_readonly_accounts,
            non_signed_writable_accounts,
            non_signed_readonly_accounts,
        ) = CostModel::sort_accounts_by_type(transaction.message());

        let mut cost = TransactionCost {
            writable_accounts: vec![],
            account_access_cost: CostModel::find_account_access_cost(
                &signed_writable_accounts,
                &signed_readonly_accounts,
                &non_signed_writable_accounts,
                &non_signed_readonly_accounts,
            ),
            execution_cost: self.find_transaction_cost(&transaction),
        };
        cost.writable_accounts.extend(&signed_writable_accounts);
        cost.writable_accounts.extend(&non_signed_writable_accounts);
        debug!("transaction {:?} has cost {:?}", transaction, cost);
        cost
    }

    // To update or insert instruction cost to table.
    pub fn upsert_instruction_cost(
        &mut self,
        program_key: &Pubkey,
        cost: &u64,
    ) -> Result<u64, &'static str> {
        self.instruction_execution_cost_table
            .upsert(program_key, cost);
        match self.instruction_execution_cost_table.get_cost(program_key) {
            Some(cost) => Ok(*cost),
            None => Err("failed to upsert to ExecuteCostTable"),
        }
    }

    pub fn get_instruction_cost_table(&self) -> &HashMap<Pubkey, u64> {
        self.instruction_execution_cost_table.get_cost_table()
    }

    fn find_instruction_cost(&self, program_key: &Pubkey) -> u64 {
        match self.instruction_execution_cost_table.get_cost(&program_key) {
            Some(cost) => *cost,
            None => {
                let default_value = self.instruction_execution_cost_table.get_mode();
                debug!(
                    "Program key {:?} does not have assigned cost, using mode {}",
                    program_key, default_value
                );
                default_value
            }
        }
    }

    fn find_transaction_cost(&self, transaction: &Transaction) -> u64 {
        let mut cost: u64 = 0;

        for instruction in &transaction.message().instructions {
            let program_id =
                transaction.message().account_keys[instruction.program_id_index as usize];
            let instruction_cost = self.find_instruction_cost(&program_id);
            trace!(
                "instruction {:?} has cost of {}",
                instruction,
                instruction_cost
            );
            cost += instruction_cost;
        }
        cost
    }

    fn find_account_access_cost(
        signed_writable_accounts: &[Pubkey],
        signed_readonly_accounts: &[Pubkey],
        non_signed_writable_accounts: &[Pubkey],
        non_signed_readonly_accounts: &[Pubkey],
    ) -> u64 {
        let mut cost = 0;
        cost += signed_writable_accounts.len() as u64 * SIGNED_WRITABLE_ACCOUNT_ACCESS_COST;
        cost += signed_readonly_accounts.len() as u64 * SIGNED_READONLY_ACCOUNT_ACCESS_COST;
        cost += non_signed_writable_accounts.len() as u64 * NON_SIGNED_WRITABLE_ACCOUNT_ACCESS_COST;
        cost += non_signed_readonly_accounts.len() as u64 * NON_SIGNED_READONLY_ACCOUNT_ACCESS_COST;
        cost
    }

    fn sort_accounts_by_type(
        message: &Message,
    ) -> (Vec<Pubkey>, Vec<Pubkey>, Vec<Pubkey>, Vec<Pubkey>) {
        let demote_sysvar_write_locks = true;
        let mut signer_writable: Vec<Pubkey> = vec![];
        let mut signer_readonly: Vec<Pubkey> = vec![];
        let mut non_signer_writable: Vec<Pubkey> = vec![];
        let mut non_signer_readonly: Vec<Pubkey> = vec![];
        message.account_keys.iter().enumerate().for_each(|(i, k)| {
            let is_signer = message.is_signer(i);
            let is_writable = message.is_writable(i, demote_sysvar_write_locks);

            if is_signer && is_writable {
                signer_writable.push(*k);
            } else if is_signer && !is_writable {
                signer_readonly.push(*k);
            } else if !is_signer && is_writable {
                non_signer_writable.push(*k);
            } else {
                non_signer_readonly.push(*k);
            }
        });
        (
            signer_writable,
            signer_readonly,
            non_signer_writable,
            non_signer_readonly,
        )
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use solana_runtime::{
        bank::Bank,
        genesis_utils::{create_genesis_config, GenesisConfigInfo},
    };
    use solana_sdk::{
        bpf_loader,
        hash::Hash,
        instruction::CompiledInstruction,
        message::Message,
        signature::{Keypair, Signer},
        system_instruction::{self},
        system_program, system_transaction,
    };
    use std::{
        str::FromStr,
        sync::{Arc, RwLock},
        thread::{self, JoinHandle},
    };

    fn test_setup() -> (Keypair, Hash) {
        solana_logger::setup();
        let GenesisConfigInfo {
            genesis_config,
            mint_keypair,
            ..
        } = create_genesis_config(10);
        let bank = Arc::new(Bank::new_no_wallclock_throttle(&genesis_config));
        let start_hash = bank.last_blockhash();
        (mint_keypair, start_hash)
    }

    #[test]
    fn test_cost_model_instruction_cost() {
        let mut testee = CostModel::default();

        let known_key = Pubkey::from_str("known11111111111111111111111111111111111111").unwrap();
        testee.upsert_instruction_cost(&known_key, &100).unwrap();
        // find cost for known programs
        assert_eq!(100, testee.find_instruction_cost(&known_key));

        testee
            .upsert_instruction_cost(&bpf_loader::id(), &1999)
            .unwrap();
        assert_eq!(1999, testee.find_instruction_cost(&bpf_loader::id()));

        // unknown program is assigned with default cost
        assert_eq!(
            testee.instruction_execution_cost_table.get_mode(),
            testee.find_instruction_cost(
                &Pubkey::from_str("unknown111111111111111111111111111111111111").unwrap()
            )
        );
    }

    #[test]
    fn test_cost_model_simple_transaction() {
        let (mint_keypair, start_hash) = test_setup();

        let keypair = Keypair::new();
        let simple_transaction =
            system_transaction::transfer(&mint_keypair, &keypair.pubkey(), 2, start_hash);
        debug!(
            "system_transaction simple_transaction {:?}",
            simple_transaction
        );

        // expected cost for one system transfer instructions
        let expected_cost = 8;

        let mut testee = CostModel::default();
        testee
            .upsert_instruction_cost(&system_program::id(), &expected_cost)
            .unwrap();
        assert_eq!(
            expected_cost,
            testee.find_transaction_cost(&simple_transaction)
        );
    }

    #[test]
    fn test_cost_model_transaction_many_transfer_instructions() {
        let (mint_keypair, start_hash) = test_setup();

        let key1 = solana_sdk::pubkey::new_rand();
        let key2 = solana_sdk::pubkey::new_rand();
        let instructions =
            system_instruction::transfer_many(&mint_keypair.pubkey(), &[(key1, 1), (key2, 1)]);
        let message = Message::new(&instructions, Some(&mint_keypair.pubkey()));
        let tx = Transaction::new(&[&mint_keypair], message, start_hash);
        debug!("many transfer transaction {:?}", tx);

        // expected cost for two system transfer instructions
        let program_cost = 8;
        let expected_cost = program_cost * 2;

        let mut testee = CostModel::default();
        testee
            .upsert_instruction_cost(&system_program::id(), &program_cost)
            .unwrap();
        assert_eq!(expected_cost, testee.find_transaction_cost(&tx));
    }

    #[test]
    fn test_cost_model_message_many_different_instructions() {
        let (mint_keypair, start_hash) = test_setup();

        // construct a transaction with multiple random instructions
        let key1 = solana_sdk::pubkey::new_rand();
        let key2 = solana_sdk::pubkey::new_rand();
        let prog1 = solana_sdk::pubkey::new_rand();
        let prog2 = solana_sdk::pubkey::new_rand();
        let instructions = vec![
            CompiledInstruction::new(3, &(), vec![0, 1]),
            CompiledInstruction::new(4, &(), vec![0, 2]),
        ];
        let tx = Transaction::new_with_compiled_instructions(
            &[&mint_keypair],
            &[key1, key2],
            start_hash,
            vec![prog1, prog2],
            instructions,
        );
        debug!("many random transaction {:?}", tx);

        let testee = CostModel::default();
        let result = testee.find_transaction_cost(&tx);

        // expected cost for two random/unknown program is
        let expected_cost = testee.instruction_execution_cost_table.get_mode() * 2;
        assert_eq!(expected_cost, result);
    }

    #[test]
    fn test_cost_model_sort_message_accounts_by_type() {
        // construct a transaction with two random instructions with same signer
        let signer1 = Keypair::new();
        let signer2 = Keypair::new();
        let key1 = Pubkey::new_unique();
        let key2 = Pubkey::new_unique();
        let prog1 = Pubkey::new_unique();
        let prog2 = Pubkey::new_unique();
        let instructions = vec![
            CompiledInstruction::new(4, &(), vec![0, 2]),
            CompiledInstruction::new(5, &(), vec![1, 3]),
        ];
        let tx = Transaction::new_with_compiled_instructions(
            &[&signer1, &signer2],
            &[key1, key2],
            Hash::new_unique(),
            vec![prog1, prog2],
            instructions,
        );
        debug!("many random transaction {:?}", tx);

        let (
            signed_writable_accounts,
            signed_readonly_accounts,
            non_signed_writable_accounts,
            non_signed_readonly_accounts,
        ) = CostModel::sort_accounts_by_type(tx.message());

        assert_eq!(2, signed_writable_accounts.len());
        assert_eq!(signer1.pubkey(), signed_writable_accounts[0]);
        assert_eq!(signer2.pubkey(), signed_writable_accounts[1]);
        assert_eq!(0, signed_readonly_accounts.len());
        assert_eq!(2, non_signed_writable_accounts.len());
        assert_eq!(key1, non_signed_writable_accounts[0]);
        assert_eq!(key2, non_signed_writable_accounts[1]);
        assert_eq!(2, non_signed_readonly_accounts.len());
        assert_eq!(prog1, non_signed_readonly_accounts[0]);
        assert_eq!(prog2, non_signed_readonly_accounts[1]);
    }

    #[test]
    fn test_cost_model_insert_instruction_cost() {
        let key1 = Pubkey::new_unique();
        let cost1 = 100;

        let mut cost_model = CostModel::default();
        // Using default cost for unknown instruction
        assert_eq!(
            cost_model.instruction_execution_cost_table.get_mode(),
            cost_model.find_instruction_cost(&key1)
        );

        // insert instruction cost to table
        assert!(cost_model.upsert_instruction_cost(&key1, &cost1).is_ok());

        // now it is known insturction with known cost
        assert_eq!(cost1, cost_model.find_instruction_cost(&key1));
    }

    #[test]
    fn test_cost_model_calculate_cost() {
        let (mint_keypair, start_hash) = test_setup();
        let tx =
            system_transaction::transfer(&mint_keypair, &Keypair::new().pubkey(), 2, start_hash);

        let expected_account_cost = SIGNED_WRITABLE_ACCOUNT_ACCESS_COST
            + NON_SIGNED_WRITABLE_ACCOUNT_ACCESS_COST
            + NON_SIGNED_READONLY_ACCOUNT_ACCESS_COST;
        let expected_execution_cost = 8;

        let mut cost_model = CostModel::default();
        cost_model
            .upsert_instruction_cost(&system_program::id(), &expected_execution_cost)
            .unwrap();
        let tx_cost = cost_model.calculate_cost(&tx);
        assert_eq!(expected_account_cost, tx_cost.account_access_cost);
        assert_eq!(expected_execution_cost, tx_cost.execution_cost);
        assert_eq!(2, tx_cost.writable_accounts.len());
    }

    #[test]
    fn test_cost_model_update_instruction_cost() {
        let key1 = Pubkey::new_unique();
        let cost1 = 100;
        let cost2 = 200;
        let updated_cost = (cost1 + cost2) / 2;

        let mut cost_model = CostModel::default();

        // insert instruction cost to table
        assert!(cost_model.upsert_instruction_cost(&key1, &cost1).is_ok());
        assert_eq!(cost1, cost_model.find_instruction_cost(&key1));

        // update instruction cost
        assert!(cost_model.upsert_instruction_cost(&key1, &cost2).is_ok());
        assert_eq!(updated_cost, cost_model.find_instruction_cost(&key1));
    }

    #[test]
    fn test_cost_model_can_be_shared_concurrently_as_immutable() {
        let (mint_keypair, start_hash) = test_setup();
        let number_threads = 10;
        let expected_account_cost = SIGNED_WRITABLE_ACCOUNT_ACCESS_COST
            + NON_SIGNED_WRITABLE_ACCOUNT_ACCESS_COST
            + NON_SIGNED_READONLY_ACCOUNT_ACCESS_COST;

        let cost_model = Arc::new(CostModel::default());

        let thread_handlers: Vec<JoinHandle<()>> = (0..number_threads)
            .map(|_| {
                // each thread creates its own simple transaction
                let simple_transaction = system_transaction::transfer(
                    &mint_keypair,
                    &Keypair::new().pubkey(),
                    2,
                    start_hash,
                );
                let cost_model = cost_model.clone();
                thread::spawn(move || {
                    let tx_cost = cost_model.calculate_cost(&simple_transaction);
                    assert_eq!(2, tx_cost.writable_accounts.len());
                    assert_eq!(expected_account_cost, tx_cost.account_access_cost);
                    assert_eq!(
                        cost_model.instruction_execution_cost_table.get_mode(),
                        tx_cost.execution_cost
                    );
                })
            })
            .collect();

        for th in thread_handlers {
            th.join().unwrap();
        }
    }

    #[test]
    fn test_cost_model_can_be_shared_concurrently_with_rwlock() {
        let (mint_keypair, start_hash) = test_setup();
        // construct a transaction with multiple random instructions
        let key1 = solana_sdk::pubkey::new_rand();
        let key2 = solana_sdk::pubkey::new_rand();
        let prog1 = solana_sdk::pubkey::new_rand();
        let prog2 = solana_sdk::pubkey::new_rand();
        let instructions = vec![
            CompiledInstruction::new(3, &(), vec![0, 1]),
            CompiledInstruction::new(4, &(), vec![0, 2]),
        ];
        let tx = Arc::new(Transaction::new_with_compiled_instructions(
            &[&mint_keypair],
            &[key1, key2],
            start_hash,
            vec![prog1, prog2],
            instructions,
        ));

        let number_threads = 10;
        let expected_account_cost = SIGNED_WRITABLE_ACCOUNT_ACCESS_COST
            + NON_SIGNED_WRITABLE_ACCOUNT_ACCESS_COST * 2
            + NON_SIGNED_READONLY_ACCOUNT_ACCESS_COST * 2;
        let cost1 = 100;
        let cost2 = 200;
        // execution cost can be either 2 * Default (before write) or cost1+cost2 (after write)

        let cost_model: Arc<RwLock<CostModel>> = Arc::new(RwLock::new(CostModel::default()));

        let thread_handlers: Vec<JoinHandle<()>> = (0..number_threads)
            .map(|i| {
                let cost_model = cost_model.clone();
                let tx = tx.clone();

                if i == 5 {
                    thread::spawn(move || {
                        let mut cost_model = cost_model.write().unwrap();
                        assert!(cost_model.upsert_instruction_cost(&prog1, &cost1).is_ok());
                        assert!(cost_model.upsert_instruction_cost(&prog2, &cost2).is_ok());
                    })
                } else {
                    thread::spawn(move || {
                        let tx_cost = cost_model.read().unwrap().calculate_cost(&tx);
                        assert_eq!(3, tx_cost.writable_accounts.len());
                        assert_eq!(expected_account_cost, tx_cost.account_access_cost);
                    })
                }
            })
            .collect();

        for th in thread_handlers {
            th.join().unwrap();
        }
    }
}