solana/runtime/src/cost_tracker.rs

//! `cost_tracker` keeps tracking transaction cost per chained accounts as well as for entire block
//! The main functions are:
//! - would_transaction_fit(&tx_cost), immutable function to test if tx with tx_cost would fit into current block
//! - add_transaction_cost(&tx_cost), mutable function to accumulate tx_cost to tracker.
//!
use crate::block_cost_limits::*;
use crate::cost_model::TransactionCost;
use crate::cost_tracker_stats::CostTrackerStats;
use solana_sdk::{clock::Slot, pubkey::Pubkey, transaction::SanitizedTransaction};
use std::collections::HashMap;

const WRITABLE_ACCOUNTS_PER_BLOCK: usize = 512;

#[derive(Debug, Clone)]
pub enum CostTrackerError {
    /// would exceed block max limit
    WouldExceedBlockMaxLimit,

    /// would exceed account max limit
    WouldExceedAccountMaxLimit,
}

#[derive(AbiExample, Debug)]
pub struct CostTracker {
    account_cost_limit: u64,
    block_cost_limit: u64,
    current_bank_slot: Slot,
    cost_by_writable_accounts: HashMap<Pubkey, u64>,
    block_cost: u64,
}

impl Default for CostTracker {
    fn default() -> Self {
        CostTracker::new(MAX_WRITABLE_ACCOUNT_UNITS, MAX_BLOCK_UNITS)
    }
}

impl CostTracker {
    pub fn new(account_cost_limit: u64, block_cost_limit: u64) -> Self {
        assert!(account_cost_limit <= block_cost_limit);
        Self {
            account_cost_limit,
            block_cost_limit,
            current_bank_slot: 0,
            cost_by_writable_accounts: HashMap::with_capacity(WRITABLE_ACCOUNTS_PER_BLOCK),
            block_cost: 0,
        }
    }

    // bench tests needs to reset limits
    pub fn set_limits(&mut self, account_cost_limit: u64, block_cost_limit: u64) {
        self.account_cost_limit = account_cost_limit;
        self.block_cost_limit = block_cost_limit;
    }

    pub fn would_transaction_fit(
        &self,
        _transaction: &SanitizedTransaction,
        tx_cost: &TransactionCost,
        stats: &mut CostTrackerStats,
    ) -> Result<(), CostTrackerError> {
        self.would_fit(&tx_cost.writable_accounts, &tx_cost.sum(), stats)
    }

    pub fn add_transaction_cost(
        &mut self,
        _transaction: &SanitizedTransaction,
        tx_cost: &TransactionCost,
        stats: &mut CostTrackerStats,
    ) {
        let cost = tx_cost.sum();
        self.add_transaction(&tx_cost.writable_accounts, &cost);

        stats.transaction_count += 1;
        stats.block_cost += cost;
    }

    pub fn try_add(
        &mut self,
        _transaction: &SanitizedTransaction,
        tx_cost: &TransactionCost,
        stats: &mut CostTrackerStats,
    ) -> Result<u64, CostTrackerError> {
        let cost = tx_cost.sum();
        self.would_fit(&tx_cost.writable_accounts, &cost, stats)?;
        self.add_transaction(&tx_cost.writable_accounts, &cost);
        Ok(self.block_cost)
    }

    fn would_fit(
        &self,
        keys: &[Pubkey],
        cost: &u64,
        stats: &mut CostTrackerStats,
    ) -> Result<(), CostTrackerError> {
        stats.transaction_cost_histogram.increment(*cost).unwrap();

        // check against the total package cost
        if self.block_cost + cost > self.block_cost_limit {
            return Err(CostTrackerError::WouldExceedBlockMaxLimit);
        }

        // check if the transaction itself is more costly than the account_cost_limit
        if *cost > self.account_cost_limit {
            return Err(CostTrackerError::WouldExceedAccountMaxLimit);
        }

        // check each account against account_cost_limit,
        for account_key in keys.iter() {
            match self.cost_by_writable_accounts.get(account_key) {
                Some(chained_cost) => {
                    stats
                        .writable_accounts_cost_histogram
                        .increment(*chained_cost)
                        .unwrap();

                    if chained_cost + cost > self.account_cost_limit {
                        return Err(CostTrackerError::WouldExceedAccountMaxLimit);
                    } else {
                        continue;
                    }
                }
                None => continue,
            }
        }

        Ok(())
    }

    fn add_transaction(&mut self, keys: &[Pubkey], cost: &u64) {
        for account_key in keys.iter() {
            *self
                .cost_by_writable_accounts
                .entry(*account_key)
                .or_insert(0) += cost;
        }
        self.block_cost += cost;
    }
}

// CostStats can be collected by util, such as ledger_tool
#[derive(Default, Debug)]
pub struct CostStats {
    pub bank_slot: Slot,
    pub total_cost: u64,
    pub number_of_accounts: usize,
    pub costliest_account: Pubkey,
    pub costliest_account_cost: u64,
}

impl CostTracker {
    pub fn get_stats(&self) -> CostStats {
        let mut stats = CostStats {
            bank_slot: self.current_bank_slot,
            total_cost: self.block_cost,
            number_of_accounts: self.cost_by_writable_accounts.len(),
            costliest_account: Pubkey::default(),
            costliest_account_cost: 0,
        };

        for (key, cost) in self.cost_by_writable_accounts.iter() {
            if cost > &stats.costliest_account_cost {
                stats.costliest_account = *key;
                stats.costliest_account_cost = *cost;
            }
        }

        stats
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{
        bank::Bank,
        genesis_utils::{create_genesis_config, GenesisConfigInfo},
    };
    use solana_sdk::{
        hash::Hash,
        signature::{Keypair, Signer},
        system_transaction,
        transaction::Transaction,
    };
    use std::{cmp, convert::TryFrom, sync::Arc};

    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_for_tests(&genesis_config));
        let start_hash = bank.last_blockhash();
        (mint_keypair, start_hash)
    }

    fn build_simple_transaction(
        mint_keypair: &Keypair,
        start_hash: &Hash,
    ) -> (Transaction, Vec<Pubkey>, u64) {
        let keypair = Keypair::new();
        let simple_transaction =
            system_transaction::transfer(mint_keypair, &keypair.pubkey(), 2, *start_hash);

        (simple_transaction, vec![mint_keypair.pubkey()], 5)
    }

    #[test]
    fn test_cost_tracker_initialization() {
        let testee = CostTracker::new(10, 11);
        assert_eq!(10, testee.account_cost_limit);
        assert_eq!(11, testee.block_cost_limit);
        assert_eq!(0, testee.cost_by_writable_accounts.len());
        assert_eq!(0, testee.block_cost);
    }

    #[test]
    fn test_cost_tracker_ok_add_one() {
        let (mint_keypair, start_hash) = test_setup();
        let (_tx, keys, cost) = build_simple_transaction(&mint_keypair, &start_hash);

        // build testee to have capacity for one simple transaction
        let mut testee = CostTracker::new(cost, cost);
        assert!(testee
            .would_fit(&keys, &cost, &mut CostTrackerStats::default())
            .is_ok());
        testee.add_transaction(&keys, &cost);
        assert_eq!(cost, testee.block_cost);
    }

    #[test]
    fn test_cost_tracker_ok_add_two_same_accounts() {
        let (mint_keypair, start_hash) = test_setup();
        // build two transactions with same signed account
        let (_tx1, keys1, cost1) = build_simple_transaction(&mint_keypair, &start_hash);
        let (_tx2, keys2, cost2) = build_simple_transaction(&mint_keypair, &start_hash);

        // build testee to have capacity for two simple transactions, with same accounts
        let mut testee = CostTracker::new(cost1 + cost2, cost1 + cost2);
        {
            assert!(testee
                .would_fit(&keys1, &cost1, &mut CostTrackerStats::default())
                .is_ok());
            testee.add_transaction(&keys1, &cost1);
        }
        {
            assert!(testee
                .would_fit(&keys2, &cost2, &mut CostTrackerStats::default())
                .is_ok());
            testee.add_transaction(&keys2, &cost2);
        }
        assert_eq!(cost1 + cost2, testee.block_cost);
        assert_eq!(1, testee.cost_by_writable_accounts.len());
    }

    #[test]
    fn test_cost_tracker_ok_add_two_diff_accounts() {
        let (mint_keypair, start_hash) = test_setup();
        // build two transactions with diff accounts
        let (_tx1, keys1, cost1) = build_simple_transaction(&mint_keypair, &start_hash);
        let second_account = Keypair::new();
        let (_tx2, keys2, cost2) = build_simple_transaction(&second_account, &start_hash);

        // build testee to have capacity for two simple transactions, with same accounts
        let mut testee = CostTracker::new(cmp::max(cost1, cost2), cost1 + cost2);
        {
            assert!(testee
                .would_fit(&keys1, &cost1, &mut CostTrackerStats::default())
                .is_ok());
            testee.add_transaction(&keys1, &cost1);
        }
        {
            assert!(testee
                .would_fit(&keys2, &cost2, &mut CostTrackerStats::default())
                .is_ok());
            testee.add_transaction(&keys2, &cost2);
        }
        assert_eq!(cost1 + cost2, testee.block_cost);
        assert_eq!(2, testee.cost_by_writable_accounts.len());
    }

    #[test]
    fn test_cost_tracker_chain_reach_limit() {
        let (mint_keypair, start_hash) = test_setup();
        // build two transactions with same signed account
        let (_tx1, keys1, cost1) = build_simple_transaction(&mint_keypair, &start_hash);
        let (_tx2, keys2, cost2) = build_simple_transaction(&mint_keypair, &start_hash);

        // build testee to have capacity for two simple transactions, but not for same accounts
        let mut testee = CostTracker::new(cmp::min(cost1, cost2), cost1 + cost2);
        // should have room for first transaction
        {
            assert!(testee
                .would_fit(&keys1, &cost1, &mut CostTrackerStats::default())
                .is_ok());
            testee.add_transaction(&keys1, &cost1);
        }
        // but no more sapce on the same chain (same signer account)
        {
            assert!(testee
                .would_fit(&keys2, &cost2, &mut CostTrackerStats::default())
                .is_err());
        }
    }

    #[test]
    fn test_cost_tracker_reach_limit() {
        let (mint_keypair, start_hash) = test_setup();
        // build two transactions with diff accounts
        let (_tx1, keys1, cost1) = build_simple_transaction(&mint_keypair, &start_hash);
        let second_account = Keypair::new();
        let (_tx2, keys2, cost2) = build_simple_transaction(&second_account, &start_hash);

        // build testee to have capacity for each chain, but not enough room for both transactions
        let mut testee = CostTracker::new(cmp::max(cost1, cost2), cost1 + cost2 - 1);
        // should have room for first transaction
        {
            assert!(testee
                .would_fit(&keys1, &cost1, &mut CostTrackerStats::default())
                .is_ok());
            testee.add_transaction(&keys1, &cost1);
        }
        // but no more room for package as whole
        {
            assert!(testee
                .would_fit(&keys2, &cost2, &mut CostTrackerStats::default())
                .is_err());
        }
    }

    #[test]
    fn test_cost_tracker_try_add_is_atomic() {
        let (mint_keypair, start_hash) = test_setup();
        let (tx, _keys, _cost) = build_simple_transaction(&mint_keypair, &start_hash);
        let tx = SanitizedTransaction::try_from(tx).unwrap();

        let acct1 = Pubkey::new_unique();
        let acct2 = Pubkey::new_unique();
        let acct3 = Pubkey::new_unique();
        let cost = 100;
        let account_max = cost * 2;
        let block_max = account_max * 3; // for three accts

        let mut testee = CostTracker::new(account_max, block_max);

        // case 1: a tx writes to 3 accounts, should success, we will have:
        // | acct1 | $cost |
        // | acct2 | $cost |
        // | acct2 | $cost |
        // and block_cost = $cost
        {
            let tx_cost = TransactionCost {
                writable_accounts: vec![acct1, acct2, acct3],
                execution_cost: cost,
                ..TransactionCost::default()
            };
            assert!(testee
                .try_add(&tx, &tx_cost, &mut CostTrackerStats::default())
                .is_ok());
            let stat = testee.get_stats();
            assert_eq!(cost, stat.total_cost);
            assert_eq!(3, stat.number_of_accounts);
            assert_eq!(cost, stat.costliest_account_cost);
        }

        // case 2: add tx writes to acct2 with $cost, should succeed, result to
        // | acct1 | $cost |
        // | acct2 | $cost * 2 |
        // | acct2 | $cost |
        // and block_cost = $cost * 2
        {
            let tx_cost = TransactionCost {
                writable_accounts: vec![acct2],
                execution_cost: cost,
                ..TransactionCost::default()
            };
            assert!(testee
                .try_add(&tx, &tx_cost, &mut CostTrackerStats::default())
                .is_ok());
            let stat = testee.get_stats();
            assert_eq!(cost * 2, stat.total_cost);
            assert_eq!(3, stat.number_of_accounts);
            assert_eq!(cost * 2, stat.costliest_account_cost);
            assert_eq!(acct2, stat.costliest_account);
        }

        // case 3: add tx writes to [acct1, acct2], acct2 exceeds limit, should failed atomically,
        // we shoudl still have:
        // | acct1 | $cost |
        // | acct2 | $cost |
        // | acct2 | $cost |
        // and block_cost = $cost
        {
            let tx_cost = TransactionCost {
                writable_accounts: vec![acct1, acct2],
                execution_cost: cost,
                ..TransactionCost::default()
            };
            assert!(testee
                .try_add(&tx, &tx_cost, &mut CostTrackerStats::default())
                .is_err());
            let stat = testee.get_stats();
            assert_eq!(cost * 2, stat.total_cost);
            assert_eq!(3, stat.number_of_accounts);
            assert_eq!(cost * 2, stat.costliest_account_cost);
            assert_eq!(acct2, stat.costliest_account);
        }
    }
}