Hotfix: don't clone and cache not existing accounts

[GabrielePicco]

Greptile Overview

Updated On: 2025-10-02 10:45:46 UTC

Summary

This hotfix addresses a memory optimization issue in the account cloning system by preventing the cloning and caching of non-existent accounts. The changes introduce a new `DoesNotExist` variant to the `AccountClonerUnclonableReason` enum and implement logic to detect when accounts don't exist on-chain (empty system accounts with 0 lamports owned by the system program).

The implementation adds an early exit in the cloning logic that checks if an account is essentially empty (0 lamports + system program ownership) and marks it as unclonable rather than processing it. Additionally, the caching mechanism is updated to exclude these non-existent accounts from being stored in the cache, which should reduce memory usage and prevent unnecessary storage of default/empty account states.

This change fits well within the existing account cloning architecture, leveraging the established AccountClonerUnclonableReason enum pattern to categorize why certain accounts cannot be cloned. The modification maintains the existing API contract while adding more intelligent handling of edge cases that can occur when the RPC returns default system account data for accounts that don't actually exist on-chain.

Important Files Changed

Changed Files

Filename	Score	Overview
magicblock-account-cloner/src/account_cloner.rs	5/5	Added new DoesNotExist enum variant to categorize non-existent accounts
magicblock-account-cloner/src/remote_account_cloner_worker.rs	4/5	Implemented logic to detect and skip cloning of non-existent accounts, plus caching exclusion

Confidence score: 4/5

• This PR is safe to merge with minimal risk as it adds defensive logic without breaking existing functionality
• Score reflects well-structured changes that follow existing patterns, though the u64::MAX slot value could be more explicit
• Pay close attention to the remote worker implementation to ensure the non-existence detection logic is robust

Sequence Diagram

sequenceDiagram
    participant User
    participant RemoteAccountClonerWorker
    participant AccountFetcher
    participant AccountUpdates
    participant AccountDumper
    participant InternalAccountProvider
    participant Cache

    User->>RemoteAccountClonerWorker: "clone_account(pubkey)"
    RemoteAccountClonerWorker->>RemoteAccountClonerWorker: "can_clone() check permissions"
    
    alt cloning not allowed
        RemoteAccountClonerWorker->>User: "Unclonable: NoCloningAllowed"
    else cloning allowed
        RemoteAccountClonerWorker->>AccountUpdates: "get_last_known_update_slot(pubkey)"
        AccountUpdates->>RemoteAccountClonerWorker: "last_update_slot"
        
        RemoteAccountClonerWorker->>Cache: "get_last_clone_output_from_pubkey(pubkey)"
        Cache->>RemoteAccountClonerWorker: "cached_output (optional)"
        
        alt cache hit and recent
            RemoteAccountClonerWorker->>User: "return cached output"
        else cache miss or stale
            RemoteAccountClonerWorker->>InternalAccountProvider: "get_account(pubkey)"
            InternalAccountProvider->>RemoteAccountClonerWorker: "local_account (optional)"
            
            RemoteAccountClonerWorker->>RemoteAccountClonerWorker: "do_clone(pubkey, stage)"
            RemoteAccountClonerWorker->>RemoteAccountClonerWorker: "check blacklist"
            
            alt account blacklisted
                RemoteAccountClonerWorker->>User: "Unclonable: IsBlacklisted"
            else account not blacklisted
                RemoteAccountClonerWorker->>AccountFetcher: "fetch_account_chain_snapshot(pubkey)"
                AccountFetcher->>RemoteAccountClonerWorker: "account_chain_snapshot"
                
                alt account does not exist (empty system account)
                    RemoteAccountClonerWorker->>RemoteAccountClonerWorker: "check if lamports=0 and owner=system_program"
                    RemoteAccountClonerWorker->>User: "Unclonable: DoesNotExist"
                else account exists
                    alt account is FeePayer
                        RemoteAccountClonerWorker->>AccountDumper: "dump_feepayer_account(pubkey, lamports, owner)"
                        AccountDumper->>RemoteAccountClonerWorker: "signature"
                    else account is Undelegated
                        RemoteAccountClonerWorker->>AccountDumper: "dump_undelegated_account(pubkey, account)"
                        AccountDumper->>RemoteAccountClonerWorker: "signature"
                    else account is Delegated
                        RemoteAccountClonerWorker->>AccountDumper: "dump_delegated_account(pubkey, account, owner)"
                        AccountDumper->>RemoteAccountClonerWorker: "signature"
                    end
                    
                    RemoteAccountClonerWorker->>RemoteAccountClonerWorker: "do_clone_and_update_cache()"
                    
                    alt should_cache (not DoesNotExist)
                        RemoteAccountClonerWorker->>Cache: "insert(pubkey, clone_output)"
                    end
                    
                    RemoteAccountClonerWorker->>User: "Cloned: {account_chain_snapshot, signature}"
                end
            end
        end
    end

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[greptile-apps]

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[thlorenz]

LGTM even though I'm not sure how we'd ever encounter the case that this is fixing as I explained in my comment.

[thlorenz]

Did you verify that the RPC returns this? I thought it returns some user error if the account is not found or None see here.

[GabrielePicco]

In conjunto, None is mapped to an undelegated not existing account: https://github.com/magicblock-labs/conjunto/blob/0a1af762bad2657dbb642f6e6f6d0adc41f5cf8f/lockbox/src/account_chain_snapshot_provider.rs#L85