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## Issue Addressed Closes #800 Closes #1713 ## Proposed Changes Implement the temporary state storage algorithm described in #800. Specifically: * Add `DBColumn::BeaconStateTemporary`, for storing 0-length temporary marker values. * Store intermediate states immediately as they are created, marked temporary. Delete the temporary flag if the block is processed successfully. * Add a garbage collection process to delete leftover temporary states on start-up. * Bump the database schema version to 2 so that a DB with temporary states can't accidentally be used with older versions of the software. The auto-migration is a no-op, but puts in place some infra that we can use for future migrations (e.g. #1784) ## Additional Info There are two known race conditions, one potentially causing permanent faults (hopefully rare), and the other insignificant. ### Race 1: Permanent state marked temporary EDIT: this has been fixed by the addition of a lock around the relevant critical section There are 2 threads that are trying to store 2 different blocks that share some intermediate states (e.g. they both skip some slots from the current head). Consider this sequence of events: 1. Thread 1 checks if state `s` already exists, and seeing that it doesn't, prepares an atomic commit of `(s, s_temporary_flag)`. 2. Thread 2 does the same, but also gets as far as committing the state txn, finishing the processing of its block, and _deleting_ the temporary flag. 3. Thread 1 is (finally) scheduled again, and marks `s` as temporary with its transaction. 4. a) The process is killed, or thread 1's block fails verification and the temp flag is not deleted. This is a permanent failure! Any attempt to load state `s` will fail... hope it isn't on the main chain! Alternatively (4b) happens... b) Thread 1 finishes, and re-deletes the temporary flag. In this case the failure is transient, state `s` will disappear temporarily, but will come back once thread 1 finishes running. I _hope_ that steps 1-3 only happen very rarely, and 4a even more rarely. It's hard to know This once again begs the question of why we're using LevelDB (#483), when it clearly doesn't care about atomicity! A ham-fisted fix would be to wrap the hot and cold DBs in locks, which would bring us closer to how other DBs handle read-write transactions. E.g. [LMDB only allows one R/W transaction at a time](https://docs.rs/lmdb/0.8.0/lmdb/struct.Environment.html#method.begin_rw_txn). ### Race 2: Temporary state returned from `get_state` I don't think this race really matters, but in `load_hot_state`, if another thread stores a state between when we call `load_state_temporary_flag` and when we call `load_hot_state_summary`, then we could end up returning that state even though it's only a temporary state. I can't think of any case where this would be relevant, and I suspect if it did come up, it would be safe/recoverable (having data is safer than _not_ having data). This could be fixed by using a LevelDB read snapshot, but that would require substantial changes to how we read all our values, so I don't think it's worth it right now. |
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Lighthouse: Ethereum 2.0
An open-source Ethereum 2.0 client, written in Rust and maintained by Sigma Prime.
Overview
Lighthouse is:
- Fully open-source, licensed under Apache 2.0.
- Security-focused. Fuzzing has begun and security reviews are underway.
- Built in Rust, a modern language providing unique safety guarantees and excellent performance (comparable to C++).
- Funded by various organisations, including Sigma Prime, the Ethereum Foundation, ConsenSys and private individuals.
- Actively involved in the specification and security analysis of the emerging Ethereum 2.0 specification.
Like all Ethereum 2.0 clients, Lighthouse is a work-in-progress.
Development Status
Current development overview:
- Specification
v0.12.3implemented, optimized and passing test vectors. - Rust-native libp2p with Gossipsub and Discv5.
- RESTful JSON API via HTTP server.
- Events via WebSocket.
- Metrics via Prometheus.
Roadmap
April 2019: Inital single-client testnets.September 2019: Inter-operability with other Ethereum 2.0 clients.Q1 2020:lighthouse-0.1.0release: All major phase 0 features implemented.Q2 2020: Public, multi-client testnet with user-facing functionality.Q2 2020: Third-party security review.- Q3 2020: Additional third-party security reviews.
- Q3 2020: Long-lived, multi-client Beacon Chain testnet
- Q4 2020: Production Beacon Chain (tentative).
Documentation
The Lighthouse Book contains information for testnet users and developers.
If you'd like some background on Sigma Prime, please see the Lighthouse Update #00 blog post or sigmaprime.io.
Contributing
Lighthouse welcomes contributors.
If you are looking to contribute, please head to the Contributing section of the Lighthouse book.
Contact
The best place for discussion is the Lighthouse Discord server. Alternatively, you may use the sigp/lighthouse gitter.
Encrypt sensitive messages using our PGP key.
Donations
Lighthouse is an open-source project and a public good. Funding public goods is hard and we're grateful for the donations we receive from the community via:
- Gitcoin Grants.
- Ethereum address:
0x25c4a76E7d118705e7Ea2e9b7d8C59930d8aCD3b(donation.sigmaprime.eth).