To get started quickly with an example application, see the [quick start guide](introduction/quick-start.md).
To learn about application development on Tendermint, see the [Application Blockchain Interface](spec/abci/).
To learn about application development on Tendermint, see the [Application Blockchain Interface](https://github.com/tendermint/spec/tree/master/spec/abci).
For more details on using Tendermint, see the respective documentation for
[Tendermint Core](tendermint-core/), [benchmarking and monitoring](tools/), and [network deployments](networks/).
* 14-02-2020: Updated with the implementation details
- 18-06-2019: Initial draft
- 08-07-2019: Reviewed
- 29-11-2019: Implemented
- 14-02-2020: Updated with the implementation details
## Context
The blockchain reactor is responsible for two high level processes:sending/receiving blocks from peers and FastSync-ing blocks to catch upnode who is far behind. The goal of [ADR-40](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-040-blockchain-reactor-refactor.md) was to refactor these two processes by separating business logic currently wrapped up in go-channels into pure `handle*` functions. While the ADR specified what the final form of the reactor might look like it lacked guidance on intermediary steps to get there.
The following diagram illustrates the state of the [blockchain-reorg](https://github.com/tendermint/tendermint/pull/35610) reactor which will be referred to as `v1`.
The blockchain reactor is responsible for two high level processes:sending/receiving blocks from peers and FastSync-ing blocks to catch upnode who is far behind. The goal of [ADR-40](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-040-blockchain-reactor-refactor.md) was to refactor these two processes by separating business logic currently wrapped up in go-channels into pure `handle*` functions. While the ADR specified what the final form of the reactor might look like it lacked guidance on intermediary steps to get there.
The following diagram illustrates the state of the [blockchain-reorg](https://github.com/tendermint/tendermint/pull/3561) reactor which will be referred to as `v1`.
While `v1` of the blockchain reactor has shown significant improvements in terms of simplifying the concurrency model, the current PR has run into few roadblocks.
* The current PR large and difficult to review.
* Block gossiping and fast sync processes are highly coupled to the shared `Pool` data structure.
* Peer communication is spread over multiple components creating complex dependency graph which must be mocked out during testing.
* Timeouts modeled as stateful tickers introduce non-determinism in tests
- The current PR large and difficult to review.
- Block gossiping and fast sync processes are highly coupled to the shared `Pool` data structure.
- Peer communication is spread over multiple components creating complex dependency graph which must be mocked out during testing.
- Timeouts modeled as stateful tickers introduce non-determinism in tests
This ADR is meant to specify the missing components and control necessary to achieve [ADR-40](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-040-blockchain-reactor-refactor.md).
The reactor will include a demultiplexing routine which will send each message to each sub routine for independent processing. Each sub routine will then select the messages it's interested in and call the handle specific function specified in [ADR-40](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-040-blockchain-reactor-refactor.md). The demuxRoutine acts as "pacemaker" setting the time in which events are expected to be handled.
An io handling routine within the reactor will isolate peer communication. Message going through the ioRoutine will usually be one way, using `p2p` APIs. In the case in which the `p2p` API such as `trySend` return errors, the ioRoutine can funnel those message back to the demuxRoutine for distribution to the other routines. For instance errors from the ioRoutine can be consumed by the scheduler to inform better peer selection implementations.
The processor is responsible for ordering, verifying and executing blocks. The Processor will maintain an internal cursor `height` refering to the last processed block. As a set of blocks arrive unordered, the Processor will check if it has `height+1` necessary to process the next block. The processor also maintains the map `blockPeers` of peers to height, to keep track of which peer provided the block at `height`. `blockPeers` can be used in`handleRemovePeer(...)` to reschedule all unprocessed blocks provided by a peer who has errored.
The Schedule maintains the internal state used for scheduling blockRequestMessages based on some scheduling algorithm. The schedule needs to maintain state on:
* The state `blockState` of every block seem up to height of maxHeight
* The set of peers and their peer state `peerState`
* which peers have which blocks
* which blocks have been requested from which peers
- The state `blockState` of every block seem up to height of maxHeight
- The set of peers and their peer state `peerState`
- which peers have which blocks
- which blocks have been requested from which peers
```go
type blockState int
@ -256,7 +258,7 @@ type schedule {
// a map of peerID to schedule specific peer struct `scPeer`
peers map[p2p.ID]scPeer
// a map of heights to the peer we are waiting for a response from
pending map[height]scPeer
@ -309,6 +311,7 @@ type scPeer struct {
```
# Scheduler
The scheduler is configured to maintain a target `n` of in flight
messages and will use feedback from `_blockResponseMessage`,
`_statusResponseMessage` and `_peerError` produce an optimal assignment
@ -342,7 +345,7 @@ func handleTimeCheckEv(time) {
events = []
for peerID := range schedule.peersNotTouchedSince(time) {
pending = schedule.pendingFrom(peerID)
pending = schedule.pendingFrom(peerID)
schedule.setPeerState(peerID, timedout)
schedule.resetBlocks(pending)
events = append(events, peerTimeout{peerID})
@ -355,6 +358,7 @@ func handleTimeCheckEv(time) {
```
## Peer
The Peer Stores per peer state based on messages received by the scheduler.
```go
@ -376,19 +380,19 @@ type Peer struct {
This design is under active development. The Implementation has been
* Simulation becomes a-termporal: no need wait for a wall-time timeout
* Peer Selection can be independently tested/simulated
* Develop a general approach to refactoring reactors
- Test become deterministic
- Simulation becomes a-termporal: no need wait for a wall-time timeout
- Peer Selection can be independently tested/simulated
- Develop a general approach to refactoring reactors
### Negative
@ -396,11 +400,11 @@ staged in the following PRs:
### Implementation Path
* Implement the scheduler, test the scheduler, review the rescheduler
* Implement the processor, test the processor, review the processor
* Implement the demuxer, write integration test, review integration tests
- Implement the scheduler, test the scheduler, review the rescheduler
- Implement the processor, test the processor, review the processor
- Implement the demuxer, write integration test, review integration tests
## References
* [ADR-40](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-040-blockchain-reactor-refactor.md): The original blockchain reactor re-org proposal
* [Blockchain re-org](https://github.com/tendermint/tendermint/pull/3561): The current blockchain reactor re-org implementation (v1)
- [ADR-40](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-040-blockchain-reactor-refactor.md): The original blockchain reactor re-org proposal
- [Blockchain re-org](https://github.com/tendermint/tendermint/pull/3561): The current blockchain reactor re-org implementation (v1)
mergify[bot]
4 years ago
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