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consensus: correctly save reference to previous height precommits (backport #9760) (#9775)

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* consensus: correctly save reference to previous height precommits (#9760)

This change reduces the number of Precommit messages sent to peers by 50%.

During the `ApplyNewRoundStepMessage`, we update the known state of the peer sending us the message.

We set the value of `ps.PRS.Precommits` to nil in this method if the peer is entering a new height or round.
34ca3fb474/consensus/reactor.go (L1368)

We then assign `ps.PRS.LastCommit = ps.PRS.Precommits` if the peer is entering a new height only - this does not happen during just a round change. This therefore results in `ps.PRS.LastCommit` having the value `nil`.

When the `LastCommit` bit field is seen as `nil` in the reactor, an empty bit field is initialized.
34ca3fb474/consensus/reactor.go (L1273)

The code responsible for gossiping votes from the previous height uses this `LastCommit` value and, seeing an empty `LastCommit` will resend every `Precommit` from the previous height since it lost the information it previously had detailing which precommits from the previous height the peer had.

This can be seen in the code responsible for gossiping precommits from the previous height:
34ca3fb474/consensus/reactor.go (L773)

Where this code grabs the, previously `nil`, `LastCommit` bit field:
34ca3fb474/consensus/reactor.go (L1204-L1212)

---

#### PR checklist

- [ ] Tests written/updated, or no tests needed
- [ ] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [ ] Updated relevant documentation (`docs/`) and code comments, or no
      documentation updates needed

(cherry picked from commit da204d371d)

# Conflicts:
#	CHANGELOG_PENDING.md

* changelog

Co-authored-by: William Banfield <4561443+williambanfield@users.noreply.github.com>
Co-authored-by: William Banfield <wbanfield@gmail.com>
This commit is contained in:
mergify[bot]
2022-11-28 15:26:09 -05:00
committed by GitHub
parent 92c797e353
commit 5703cc3455
2 changed files with 3 additions and 1 deletions
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1
CHANGELOG_PENDING.md
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@@ -45,6 +45,7 @@ Friendly reminder, we have a [bug bounty program](https://hackerone.com/tendermi
- [proto] \#9356 Migrate from `gogo/protobuf` to `cosmos/gogoproto` (@julienrbrt)
- [rpc] \#9276 Added `header` and `header_by_hash` queries to the RPC client (@samricotta)
- [abci] \#5706 Added `AbciVersion` to `RequestInfo` allowing applications to check ABCI version when connecting to Tendermint. (@marbar3778)
- [consensus] \#9760 Save peer LastCommit correctly to achieve 50% reduction in gossiped precommits. (@williambanfield)
### BUG FIXES

3
consensus/reactor.go
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@@ -1294,6 +1294,7 @@ func (ps *PeerState) ApplyNewRoundStepMessage(msg *NewRoundStepMessage) {
psRound := ps.PRS.Round
psCatchupCommitRound := ps.PRS.CatchupCommitRound
psCatchupCommit := ps.PRS.CatchupCommit
lastPrecommits := ps.PRS.Precommits
startTime := tmtime.Now().Add(-1 * time.Duration(msg.SecondsSinceStartTime) * time.Second)
ps.PRS.Height = msg.Height
@@ -1321,7 +1322,7 @@ func (ps *PeerState) ApplyNewRoundStepMessage(msg *NewRoundStepMessage) {
// Shift Precommits to LastCommit.
if psHeight+1 == msg.Height && psRound == msg.LastCommitRound {
ps.PRS.LastCommitRound = msg.LastCommitRound
ps.PRS.LastCommit = ps.PRS.Precommits
ps.PRS.LastCommit = lastPrecommits
} else {
ps.PRS.LastCommitRound = msg.LastCommitRound
ps.PRS.LastCommit = nil