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feat: syncer: optimize syncFork for one-epoch forks #11533

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Dec 18, 2023
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feat: syncer: optimize syncFork for one-epoch forks #11533

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29 changes: 29 additions & 0 deletions chain/sync.go
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Original file line number Diff line number Diff line change
Expand Up @@ -886,6 +886,35 @@ func (syncer *Syncer) syncFork(ctx context.Context, incoming *types.TipSet, know
}
}

incomingParentsTsk := incoming.Parents()
commonParent := false
for _, incomingParent := range incomingParentsTsk.Cids() {
if known.Contains(incomingParent) {
commonParent = true
}
}

if commonParent {
// known contains at least one of incoming's Parents => the common ancestor is known's Parents (incoming's Grandparents)
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Pretty sure this is a typo, as I parse it we only have the guarantee about common grandparents

2023-12-15-223158_1222x936_scrot

Suggested change
// known contains at least one of incoming's Parents => the common ancestor is known's Parents (incoming's Grandparents)
// known contains at least one of incoming's Parents => the common ancestor is known's Grandparents (also incoming's Grandparents)

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(the logic does appear to be correct tho)

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@magik6k No, I don't think this is right? The logic in 891-895 is checking whether incoming.Parents() has any blocks in common with known (so known = {A,B,C,D} in your diagram).

// in this case, we need to return {incoming, incoming.Parents()}
incomingParents, err := syncer.store.LoadTipSet(ctx, incomingParentsTsk)
if err != nil {
// fallback onto the network
tips, err := syncer.Exchange.GetBlocks(ctx, incoming.Parents(), 1)
if err != nil {
return nil, xerrors.Errorf("failed to fetch incomingParents from the network: %w", err)
}

if len(tips) == 0 {
return nil, xerrors.Errorf("network didn't return any tipsets")
}

incomingParents = tips[0]
}

return []*types.TipSet{incoming, incomingParents}, nil
}

// TODO: Does this mean we always ask for ForkLengthThreshold blocks from the network, even if we just need, like, 2? Yes.
// Would it not be better to ask in smaller chunks, given that an ~ForkLengthThreshold is very rare?
tips, err := syncer.Exchange.GetBlocks(ctx, incoming.Parents(), int(build.ForkLengthThreshold))
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