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downloader: different sync strategy

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This commit is contained in:
Martin Holst Swende
2018-11-12 14:18:56 +01:00
committed by Péter Szilágyi
parent 68be45e5f8
commit 51b2f1620c
2 changed files with 157 additions and 41 deletions
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122
eth/downloader/downloader.go
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@ -430,7 +430,7 @@ func (d *Downloader) syncWithPeer(p *peerConnection, hash common.Hash, td *big.I
}
height := latest.Number.Uint64()
origin, err := d.findAncestor(p, height)
origin, err := d.findAncestor(p, latest)
if err != nil {
return err
}
@ -587,41 +587,85 @@ func (d *Downloader) fetchHeight(p *peerConnection) (*types.Header, error) {
}
}
// calculateRequestSpan calculates what headers to request from a peer when trying to determine the
// common ancestor.
// It returns parameters to be used for peer.RequestHeadersByNumber:
// from - starting block number
// count - number of headers to request
// skip - number of headers to skip
// and also returns 'max', the last block which is expected to be returned by the remote peers,
// given the (from,count,skip)
func calculateRequestSpan(remoteHeight, localHeight uint64) (int64, int, int, uint64) {
var (
from int
count int
MaxCount = MaxHeaderFetch / 16
)
// requestHead is the highest block that we will ask for. If requestHead is not offset,
// the highest block that we will get is 16 blocks back from head, which means we
// will fetch 14 or 15 blocks unnecessarily in the case the height difference
// between us and the peer is 1-2 blocks, which is most common
requestHead := int(remoteHeight) - 1
if requestHead < 0 {
requestHead = 0
}
// requestBottom is the lowest block we want included in the query
// Ideally, we want to include just below own head
requestBottom := int(localHeight - 1)
if requestBottom < 0 {
requestBottom = 0
}
totalSpan := requestHead - requestBottom
span := 1 + totalSpan/MaxCount
if span < 2 {
span = 2
}
if span > 16 {
span = 16
}
count = 1 + totalSpan/span
if count > MaxCount {
count = MaxCount
}
if count < 2 {
count = 2
}
from = requestHead - (count-1)*span
if from < 0 {
from = 0
}
max := from + (count-1)*span
return int64(from), count, span - 1, uint64(max)
}
// findAncestor tries to locate the common ancestor link of the local chain and
// a remote peers blockchain. In the general case when our node was in sync and
// on the correct chain, checking the top N links should already get us a match.
// In the rare scenario when we ended up on a long reorganisation (i.e. none of
// the head links match), we do a binary search to find the common ancestor.
func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, error) {
func (d *Downloader) findAncestor(p *peerConnection, remoteHeader *types.Header) (uint64, error) {
// Figure out the valid ancestor range to prevent rewrite attacks
floor, ceil := int64(-1), d.lightchain.CurrentHeader().Number.Uint64()
var (
floor = int64(-1)
localHeight uint64
remoteHeight = remoteHeader.Number.Uint64()
)
switch d.mode {
case FullSync:
localHeight = d.blockchain.CurrentBlock().NumberU64()
case FastSync:
localHeight = d.blockchain.CurrentFastBlock().NumberU64()
default:
localHeight = d.lightchain.CurrentHeader().Number.Uint64()
}
p.log.Debug("Looking for common ancestor", "local", localHeight, "remote", remoteHeight)
if localHeight >= MaxForkAncestry {
floor = int64(localHeight - MaxForkAncestry)
}
if d.mode == FullSync {
ceil = d.blockchain.CurrentBlock().NumberU64()
} else if d.mode == FastSync {
ceil = d.blockchain.CurrentFastBlock().NumberU64()
}
if ceil >= MaxForkAncestry {
floor = int64(ceil - MaxForkAncestry)
}
p.log.Debug("Looking for common ancestor", "local", ceil, "remote", height)
// Request the topmost blocks to short circuit binary ancestor lookup
head := ceil
if head > height {
head = height
}
from := int64(head) - int64(MaxHeaderFetch)
if from < 0 {
from = 0
}
// Span out with 15 block gaps into the future to catch bad head reports
limit := 2 * MaxHeaderFetch / 16
count := 1 + int((int64(ceil)-from)/16)
if count > limit {
count = limit
}
go p.peer.RequestHeadersByNumber(uint64(from), count, 15, false)
from, count, skip, max := calculateRequestSpan(remoteHeight, localHeight)
go p.peer.RequestHeadersByNumber(uint64(from), count, skip, false)
// Wait for the remote response to the head fetch
number, hash := uint64(0), common.Hash{}
@ -647,9 +691,10 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
return 0, errEmptyHeaderSet
}
// Make sure the peer's reply conforms to the request
for i := 0; i < len(headers); i++ {
if number := headers[i].Number.Int64(); number != from+int64(i)*16 {
p.log.Warn("Head headers broke chain ordering", "index", i, "requested", from+int64(i)*16, "received", number)
for i, header := range headers {
expectNumber := from + int64(i)*int64((skip+1))
if number := header.Number.Int64(); number != expectNumber {
p.log.Warn("Head headers broke chain ordering", "index", i, "requested", expectNumber, "received", number)
return 0, errInvalidChain
}
}
@ -657,20 +702,15 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
finished = true
for i := len(headers) - 1; i >= 0; i-- {
// Skip any headers that underflow/overflow our requested set
if headers[i].Number.Int64() < from || headers[i].Number.Uint64() > ceil {
if headers[i].Number.Int64() < from || headers[i].Number.Uint64() > max {
continue
}
// Otherwise check if we already know the header or not
h := headers[i].Hash()
n := headers[i].Number.Uint64()
if (d.mode == FullSync && d.blockchain.HasBlock(h, n)) || (d.mode != FullSync && d.lightchain.HasHeader(h, n)) {
if (d.mode == FullSync && d.blockchain.HasBlock(h, n)) ||
(d.mode != FullSync && d.lightchain.HasHeader(h, n)) {
number, hash = n, h
// If every header is known, even future ones, the peer straight out lied about its head
if number > height && i == limit-1 {
p.log.Warn("Lied about chain head", "reported", height, "found", number)
return 0, errStallingPeer
}
break
}
}
@ -694,7 +734,7 @@ func (d *Downloader) findAncestor(p *peerConnection, height uint64) (uint64, err
return number, nil
}
// Ancestor not found, we need to binary search over our chain
start, end := uint64(0), head
start, end := uint64(0), remoteHeight
if floor > 0 {
start = uint64(floor)
}