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Reduce bandwidth during initial headers sync when a block is found

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If our headers chain is behind on startup, then if a block is found we'll try
to catch up from all peers announcing the block, in addition to our initial
headers-sync peer. This commit changes behavior so that in this situation,
we'll choose at most one peer announcing a block to additionally sync headers
from.
This commit is contained in:
Suhas Daftuar 2022-07-25 13:53:35 -04:00
parent 5671217477
commit 05f7f31598
1 changed files with 33 additions and 6 deletions
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31
src/net_processing.cpp
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@ -369,6 +369,9 @@ struct Peer {
/** Set of txids to reconsider once their parent transactions have been accepted **/
std::set<uint256> m_orphan_work_set GUARDED_BY(g_cs_orphans);
/** Whether we've sent this peer a getheaders in response to an inv prior to initial-headers-sync completing */
bool m_inv_triggered_getheaders_before_sync{false};
/** Protects m_getdata_requests **/
Mutex m_getdata_requests_mutex;
/** Work queue of items requested by this peer **/
@ -681,6 +684,9 @@ private:
/** Number of nodes with fSyncStarted. */
int nSyncStarted GUARDED_BY(cs_main) = 0;
/** Hash of the last block we received via INV */
uint256 m_last_block_inv_triggering_headers_sync{};
/**
* Sources of received blocks, saved to be able punish them when processing
* happens afterwards.
@ -3239,8 +3245,9 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
UpdateBlockAvailability(pfrom.GetId(), inv.hash);
if (!fAlreadyHave && !fImporting && !fReindex && !IsBlockRequested(inv.hash)) {
// Headers-first is the primary method of announcement on
// the network. If a node fell back to sending blocks by inv,
// it's probably for a re-org. The final block hash
// the network. If a node fell back to sending blocks by
// inv, it may be for a re-org, or because we haven't
// completed initial headers sync. The final block hash
// provided should be the highest, so send a getheaders and
// then fetch the blocks we need to catch up.
best_block = &inv.hash;
@ -3265,11 +3272,31 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
}
if (best_block != nullptr) {
// If we haven't started initial headers-sync with this peer, then
// consider sending a getheaders now. On initial startup, there's a
// reliability vs bandwidth tradeoff, where we are only trying to do
// initial headers sync with one peer at a time, with a long
// timeout (at which point, if the sync hasn't completed, we will
// disconnect the peer and then choose another). In the meantime,
// as new blocks are found, we are willing to add one new peer per
// block to sync with as well, to sync quicker in the case where
// our initial peer is unresponsive (but less bandwidth than we'd
// use if we turned on sync with all peers).
CNodeState& state{*Assert(State(pfrom.GetId()))};
if (state.fSyncStarted || (!peer->m_inv_triggered_getheaders_before_sync && *best_block != m_last_block_inv_triggering_headers_sync)) {
if (MaybeSendGetHeaders(pfrom, m_chainman.ActiveChain().GetLocator(m_chainman.m_best_header), *peer)) {
LogPrint(BCLog::NET, "getheaders (%d) %s to peer=%d\n",
m_chainman.m_best_header->nHeight, best_block->ToString(),
pfrom.GetId());
}
if (!state.fSyncStarted) {
peer->m_inv_triggered_getheaders_before_sync = true;
// Update the last block hash that triggered a new headers
// sync, so that we don't turn on headers sync with more
// than 1 new peer every new block.
m_last_block_inv_triggering_headers_sync = *best_block;
}
}
}
return;