From a3a72816af7c5985398390cc5397a507a8235de2 Mon Sep 17 00:00:00 2001
From: Gav Wood <i@gavwood.com>
Date: Tue, 7 Apr 2015 00:37:10 +0200
Subject: [PATCH] Don't send all transactions all the time - rather select a
 set of peers each time.

---
 libethereum/EthereumHost.cpp | 55 ++++++++++++++++++++++++------------
 libethereum/EthereumHost.h   |  2 ++
 2 files changed, 39 insertions(+), 18 deletions(-)

diff --git a/libethereum/EthereumHost.cpp b/libethereum/EthereumHost.cpp
index de85d94bb..cb29980fd 100644
--- a/libethereum/EthereumHost.cpp
+++ b/libethereum/EthereumHost.cpp
@@ -175,18 +175,25 @@ void EthereumHost::doWork()
 void EthereumHost::maintainTransactions()
 {
 	// Send any new transactions.
+	map<std::shared_ptr<EthereumPeer>, h256s> peerTransactions;
+	auto ts = m_tq.transactions();
+	for (auto const& i: ts)
+	{
+		bool unsent = !m_transactionsSent.count(i.first);
+		for (auto const& p: randomSelection(25, [&](EthereumPeer* p) { return p->m_requireTransactions || (unsent && !p->m_knownTransactions.count(i.first)); }))
+			peerTransactions[p].push_back(i.first);
+	}
 	for (auto p: peerSessions())
-		if (auto ep = p.first->cap<EthereumPeer>().get())
+		if (auto ep = p.first->cap<EthereumPeer>())
 		{
 			bytes b;
 			unsigned n = 0;
-			for (auto const& i: m_tq.transactions())
-				if (ep->m_requireTransactions || (!m_transactionsSent.count(i.first) && !ep->m_knownTransactions.count(i.first)))
-				{
-					b += i.second.rlp();
-					++n;
-					m_transactionsSent.insert(i.first);
-				}
+			for (auto const& h: peerTransactions[ep])
+			{
+				b += ts[h].rlp();
+				++n;
+				m_transactionsSent.insert(h);
+			}
 			ep->clearKnownTransactions();
 
 			if (n || ep->m_requireTransactions)
@@ -199,6 +206,27 @@ void EthereumHost::maintainTransactions()
 		}
 }
 
+std::vector<std::shared_ptr<EthereumPeer>> EthereumHost::randomSelection(unsigned _percent, std::function<bool(EthereumPeer*)> const& _allow)
+{
+	std::vector<std::shared_ptr<EthereumPeer>> candidates;
+	candidates.reserve(peerSessions().size());
+	for (auto const& j: peerSessions())
+	{
+		auto pp = j.first->cap<EthereumPeer>();
+		if (_allow(pp.get()))
+			candidates.push_back(pp);
+	}
+
+	std::vector<std::shared_ptr<EthereumPeer>> ret;
+	for (unsigned i = (peerSessions().size() * _percent + 99) / 100; i-- && candidates.size();)
+	{
+		unsigned n = rand() % candidates.size();
+		ret.push_back(std::move(candidates[n]));
+		candidates.erase(candidates.begin() + n);
+	}
+	return ret;
+}
+
 void EthereumHost::maintainBlocks(h256 _currentHash)
 {
 	// Send any new blocks.
@@ -206,17 +234,8 @@ void EthereumHost::maintainBlocks(h256 _currentHash)
 	{
 		clog(NetMessageSummary) << "Sending a new block (current is" << _currentHash << ", was" << m_latestBlockSent << ")";
 
-		std::vector<std::shared_ptr<EthereumPeer>> dispersal;
-		for (auto const& j: peerSessions())
-			if (!j.first->cap<EthereumPeer>()->m_knownBlocks.count(_currentHash))
-				dispersal.push_back(j.first->cap<EthereumPeer>());
-
-		for (unsigned i = (dispersal.size() + 3) / 4; i--;)
+		for (auto const& p: randomSelection(25, [&](EthereumPeer* p){return !p->m_knownBlocks.count(_currentHash); }))
 		{
-			unsigned n = rand() % dispersal.size();
-			auto p = std::move(dispersal[n]);
-			dispersal.erase(dispersal.begin() + n);
-
 			RLPStream ts;
 			p->prep(ts, NewBlockPacket, 2).appendRaw(m_chain.block(), 1).append(m_chain.details().totalDifficulty);
 
diff --git a/libethereum/EthereumHost.h b/libethereum/EthereumHost.h
index 06575092c..fad0b8edd 100644
--- a/libethereum/EthereumHost.h
+++ b/libethereum/EthereumHost.h
@@ -77,6 +77,8 @@ public:
 	bool isBanned(p2p::NodeId _id) const { return !!m_banned.count(_id); }
 
 private:
+	std::vector<std::shared_ptr<EthereumPeer>> randomSelection(unsigned _percent = 25, std::function<bool(EthereumPeer*)> const& _allow = [](EthereumPeer const*){ return true; });
+
 	/// Session is tell us that we may need (re-)syncing with the peer.
 	void noteNeedsSyncing(EthereumPeer* _who);