Cache serialized mapblocks during sending

This reduces the
(absolute) time spent in Server::SendBlocks() from 700ms to 300ms
(relative) share of MapBlock::serialize() from 80% to 60%
in a test setup with 10 players and many block changes

diff --git a/src/server.cpp b/src/server.cpp
index 6a4349ba5dc2e7b7b2aca65cdf05ed54ab532264..d85a2e95ab5ce98d00f63dc4505547277bdc21e6 100644 (file)
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -2326,22 +2326,34 @@ void Server::sendMetadataChanged(const std::list<v3s16> &meta_updates, float far
 }
 
 void Server::SendBlockNoLock(session_t peer_id, MapBlock *block, u8 ver,
-               u16 net_proto_version)
+               u16 net_proto_version, SerializedBlockCache *cache)
 {
-       /*
-               Create a packet with the block in the right format
-       */
        thread_local const int net_compression_level = rangelim(g_settings->getS16("map_compression_level_net"), -1, 9);
-       std::ostringstream os(std::ios_base::binary);
-       block->serialize(os, ver, false, net_compression_level);
-       block->serializeNetworkSpecific(os);
-       std::string s = os.str();
+       std::string s, *sptr = nullptr;
 
-       NetworkPacket pkt(TOCLIENT_BLOCKDATA, 2 + 2 + 2 + s.size(), peer_id);
+       if (cache) {
+               auto it = cache->find({block->getPos(), ver});
+               if (it != cache->end())
+                       sptr = &it->second;
+       }
 
+       // Serialize the block in the right format
+       if (!sptr) {
+               std::ostringstream os(std::ios_base::binary);
+               block->serialize(os, ver, false, net_compression_level);
+               block->serializeNetworkSpecific(os);
+               s = os.str();
+               sptr = &s;
+       }
+
+       NetworkPacket pkt(TOCLIENT_BLOCKDATA, 2 + 2 + 2 + sptr->size(), peer_id);
        pkt << block->getPos();
-       pkt.putRawString(s.c_str(), s.size());
+       pkt.putRawString(*sptr);
        Send(&pkt);
+
+       // Store away in cache
+       if (cache && sptr == &s)
+               (*cache)[{block->getPos(), ver}] = std::move(s);
 }
 
 void Server::SendBlocks(float dtime)
@@ -2351,7 +2363,7 @@ void Server::SendBlocks(float dtime)
 
        std::vector<PrioritySortedBlockTransfer> queue;
 
-       u32 total_sending = 0;
+       u32 total_sending = 0, unique_clients = 0;
 
        {
                ScopeProfiler sp2(g_profiler, "Server::SendBlocks(): Collect list");
@@ -2366,7 +2378,9 @@ void Server::SendBlocks(float dtime)
                                continue;
 
                        total_sending += client->getSendingCount();
+                       const auto old_count = queue.size();
                        client->GetNextBlocks(m_env,m_emerge, dtime, queue);
+                       unique_clients += queue.size() > old_count ? 1 : 0;
                }
        }
 
@@ -2385,6 +2399,12 @@ void Server::SendBlocks(float dtime)
        ScopeProfiler sp(g_profiler, "Server::SendBlocks(): Send to clients");
        Map &map = m_env->getMap();
 
+       SerializedBlockCache cache, *cache_ptr = nullptr;
+       if (unique_clients > 1) {
+               // caching is pointless with a single client
+               cache_ptr = &cache;
+       }
+
        for (const PrioritySortedBlockTransfer &block_to_send : queue) {
                if (total_sending >= max_blocks_to_send)
                        break;
@@ -2399,7 +2419,7 @@ void Server::SendBlocks(float dtime)
                        continue;
 
                SendBlockNoLock(block_to_send.peer_id, block, client->serialization_version,
-                               client->net_proto_version);
+                               client->net_proto_version, cache_ptr);
 
                client->SentBlock(block_to_send.pos);
                total_sending++;

diff --git a/src/server.h b/src/server.h
index 5090a35792c25d6099d6091bcb7e051b116b819d..b1b9675d9ae05cae9e1a85df210b854685e40950 100644 (file)
--- a/src/server.h
+++ b/src/server.h
@@ -424,6 +424,16 @@ class Server : public con::PeerHandler, public MapEventReceiver,
                std::unordered_set<session_t> waiting_players;
        };
 
+       // the standard library does not implement std::hash for pairs so we have this:
+       struct SBCHash {
+               size_t operator() (const std::pair<v3s16, u16> &p) const {
+                       return (((size_t) p.first.X) << 48) | (((size_t) p.first.Y) << 32) |
+                               (((size_t) p.first.Z) << 16) | ((size_t) p.second);
+               }
+       };
+
+       typedef std::unordered_map<std::pair<v3s16, u16>, std::string, SBCHash> SerializedBlockCache;
+
        void init();
 
        void SendMovement(session_t peer_id);
@@ -484,7 +494,9 @@ class Server : public con::PeerHandler, public MapEventReceiver,
                        float far_d_nodes = 100);
 
        // Environment and Connection must be locked when called
-       void SendBlockNoLock(session_t peer_id, MapBlock *block, u8 ver, u16 net_proto_version);
+       // `cache` may only be very short lived! (invalidation not handeled)
+       void SendBlockNoLock(session_t peer_id, MapBlock *block, u8 ver,
+               u16 net_proto_version, SerializedBlockCache *cache = nullptr);
 
        // Sends blocks to clients (locks env and con on its own)
        void SendBlocks(float dtime);