Optimize when to acquire ledgers from the network.

Particularly avoid acquiring ledgers likely to be
produced locally very soon.

Derived from XRPLF#4764

Co-authored-by: Mark Travis <mtravis@ripple.com>

Author: ximinez

src/xrpld/app/ledger/InboundLedger.h

@@ -57,8 +57,10 @@ class InboundLedger final : public TimeoutCounter,
     ~InboundLedger();
 
     // Called when another attempt is made to fetch this same ledger
-    void
-    update(std::uint32_t seq);
+    //
+    // Returns true if this triggers requests to be sent
+    bool
+    update(std::uint32_t seq, bool broadcast);
 
     /** Returns true if we got all the data. */
     bool
@@ -89,7 +91,7 @@ class InboundLedger final : public TimeoutCounter,
     bool
     checkLocal();
     void
-    init(ScopedLockType& collectionLock);
+    init(ScopedLockType& collectionLock, bool broadcast);
 
     bool
     gotData(

src/xrpld/app/ledger/detail/InboundLedger.cpp

@@ -102,7 +102,7 @@ InboundLedger::InboundLedger(
 }
 
 void
-InboundLedger::init(ScopedLockType& collectionLock)
+InboundLedger::init(ScopedLockType& collectionLock, bool broadcast)
 {
     ScopedLockType sl(mtx_);
     collectionLock.unlock();
@@ -113,8 +113,18 @@ InboundLedger::init(ScopedLockType& collectionLock)
 
     if (!complete_)
     {
-        addPeers();
-        queueJob(sl);
+        if (broadcast)
+        {
+            addPeers();
+            queueJob(sl);
+        }
+        else
+        {
+            // Delay to give time to build the ledger before sending
+            JLOG(journal_.debug()) << "init: Deferring peer requests";
+            deferred_ = true;
+            setTimer(sl);
+        }
         return;
     }
 
@@ -144,8 +154,8 @@ InboundLedger::getPeerCount() const
     });
 }
 
-void
-InboundLedger::update(std::uint32_t seq)
+bool
+InboundLedger::update(std::uint32_t seq, bool broadcast)
 {
     ScopedLockType sl(mtx_);
 
@@ -155,6 +165,27 @@ InboundLedger::update(std::uint32_t seq)
 
     // Prevent this from being swept
     touch();
+
+    // If the signal is to broadcast, and this request has never tried to
+    // broadcast before, cancel any waiting timer, then fire off the job to
+    // broadcast. Note that this is calling mPeerSet->getPeerIds(), not
+    // getPeerCount(), because the latter will filter out peers that have been
+    // tried, but are since lost. This wants to check if peers have _ever_ been
+    // tried. If they have, stick with the normal timer flow.
+    if (broadcast && mPeerSet->getPeerIds().empty())
+    {
+        if (cancelTimer(sl))
+        {
+            JLOG(journal_.debug())
+                << "update: cancelling timer to send peer requests";
+            deferred_ = false;
+            skipNext_ = true;
+            addPeers();
+            queueJob(sl);
+            return true;
+        }
+    }
+    return false;
 }
 
 bool

src/xrpld/app/ledger/detail/InboundLedgers.cpp

@@ -110,20 +110,29 @@ class InboundLedgersImp : public InboundLedgers
                 // the network, and doesn't have the necessary tx's and
                 // ledger entries to build the ledger.
                 bool const isFull = app_.getOPs().isFull();
+                // fallingBehind means the last closed ledger is at least 2
+                // behind the validated ledger. If the node is falling
+                // behind the network, it probably needs information from
+                // the network to catch up.
+                //
+                // The reason this should not simply be only at least 1
+                // behind the validated ledger is that a slight lag is
+                // normal case because some nodes get there slightly later
+                // than others. A difference of 2 means that at least a full
+                // ledger interval has passed, so the node is beginning to
+                // fall behind.
+                bool const fallingBehind = app_.getOPs().isFallingBehind();
                 // If everything else is ok, don't try to acquire the ledger
                 // if the requested seq is in the near future relative to
-                // the validated ledger. If the requested ledger is between
-                // 1 and 19 inclusive ledgers ahead of the valid ledger this
-                // node has not built it yet, but it's possible/likely it
-                // has the tx's necessary to build it and get caught up.
-                // Plus it might not become validated. On the other hand, if
-                // it's more than 20 in the future, this node should request
-                // it so that it can jump ahead and get caught up.
+                // the validated ledger. Because validations lag behind
+                // consensus, if we get any further behind than this, we
+                // risk losing sync, because we don't have the preferred
+                // ledger available.
                 LedgerIndex const validSeq =
                     app_.getLedgerMaster().getValidLedgerIndex();
-                constexpr std::size_t lagLeeway = 20;
-                bool const nearFuture =
-                    (seq > validSeq) && (seq < validSeq + lagLeeway);
+                constexpr std::size_t lagLeeway = 2;
+                bool const nearFuture = (validSeq > 0) && (seq > validSeq) &&
+                    (seq < validSeq + lagLeeway);
                 // If everything else is ok, don't try to acquire the ledger
                 // if the request is related to consensus. (Note that
                 // consensus calls usually pass a seq of 0, so nearFuture
@@ -132,6 +141,7 @@ class InboundLedgersImp : public InboundLedgers
                     reason == InboundLedger::Reason::CONSENSUS;
                 ss << " Evaluating whether to broadcast requests to peers"
                    << ". full: " << (isFull ? "true" : "false")
+                   << ". falling behind: " << (fallingBehind ? "true" : "false")
                    << ". ledger sequence " << seq
                    << ". Valid sequence: " << validSeq
                    << ". Lag leeway: " << lagLeeway
@@ -142,6 +152,9 @@ class InboundLedgersImp : public InboundLedgers
                 // If the node is not synced, send requests.
                 if (!isFull)
                     return true;
+                // If the node is falling behind, send requests.
+                if (fallingBehind)
+                    return true;
                 // If the ledger is in the near future, do NOT send requests.
                 // This node is probably about to build it.
                 if (nearFuture)
@@ -152,7 +165,7 @@ class InboundLedgersImp : public InboundLedgers
                     return false;
                 return true;
             }();
-            ss << ". Would broadcast to peers? "
+            ss << ". Broadcast to peers? "
                << (shouldBroadcast ? "true." : "false.");
 
             if (!shouldAcquire)
@@ -187,7 +200,7 @@ class InboundLedgersImp : public InboundLedgers
                         std::ref(m_clock),
                         mPeerSetBuilder->build());
                     mLedgers.emplace(hash, inbound);
-                    inbound->init(sl);
+                    inbound->init(sl, shouldBroadcast);
                     ++mCounter;
                 }
             }
@@ -199,8 +212,12 @@ class InboundLedgersImp : public InboundLedgers
                 return {};
             }
 
-            if (!isNew)
-                inbound->update(seq);
+            bool const didBroadcast = [&]() {
+                if (!isNew)
+                    return inbound->update(seq, shouldBroadcast);
+                return shouldBroadcast;
+            }();
+            ss << " First broadcast: " << (didBroadcast ? "true" : "false");
 
             if (!inbound->isComplete())
             {

src/xrpld/app/ledger/detail/TimeoutCounter.cpp

@@ -55,23 +55,31 @@ TimeoutCounter::setTimer(ScopedLockType& sl)
     JLOG(journal_.debug()) << "Setting timer for " << timerInterval_.count()
                            << "ms";
     timer_.expires_after(timerInterval_);
-    timer_.async_wait(
-        [wptr = pmDowncast()](boost::system::error_code const& ec) {
-            if (ec == boost::asio::error::operation_aborted)
-                return;
-
-            if (auto ptr = wptr.lock())
+    timer_.async_wait([wptr =
+                           pmDowncast()](boost::system::error_code const& ec) {
+        if (auto ptr = wptr.lock())
+        {
+            ScopedLockType sl(ptr->mtx_);
+            if (ec == boost::asio::error::operation_aborted || ptr->skipNext_)
             {
                 JLOG(ptr->journal_.debug())
-                    << "timer: ec: " << ec << " (operation_aborted: "
-                    << boost::asio::error::operation_aborted << " - "
-                    << (ec == boost::asio::error::operation_aborted ? "aborted"
-                                                                    : "other")
-                    << ")";
-                ScopedLockType sl(ptr->mtx_);
-                ptr->queueJob(sl);
+                    << "Aborting setTimer: " << ec
+                    << ", skip: " << (ptr->skipNext_ ? "true" : "false");
+                ptr->skipNext_ = false;
+                return;
             }
-        });
+
+            ptr->queueJob(sl);
+        }
+    });
+}
+
+std::size_t
+TimeoutCounter::cancelTimer(ScopedLockType& sl)
+{
+    auto const ret = timer_.cancel();
+    JLOG(journal_.debug()) << "Cancelled " << ret << " timer(s)";
+    return ret;
 }
 
 void
@@ -108,9 +116,12 @@ TimeoutCounter::invokeOnTimer()
 
     if (!progress_)
     {
-        ++timeouts_;
-        JLOG(journal_.debug())
-            << "Timeout(" << timeouts_ << ") " << " acquiring " << hash_;
+        if (deferred_)
+            deferred_ = false;
+        else
+            ++timeouts_;
+        JLOG(journal_.debug()) << "Timeout(" << timeouts_ << ") "
+                               << " acquiring " << hash_;
         onTimer(false, sl);
     }
     else

src/xrpld/app/ledger/detail/TimeoutCounter.h

@@ -102,6 +102,10 @@ class TimeoutCounter
     void
     setTimer(ScopedLockType&);
 
+    /** Cancel any waiting timer */
+    std::size_t
+    cancelTimer(ScopedLockType&);
+
     /** Queue a job to call invokeOnTimer(). */
     void
     queueJob(ScopedLockType&);
@@ -133,6 +137,11 @@ class TimeoutCounter
     int timeouts_;
     bool complete_;
     bool failed_;
+    /** Whether the initialization deferred doing any work until the first
+     * timeout. */
+    bool deferred_ = false;
+    /** Skip the next timeout, regardless of ec */
+    bool skipNext_ = false;
     /** Whether forward progress has been made. */
     bool progress_;
     /** The minimum time to wait between calls to execute(). */

src/xrpld/app/misc/NetworkOPs.cpp

@@ -431,6 +431,8 @@ class NetworkOPsImp final : public NetworkOPs
     clearLedgerFetch() override;
     Json::Value
     getLedgerFetchInfo() override;
+    bool
+    isFallingBehind() const override;
     std::uint32_t
     acceptLedger(
         std::optional<std::chrono::milliseconds> consensusDelay) override;
@@ -721,6 +723,7 @@ class NetworkOPsImp final : public NetworkOPs
     std::atomic<bool> amendmentBlocked_{false};
     std::atomic<bool> amendmentWarned_{false};
     std::atomic<bool> unlBlocked_{false};
+    std::atomic<bool> fallingBehind_{false};
 
     ClosureCounter<void, boost::system::error_code const&> waitHandlerCounter_;
     boost::asio::steady_timer heartbeatTimer_;
@@ -1811,13 +1814,25 @@ NetworkOPsImp::beginConsensus(uint256 const& networkClosed)
 
     auto closingInfo = m_ledgerMaster.getCurrentLedger()->info();
 
-    JLOG(m_journal.info()) << "Consensus time for #" << closingInfo.seq
+    JLOG(m_journal.info()) << "beginConsensus time for #" << closingInfo.seq
                            << " with LCL " << closingInfo.parentHash;
 
-    auto prevLedger = m_ledgerMaster.getLedgerByHash(closingInfo.parentHash);
+    fallingBehind_ = false;
+    if (closingInfo.seq < m_ledgerMaster.getValidLedgerIndex() - 1)
+    {
+        fallingBehind_ = true;
+        JLOG(m_journal.warn())
+            << "beginConsensus Current ledger " << closingInfo.seq
+            << " is at least 2 behind validated "
+            << m_ledgerMaster.getValidLedgerIndex();
+    }
+
+    auto const prevLedger =
+        m_ledgerMaster.getLedgerByHash(closingInfo.parentHash);
 
     if (!prevLedger)
     {
+        fallingBehind_ = true;
         // this shouldn't happen unless we jump ledgers
         if (mMode == OperatingMode::FULL)
         {
@@ -1865,7 +1880,7 @@ NetworkOPsImp::beginConsensus(uint256 const& networkClosed)
         mLastConsensusPhase = currPhase;
     }
 
-    JLOG(m_journal.debug()) << "Initiating consensus engine";
+    JLOG(m_journal.debug()) << "beginConsensus Initiating consensus engine";
     return true;
 }
 
@@ -1938,7 +1953,7 @@ NetworkOPsImp::endConsensus()
     {
         // check if the ledger is good enough to go to FULL
         // Note: Do not go to FULL if we don't have the previous ledger
-        // check if the ledger is bad enough to go to CONNECTE  D -- TODO
+        // check if the ledger is bad enough to go to CONNECTED -- TODO
         auto current = m_ledgerMaster.getCurrentLedger();
         if (app_.timeKeeper().now() < (current->info().parentCloseTime +
                                        2 * current->info().closeTimeResolution))
@@ -2751,6 +2766,12 @@ NetworkOPsImp::getLedgerFetchInfo()
     return app_.getInboundLedgers().getInfo();
 }
 
+bool
+NetworkOPsImp::isFallingBehind() const
+{
+    return fallingBehind_;
+}
+
 void
 NetworkOPsImp::pubProposedTransaction(
     std::shared_ptr<ReadView const> const& ledger,

src/xrpld/app/misc/NetworkOPs.h

@@ -227,6 +227,8 @@ class NetworkOPs : public InfoSub::Source
     clearLedgerFetch() = 0;
     virtual Json::Value
     getLedgerFetchInfo() = 0;
+    virtual bool
+    isFallingBehind() const = 0;
 
     /** Accepts the current transaction tree, return the new ledger's sequence