Count the number of explicitly duplicated nodes, and log it

- The "copied ledger" count may differ from the "Rotating:" count,
  because the latter will also count nodes from the cache.

include/xrpl/nodestore/DatabaseRotating.h

@@ -55,6 +55,9 @@ public:
     setRotationInFlight(LedgerIndex inFlight) = 0;
     virtual LedgerIndex
     getRotationInFlight() const = 0;
+
+    virtual std::uint64_t
+    getDuplicationCount() const = 0;
 };
 
 }  // namespace xrpl::NodeStore

include/xrpl/nodestore/detail/DatabaseRotatingImp.h

@@ -76,6 +76,9 @@ public:
     LedgerIndex
     getRotationInFlight() const override;
 
+    std::uint64_t
+    getDuplicationCount() const override;
+
 private:
     std::shared_ptr<Backend> writableBackend_;
     std::shared_ptr<Backend> archiveBackend_;
@@ -93,6 +96,9 @@ private:
     std::atomic<LedgerIndex> rotationInFlight_{0};
     std::atomic<std::uint64_t> copyForwardCount_{0};
     std::atomic<std::uint64_t> copyRejectCount_{0};
+    // Duplication count tracks the number of nodes that are directly duplicated because they're in
+    // the target ledger or cache.
+    std::atomic<std::uint64_t> duplicationCount_{0};
 
     std::shared_ptr<NodeObject>
     fetchNodeObject(uint256 const& hash, std::uint32_t, FetchReport& fetchReport, bool duplicate)

src/libxrpl/nodestore/DatabaseRotatingImp.cpp

@@ -56,6 +56,7 @@ DatabaseRotatingImp::rotate(
     std::shared_ptr<NodeStore::Backend> oldArchiveBackend;
     std::uint64_t copyForwards = 0;
     std::uint64_t copyRejects = 0;
+    std::uint64_t duplications = 0;
     {
         std::scoped_lock const lock(mutex_);
 
@@ -69,6 +70,7 @@ DatabaseRotatingImp::rotate(
 
         copyForwards = copyForwardCount_.exchange(0, std::memory_order_relaxed);
         copyRejects = copyRejectCount_.exchange(0, std::memory_order_relaxed);
+        duplications = duplicationCount_.exchange(0, std::memory_order_relaxed);
     }
 
     if (copyForwards > 0 || copyRejects > 0)
@@ -78,6 +80,11 @@ DatabaseRotatingImp::rotate(
                            "during the rotation window. Rejected "
                         << copyRejects;
     }
+    if (duplications > 0)
+    {
+        JLOG(j_.warn()) << "Rotating: duplicated " << duplications
+                        << " nodes into the writable backend for the current validated ledger.";
+    }
 
     f(newWritableBackendName, newArchiveBackendName);
 }
@@ -95,6 +102,12 @@ DatabaseRotatingImp::getRotationInFlight() const
     return rotationInFlight_.load(std::memory_order_acquire);
 }
 
+std::uint64_t
+DatabaseRotatingImp::getDuplicationCount() const
+{
+    return duplicationCount_.load(std::memory_order_acquire);
+}
+
 std::string
 DatabaseRotatingImp::getName() const
 {
@@ -214,7 +227,11 @@ DatabaseRotatingImp::fetchNodeObject(
                     writable = writableBackend_;
                 }
 
-                if (!duplicate)
+                if (duplicate)
+                {
+                    duplicationCount_.fetch_add(1, std::memory_order_relaxed);
+                }
+                else
                 {
                     JLOG(j_.debug()) << "Rotating: copy node for ledger " << ledgerSeq
                                      << " from archive to writable backend: " << hash;

src/xrpld/app/misc/SHAMapStoreImp.cpp

@@ -451,7 +451,8 @@ SHAMapStoreImp::run()
                 return;
             // Only log if we completed without a "health" abort
             JLOG(journal_.debug())
-                << "copied ledger " << validatedSeq << " nodecount " << nodeCount;
+                << "copied ledger " << validatedSeq << " duplicated "
+                << dbRotating_->getDuplicationCount() << " / " << nodeCount << " nodes";
 
             JLOG(journal_.debug()) << "freshening caches";
             freshenCaches();