Periodically pause copying ledger nodes during online_delete

src/ripple/app/misc/SHAMapStoreImp.cpp

@@ -272,6 +272,12 @@ SHAMapStoreImp::copyNode(std::uint64_t& nodeCount, SHAMapTreeNode const& node)
         if (healthWait() == stopping)
             return false;
     }
+    if (!(nodeCount % backoffInterval_))
+    {
+        JLOG(journal_.trace())
+            << "copyNode backing off after " << nodeCount << " node writes";
+        std::this_thread::sleep_for(backOff_);
+    }
 
     return true;
 }

src/ripple/app/misc/SHAMapStoreImp.h

@@ -77,6 +77,9 @@ class SHAMapStoreImp : public SHAMapStore
     std::string const dbPrefix_ = "rippledb";
     // check health/stop status as records are copied
     std::uint64_t const checkHealthInterval_ = 1000;
+    // back off periodically to reduce write contention as records are copied
+    std::uint64_t const backoffInterval_ =
+        ripple::NodeStore::batchWriteLimitSize / 2;
     // minimum # of ledgers to maintain for health of network
     static std::uint32_t const minimumDeletionInterval_ = 256;
     // minimum # of ledgers required for standalone mode.