Reduce number of async fetches

src/ripple_core/nodestore/impl/DatabaseImp.h

@@ -130,7 +130,9 @@ public:
     int getDesiredAsyncReadCount ()
     {
         // We prefer a client not fill our cache
-        return m_cache.getTargetSize() / 4;
+        // We don't want to push data out of the cache
+        // before it's retrieved
+        return m_cache.getTargetSize() / asyncDivider;
     }
 
     NodeObject::Ptr fetch (uint256 const& hash)

src/ripple_core/nodestore/impl/Tuning.h

@@ -30,6 +30,9 @@ enum
 
     // Expiration time for cached nodes
     ,cacheTargetSeconds = 300
+
+    // Fraction of the cache one query source can take
+    ,asyncDivider = 8
 };
 
 }