added cache hit rate to server info (#220)

src/backend/SimpleCache.cpp

@@ -53,11 +53,13 @@ SimpleCache::getSuccessor(ripple::uint256 const& key, uint32_t seq) const
     if (!full_)
         return {};
     std::shared_lock{mtx_};
+    successorReqCounter_++;
     if (seq != latestSeq_)
         return {};
     auto e = map_.upper_bound(key);
     if (e == map_.end())
         return {};
+    successorHitCounter_++;
     return {{e->first, e->second.blob}};
 }
 
@@ -81,11 +83,13 @@ SimpleCache::get(ripple::uint256 const& key, uint32_t seq) const
     if (seq > latestSeq_)
         return {};
     std::shared_lock lck{mtx_};
+    objectReqCounter_++;
     auto e = map_.find(key);
     if (e == map_.end())
         return {};
     if (seq < e->second.seq)
         return {};
+    objectHitCounter_++;
     return {e->second.blob};
 }
 
@@ -117,4 +121,18 @@ SimpleCache::size() const
     std::shared_lock lck{mtx_};
     return map_.size();
 }
+float
+SimpleCache::getObjectHitRate() const
+{
+    if (!objectReqCounter_)
+        return 1;
+    return ((float)objectHitCounter_) / objectReqCounter_;
+}
+float
+SimpleCache::getSuccessorHitRate() const
+{
+    if (!successorReqCounter_)
+        return 1;
+    return ((float)successorHitCounter_) / successorReqCounter_;
+}
 }  // namespace Backend

src/backend/SimpleCache.h

@@ -18,6 +18,13 @@ class SimpleCache
         Blob blob;
     };
 
+    // counters for fetchLedgerObject(s) hit rate
+    mutable std::atomic_uint32_t objectReqCounter_;
+    mutable std::atomic_uint32_t objectHitCounter_;
+    // counters for fetchSuccessorKey hit rate
+    mutable std::atomic_uint32_t successorReqCounter_;
+    mutable std::atomic_uint32_t successorHitCounter_;
+
     std::map<ripple::uint256, CacheEntry> map_;
     mutable std::shared_mutex mtx_;
     uint32_t latestSeq_ = 0;
@@ -62,6 +69,12 @@ public:
 
     size_t
     size() const;
+
+    float
+    getObjectHitRate() const;
+
+    float
+    getSuccessorHitRate() const;
 };
 
 }  // namespace Backend

src/rpc/handlers/ServerInfo.cpp

@@ -90,6 +90,9 @@ doServerInfo(Context const& context)
     cache["is_full"] = context.backend->cache().isFull();
     cache["latest_ledger_seq"] =
         context.backend->cache().latestLedgerSequence();
+    cache["object_hit_rate"] = context.backend->cache().getObjectHitRate();
+    cache["successor_hit_rate"] =
+        context.backend->cache().getSuccessorHitRate();
 
     if (admin)
     {