Prevent database fragmentation

Signed-off-by: Anthony Fieroni <[email protected]>

src/flushablestorage.h

@@ -134,6 +134,7 @@ class CStorageLevelDB : public CStorageKV {
         return true;
     }
     bool Erase(const TBytes& key) override {
+        begin.empty() ? (begin = key) : (end = key);
         batch.Erase(refTBytes(key));
         return true;
     }
@@ -144,6 +145,12 @@ class CStorageLevelDB : public CStorageKV {
     bool Flush() override { // Commit batch
         auto result = db.WriteBatch(batch);
         batch.Clear();
+        // prevent db fragmentation
+        if (!begin.empty() && !end.empty()) {
+            db.CompactRange(refTBytes(begin), refTBytes(end));
+        }
+        end.clear();
+        begin.clear();
         return result;
     }
     size_t SizeEstimate() const override {
@@ -157,6 +164,8 @@ class CStorageLevelDB : public CStorageKV {
     }
 
 private:
+    TBytes end;
+    TBytes begin;
     CDBWrapper db;
     CDBBatch batch;
 };