the ugliest hack ever

leveldb supports prefixing querying , seems mdbx does not
so just write an empty hash value to fake the prefix querying leveldb was doing before

Author: josibake

src/dbwrapper.cpp

@@ -438,7 +438,7 @@ MDBXWrapper::MDBXWrapper(const DBParams& params)
 
     // initialize the mdbx environment.
     DBContext().env = mdbx::env_managed(params.path, DBContext().create_params, DBContext().operate_params);
-    
+
     auto txn = DBContext().env.start_read();
     DBContext().map = txn.open_map(nullptr, mdbx::key_mode::usual, mdbx::value_mode::single);
     txn.commit();

src/node/blockstorage.cpp

@@ -89,6 +89,7 @@ bool BlockTreeDB::WriteBatchSync(const std::vector<std::pair<int, const CBlockFi
     for (const CBlockIndex* bi : blockinfo) {
         batch.Write(std::make_pair(DB_BLOCK_INDEX, bi->GetBlockHash()), CDiskBlockIndex{bi});
     }
+    batch.Write(std::make_pair(DB_BLOCK_INDEX, uint256()), CDiskBlockIndex());
     return m_db->WriteBatch(batch, true);
 }
 
@@ -112,6 +113,9 @@ bool BlockTreeDB::LoadBlockIndexGuts(const Consensus::Params& consensusParams, s
     AssertLockHeld(::cs_main);
     std::unique_ptr<CDBIteratorBase> pcursor(m_db->NewIterator());
     pcursor->Seek(std::make_pair(DB_BLOCK_INDEX, uint256()));
+    // assert(pcursor->Valid());
+    // hack: skip the dummy value and start at the next one
+    if (pcursor->Valid()) pcursor->Next();
 
     // Load m_block_index
     while (pcursor->Valid()) {