Libbitcoin Blockchain

The libbitcoin-blockchain library is a dependency of libbitcoin-node and libbitcoin-server. It was originally contained within libbitcoin.

Example

#include <string>
#include <bitcoin/blockchain.hpp>

// Initialize the blockchain
int main(int argc, char* argv[])
{
    std::string prefix("blockchain");
    
    if (argc > 1)
        prefix = argv[1];
       
    bc::chain::initialize_blockchain(prefix);
    bc::chain::db_paths paths(prefix);
    
    constexpr size_t history_height = 0;
    bc::chain::db_interface interface(paths, { history_height });
    interface.start();
    const auto genesis = bc::genesis_block();
    interface.push(genesis);
    
    return 0;
}

Design

The original implementation used LevelDB. Following a redesign in late 2014 by Amir Taaki (genjix) the database was replaced by a memory-mapped I/O implementation. Logical queries are performed using a set of hash tables. The number of hash buckets is optimized to minimize hash collisions, though collisions are accommodated. These changes resulted in a substantial performance increase, near constant time, for queries against the blockchain. Insert performance was not materially affected.

Database

The following files constitute the blockchain database non-volatile storage. As of height 350,000 the database consumes approximately 105 GB of disk space.

• blocks_lookup
• blocks_rows
• history_lookup
• history_rows
• spends
• stealth_index
• stealth_rows
• txs

Consensus Validation

By default the library depends on the libbitcoin-consensus library. This ensures that consensus checks are identical to those implemented by bitcoind. By building using the --without-consensus flag the dependency is avoided and libbitcoin native consensus checks are used instead.

Considerations

• There is no mechanical hard drive optimization. The implementation is intended for solid state drives (SSD).
• There is a possibility of index corruption during hard shutdown. There is no means of detecting corruption aside from catastrophic fault. However given that the entire blockchain is a cache this is not considered significant. Repair can be accomplished by re-synchronizing the blockchain.
• Data files are append only, with logical deletions only. Therefore file size is not minimized following blockchain reorganization although the impact is typically small. Defragmentation can be accomplished by re-synchronizing the blockchain.
• The database is effectively locked during write operations. As these operations are anticipated on a period of approximately ten minutes this is not typically significant. However during a period of catch-up synchronizing the server can become continuously unresponsive to requests.

Dependencies

• boost
• libsecp256k1
• libbitcoin-consensus (optional)

See Also

• Libbitcoin