pub unsafe extern "C" fn rocksdb_transactiondb_merge(
    txn_db: *mut rocksdb_transactiondb_t,
    options: *const rocksdb_writeoptions_t,
    key: *const c_char,
    klen: usize,
    val: *const c_char,
    vlen: usize,
    errptr: *mut *mut c_char
)