txn_t *t1 = txn_begin(TXN_READ_WRITE, TXN_REPEATABLE_READ, map);
txn_t *t2 = txn_begin(TXN_READ_WRITE, TXN_REPEATABLE_READ, map);
tm_set(t1, "abc", 2);
txn_t *t1 = txn_begin(TXN_READ_WRITE, TXN_REPEATABLE_READ, map);
txn_t *t2 = txn_begin(TXN_READ_WRITE, TXN_REPEATABLE_READ, map);
tm_set(t1, "abc", 2);