Together with PingCAP, we tested TiDB 2.1.7 through 3.0.0-rc.2, and found that by default, TiDB violated snapshot isolation, allowing read skew, lost updates, and incompatible orders, thanks to two separate auto-retry mechanisms which blindly re-applied conflicting writes. 3.0.0-rc.2 changed the default settings to provide snapshot isolation by default, as well as fixing a race condition in table creation, and some crashes on startup.