This session will focus on the open-source distributed SQL databases TiDB and YugabyteDB. We will explore their building blocks to understand how they function, highlighting their similarities and architectural differences. Key topics will include how changes are versioned (using either Time Stamp Oracle or Hybrid Logical Clocks), how data is replicated (with Raft), how they store rows, index entries, and transaction intents (utilizing RocksDB LSM trees), and how they implement ACID properties (through either Percolator or IntentsDB).