Joins

Hash Join Sort-Merge Join

TiDB’s SQL layer currently supports 3 types of distributed join: hash join, sort merge join (when the optimizer thinks even the smallest table is too large to fit in memory and the predicates contain indexed columns, the optimizer would choose sort merge join) and index lookup join.

Query Interface

SQL

Data Model

Key/Value

TiDB uses TiKV as the underlying data storage engine, which uses the Key-Value model and can be seen as a huge distributed ordered Map that is of high performance and reliability.

Stored Procedures

Not Supported

Concurrency Control

Multi-version Concurrency Control (MVCC)

Views

Not Supported

Storage Architecture

Disk-oriented

Isolation Levels

Read Committed Repeatable Read

TiDB uses the Percolator transaction model. A global read timestamp is obtained when the transaction is started, and a global commit timestamp is obtained when the transaction is committed. The execution order of transactions is confirmed based on the timestamps. Repeatable Read is the default transaction isolation level in TiDB.