title	category
TiDB RC4 Release Notes	releases

TiDB RC4 Release Notes

On August 4, 2017, TiDB RC4 is released! This release is focused on MySQL compatibility, SQL optimization, stability, and performance.

Highlight:

For performance, the write performance is improved significantly, and the computing task scheduling supports prioritizing to avoid the impact of OLAP on OLTP.
The optimizer is revised for a more accurate query cost estimating and for an automatic choice of the Join physical operator based on the cost.
Many enhancements have been introduced to be more compatible with MySQL.
TiSpark is now released to better support the OLAP business scenarios. You can now use Spark to access the data in TiKV.

The SQL query optimizer refactoring:
- Better support for TopN queries
- Support the automatic choice of the of the Join physical operator based on the cost
- Improved Projection Elimination
The version check of schema is based on Table to avoid the impact of DDL on the ongoing transactions
Support BatchIndexJoin
Improve the Explain statement
Improve the Index Scan performance
Many enhancements have been introduced to be more compatible with MySQL
Support the JSON type and operations
Support the configuration of query prioritizing and isolation level

Support using PD to set the TiKV location labels
Optimize the scheduler
- PD is now supported to initialize the scheduling commands to TiKV.
- Accelerate the response speed of the region heartbeat.
- Optimize the balance algorithm
Optimize data loading to speed up failover