releases: add the release notes for 2.0 RC1 (pingcap#367)

Author: lilin90

releases/2rc1.md

@@ -0,0 +1,39 @@
+---
+title: TiDB 2.0 RC1 Release Notes
+category: Releases
+---
+
+# TiDB 2.0 RC1 Release Notes
+
+On March 9, 2018, TiDB 2.0 RC1 is released. This release has great improvement in MySQL compatibility, SQL optimization and stability.
+
+## TiDB:
+
+- Support limiting the memory usage by a single SQL statement, to reduce the risk of OOM
+- Support pushing the Stream Aggregate operator down to TiKV
+- Support validating the configuration file
+- Support obtaining the information of TiDB configuration through HTTP API
+- Compatible with more MySQL syntax in Parser
+- Improve the compatibility with Navicat
+- Improve the optimizer and extract common expressions with multiple OR conditions, to choose better query plan
+- Improve the optimizer and convert subqueries to Join operators in more scenarios, to choose better query plan
+- Resolve Lock in the Batch mode to increase the garbage collection speed
+- Fix the length of Boolean field to improve compatibility
+- Optimize the Add Index operation and give lower priority to all write and read operations, to reduce the impact on online business
+
+## PD:
+
+- Optimize the logic of code used to check the Region status to improve performance
+- Optimize the output of log information in abnormal conditions to facilitate debugging
+- Fix the monitor statistics that the disk space of TiKV nodes is not enough
+- Fix the wrong reporting issue of the health interface when TLS is enabled
+- Fix the issue that concurrent addition of replicas might exceed the threshold value of configuration, to improve stability 
+
+## TiKV:
+
+- Fix the issue that gRPC call is not cancelled when PD leaders switch
+- Protect important configuration which cannot be changed after initial configuration
+- Add gRPC APIs used to obtain metrics
+- Check whether SSD is used when you start the cluster
+- Optimize the read performance using ReadPool, and improve the performance by 30% in the `raw get` test
+- Improve metrics and optimize the usage of metrics

releases/rn.md

@@ -5,6 +5,7 @@ category: release
 
 # TiDB Release Notes
 
+  - [2.0 RC1](2rc1.md)
   - [1.1 Beta](11beta.md)
   - [1.0.8](108.md)
   - [1.0.7](107.md)