releases: add TiDB 5.0.0-rc release notes

TOC.md

@@ -528,6 +528,8 @@
 + Release Notes
   + [All Releases](/releases/release-notes.md)
   + [TiDB Roadmap](/roadmap.md)
+  + v5.0
+    + [5.0.0-rc](/releases/release-5.0.0-rc.md)
   + v4.0
     + [4.0.9](/releases/release-4.0.9.md)
     + [4.0.8](/releases/release-4.0.8.md)

releases/release-5.0.0-rc.md

@@ -0,0 +1,62 @@
+---
+title: TiDB 5.0 RC Release Notes
+---
+
+# TiDB 5.0 RC Release Notes
+
+Release date: December 31, 2020
+
+TiDB version: 5.0.0-rc
+
+## New Features
+
++ TiDB
+
+    - Support collation `utf8mb4_unicode_ci` and `utf8_unicode_ci`
+        - [project](https://github.com/pingcap/tidb/issues/17596)
+        - [document](https://docs.pingcap.com/tidb/dev/character-set-and-collation#new-framework-for-collations)
+    - Support error/info log desensitization
+        - [project](https://github.com/pingcap/tidb/issues/18566)
+        - [document](https://github.com/pingcap/tidb/blob/master/errno/logredaction.md)
+    - Support Invisible Indexes
+        - [project](https://github.com/pingcap/tidb/issues/9246)
+        - [document](https://github.com/pingcap/tidb/pull/15366)
+    - Support Async commit. Async Commit is an optimization that reduces commit latency, by returning success to the user when all prewrites have succeeded. (Experimental)
+        - [project](https://github.com/tikv/tikv/projects/34)
+        - [document](https://github.com/pingcap/docs-cn/pull/5181)
+    - Support clustered Index. Clustered indexes provide TiDB the ability to organize tables in a way that can improve the performance of certain queries. (Experimental)
+        - [project](https://github.com/pingcap/tidb/projects/45)
+        - [document](https://docs.pingcap.com/tidb/dev/clustered-indexes)
+    - Support `LIST PARTITION` and `LIST COLUMNS PARTITION` table (Experimental)
+        - [project](https://github.com/pingcap/tidb/issues/20678)
+        - [document](https://docs.pingcap.com/zh/tidb/dev/partitioned-table#list-%E5%88%86%E5%8C%BA) // TODO: use english doc.
+    - Improve the Accuracy and Robustness of Index Selection (Experimental)
+        - [#21817](https://github.com/pingcap/tidb/pull/21817)
+        - [document](https://github.com/pingcap/docs-cn/pull/5164)
+
++ TiKV
+
+    - Support dynamically changing auto-tuned mode of RocksDB rate limiter
+
++ TiFlash
+
+    - Support limiting the memory usage of DeltaIndex
+    - Support limiting the IO write throughput of background data management tasks, to lower the impact of foreground tasks
+
+## Improvements
+
++ TiDB
+
+    - Improve the executor runtime information collection
+        - [issue](https://github.com/pingcap/tidb/issues/18663)
+        - [document](https://docs.pingcap.com/zh/tidb/stable/sql-statement-explain-analyze#explain-analyze)
+    - Optimize the Performance of Bulk Deletion
+        - [issue](https://github.com/pingcap/tidb/issues/18028)
+
++ TiKV
+
+    - Enable compaction guard by default, to split rocksdb SST files at TiKV region boundaries, to reduce overall compaction I/O
+
++ TiFlash
+
+    - Add a thread pool that queues coprocessor tasks, to ease the memory pressure caused by large concurrent coprocessor handling

releases/release-notes.md

@@ -5,6 +5,10 @@ aliases: ['/docs/dev/releases/release-notes/','/docs/dev/releases/rn/']
 
 # TiDB Release Notes
 
+## 5.0
+
+- [5.0.0-rc](/releases/release-5.0.0-rc.md)
+
 ## 4.0
 
 - [4.0.9](/releases/release-4.0.9.md)