releases, readme: add the release notes for 2.1 beta

README.md

@@ -130,6 +130,7 @@
 - [Frequently Asked Questions (FAQ)](FAQ.md)
 - [TiDB Best Practices](https://pingcap.github.io/blog/2017/07/24/tidbbestpractice/)
 + [Releases](releases/rn.md)
+  - [2.1 Beta](releases/21beta.md)
   - [2.0.4](releases/204.md)
   - [2.0.3](releases/203.md)
   - [2.0.2](releases/202.md)

releases/21beta.md

@@ -0,0 +1,85 @@
+---
+title: TiDB 2.1 Beta Release Notes
+category: Releases
+---
+
+# TiDB 2.1 Beta Release Notes
+
+On June 29, 2018, TiDB 2.1 Beta is released! Compared with TiDB 2.0, this release has great improvement in stability, SQL optimizer, statistics information, and execution engine.
+
+## TiDB
+
+- SQL Optimizer
+    - Optimize the selection range of `Index Join` to improve the execution performance
+    - Optimize correlated subquery, push down `Filter`, and extend the index range, to improve the efficiency of some queries by orders of magnitude
+    - Support `Index Hint` and `Join Hint` in the `UPDATE` and `DELETE` statements
+    - Validate Hint `TIDM_SMJ` when no available index exists
+    - Support pushdown of the `ABS`, `CEIL`, `FLOOR`, `IS TRUE`, and `IS FALSE` functions
+    - Handle the `IF` and `IFNULL` functions especially in the constant folding process
+- SQL Execution Engine
+    - Implement parallel `Hash Aggregate` operators and improve the computing performance of `Hash Aggregate` by 350% in some scenarios
+    - Implement parallel `Project` operators and improve the performance by 74% in some scenarios 
+    - Read the data of the `Inner` table and `Outer` table of `Hash Join` concurrently to improve the execution performance
+    - Fix incorrect results of `INSERT … ON DUPLICATE KEY UPDATE …` in some scenarios
+    - Fix incorrect results of the `CONCAT_WS`, `FLOOR`, `CEIL`, and `DIV` built-in functions
+- Server
+    - Add the HTTP API to scatter the distribution of table Regions in the TiKV cluster
+    - Add the `auto_analyze_ratio` system variable to control the threshold value of automatic `Analyze` 
+    - Add the HTTP API to control whether to open the general log
+    - Add the HTTP API to modify the log level online
+    - Add the user information in the general log and the slow query log
+    - Support the server side cursor
+- Compatibility
+    - Support more MySQL syntax
+    - Make the `bit` aggregate function support the `ALL` parameter
+    - Support the `SHOW PRIVILEGES` statement
+- DML
+    - Decrease the memory usage of the `INSERT INTO SELECT` statement 
+    - Fix the performance issue of `PlanCache`
+    - Add the `tidb_retry_limit` system variable to control the automatic retry times of transactions
+    - Add the `tidb_disable_txn_auto_retry` system variable to control whether the transaction tries automatically
+    - Fix the accuracy issue of the written data of the `time` type
+    - Support the queue of locally conflicted transactions to optimize the conflicted transaction performance
+    - Fix `Affected Rows` of the `UPDATE` statement 
+    - Optimize the statement performance of `insert ignore on duplicate key update`
+- DDL
+    - Optimize the execution speed of the `CreateTable` statement
+    - Optimize the execution speed of `ADD INDEX` and improve it greatly in some scenarios
+    - Fix the issue that the number of added columns by `Alter table add column` exceeds the limit of the number of table columns 
+    - Fix the issue that DDL job retries lead to an increasing pressure on TiKV in abnormal conditions
+    - Fix the issue that TiDB continuously reloads the schema information in abnormal conditions
+    - Do not output the `FOREIGN KEY` related information in the result of `SHOW CREATE TABLE`
+    - Support the `select tidb_is_ddl_owner()` statement to facilitate judging whether TiDB is `DDL Owner`
+    - Fix the issue that the index is deleted in the `Year` type in some scenarios
+    - Fix the renaming table issue in the concurrent execution scenario
+    - Support the `AlterTableForce` syntax
+    - Support the `AlterTableRenameIndex` syntax with `FromKey` and `ToKey`
+    - Add the table name and database name in the output information of `admin show ddl jobs`
+
+## PD
+
+- Enable Raft PreVote between PD nodes to avoid leader reelection when network recovers after network isolation
+- Optimize the issue that Balance Scheduler schedules small Regions frequently
+- Optimize the hotspot scheduler to improve its adaptability in traffic statistics information jitters
+- Skip the Regions with a large number of rows when scheduling `region merge` 
+- Enable `raft learner` by default to lower the risk of unavailable data caused by machine failure during scheduling
+- Remove `max-replica` from `pd-recover`
+- Add `Filter` metrics
+- Fix the issue that Region information is not updated after tikv-ctl unsafe recovery
+- Fix the issue that TiKV disk space is used up caused by replica migration in some scenarios
+- Compatibility notes
+    - Do not support rolling back to v2.0.x or earlier due to update of the new version storage engine
+    - Enable `raft learner` by default in the new version of PD. If the cluster is upgraded from 1.x to 2.1, the machine should be stopped before upgrade or a rolling update should be first applied to TiKV and then PD 
+
+
+## TiKV
+
+- Upgrade Rust to the `nightly-2018-06-14` version
+- Enable `Raft PreVote` to avoid leader reelection generated when network recovers after network isolation
+- Add a metric to display the number of files and `ingest` related information in each layer of RocksDB
+- Print `key` with too many versions when GC works
+- Use `static metric` to optimize multi-label metric performance (YCSB `raw get` is improved by 3%)
+- Remove `box` in multiple modules and use patterns to improve the operating performance (YCSB `raw get` is improved by 3%)
+- Use `asynchronous log` to improve the performance of writing logs 
+- Add a metric to collect the thread status
+- Decease memory copy times by decreasing `box` used in the application to improve the performance

releases/rn.md

@@ -5,6 +5,7 @@ category: release
 
 # TiDB Release Notes
 
+  - [2.1 Beta](21beta.md)
   - [2.0.4](204.md)
   - [2.0.3](203.md)
   - [2.0.2](202.md)