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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.


  • 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


  • 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


  • 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

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