TiDB 4.0 RC Release Notes

Release date: April 8, 2020

TiDB version: 4.0.0-rc

TiUP version: 0.0.3

Warning:

Some known issues are found in this version, and these issues are fixed in new versions. It is recommended that you use the latest 4.0.x version.

Compatibility Changes

• TiDB

  • Refuse to get started instead of returning an alert log when the tidb-server status port is occupied #15177

• TiKV

  • Support the pipelined feature in pessimistic transactions, which improves the TPC-C performance by 20%. The risk is that the transaction commit might fail because of lock failure during the execution #6984
  • Enable the unify-read-pool configuration item in new clusters by default and use the previous setting of this item in old clusters #7059

• Tools

  • TiDB Binlog

    • Add the configuration item for verifying Common Name #934

Important Bug Fixes

• TiDB

  • Fix the issue that replication between the upstream and downstream might go wrong when the DDL job is executed using the PREPARE statement because of the incorrect job query in the internal records #15435
  • Fix the issue of incorrect subquery result in the Read Commited isolation level #15471
  • Fix the issue of incorrect results caused by the Inline Projection optimization #15411
  • Fix the issue that the SQL Hint INL_MERGE_JOIN is executed incorrectly in some cases #15515
  • Fix the issue that columns with the AutoRandom attribute are rebased when the negative number is explicitly written to these columns #15397

New Features

• TiDB

  • Add the case-sensitive collation so that users can enable utf8mb4_general_ci and utf8_general_ci in a new cluster #33
  • Enhance the RECOVER TABLE syntax to support recovering truncated tables #15398
  • Refuse to get started instead of returning an alert log when the the tidb-server status port is occupied #15177
  • Optimize the write performance of using a sequence as the default column values #15216
  • Add the DDLJobs system table to query the details of DDL jobs #14837
  • Optimize the aggFuncSum performance #14887
  • Optimize the output of EXPLAIN #15507

• TiKV

  • Support the pipelined feature in pessimistic transactions, which improves the TPC-C performance by 20%. The risk is that the transaction commit might fail because of lock failure during the execution #6984
  • Support TLS in the HTTP port #5393
  • Enable the unify-read-pool configuration item in new clusters by default and use the previous setting of this item in old clusters #7059

• PD

  • Support getting the default PD configuration information through the HTTP API #2258

• Tools

  • TiDB Binlog

    • Add the configuration item for verifying Common Name #934

  • TiDB Lightning

    • Optimize the performance of TiDB Lightning #281 #275

Bug Fixes

• TiDB

  • Fix the issue that replication between the upstream and downstream might go wrong when the DDL job is executed using the PREPARE statement because of the incorrect job query in the internal records #15435
  • Fix the issue of incorrect subquery result in the Read Commited isolation level #15471
  • Fix the issue of possible wrong behavior when using INSERT ... VALUES to specify the BIT(N) data type #15350
  • Fix the issue that the DDL Job internal retry does not fully achieve the expected outcomes because the values of ErrorCount fail to be summed correctly #15373
  • Fix the issue that Garbage Collection might work abnormally when TiDB connects to TiFlash #15505
  • Fix the issue of incorrect result caused by the Inline Projection optimization #15411
  • Fix the issue that the SQL Hint INL_MERGE_JOIN is executed incorrectly in some cases #15515
  • Fix the issue that columns with the AutoRandom attribute are rebased when the negative number is explicitly written to these columns #15397

• TiKV

  • Fix the possible panic caused by transferring the leader when the Follower Read feature is enabled #7101

• Tools

  • TiDB Lightning

    • Fix the issue of data error caused by the error of character conversion when the backend is TiDB #283

  • TiCDC

    • Fix the issue that an error is returned if the test schema does not exist in the downstream when MySQL sink is executing the DDL statement #353
    • Support the real-time interactive mode in CDC cli #351
    • Support checking whether the table in the upstream can be replicated during data replication #368
    • Support asynchronous write to Kafka #344