TiDB 4.0 RC.1 Release Notes

Release date: April 28, 2020

TiDB version: 4.0.0-rc.1

Compatibility Changes

• TiKV

  • Disable the Hibernate Region feature by default #7618

• TiDB Binlog

  • Support the sequence DDL operation in Drainer #950

Important Bug Fixes

• TiDB

  • Fix the issue that the INSERT ... ON DUPLICATE UPDATE statement might be incorrectly executed on multiple rows in an explicit transaction because MemBuffer is not checked #16689
  • Fix the data inconsistency when locking duplicated keys on multiple rows #16769
  • Fix the panic that occurs when recycling the non-superbatch idle connection between TiDB instances #16303

• TiKV

  • Fix the deadlock issue caused by the probe request from TiDB #7540
  • Fix the issue that the minimum commit timestamp of a transaction might overflow which affects data correctness #7638

• TiFlash

  • Fix the data loss issue caused by the rename table operation when multiple data paths are configured
  • Fix the issue that an error occurs when reading data from a merged Region
  • Fix the issue that an error occurs when reading data from a Region that is in the abnormal state
  • Modify the mapping of table names in TiFlash to correctly support recover table/flashback table
  • Modify the storage path to fix the potential data loss issue that occurs when renaming the table
  • Fix the potential panic of TiDB when Super Batch is enabled
  • Modify the read mode in the online update scenario to improve the read performance

• TiCDC

  • Fix the replication failure that occurs because the schema internally maintained in TiCDC fails to correctly handle the timing issue of read and write operations #438 #450 #478 #496
  • Fix the bug that the TiKV client fails to correctly maintain the internal resources when encountering some TiKV anomalies #499 #492
  • Fix the bug that meta data is not correctly cleaned up and abnormally remains in the TiCDC nodes #488 #504
  • Fix the issue that the TiKV client fails to correctly handle the repeated sending of the prewrite event #446
  • Fix the issue that the TiKV client fails to correctly handle the redundant prewrite events received before the initialization #448

• Backup & Restore (BR)

  • Fix the issue that checksum is still executed when checksum is disabled #223
  • Fix the incremental replication failure when auto-random or alter-pk is enabled in TiDB #230 #231

New Features

• TiDB

  • Support sending Coprocessor requests to TiFlash in batches #16226
  • Enable the Coprocessor cache feature by default #16710
  • Parse only the registered sections of a statement in the special comment of the SQL statement #16157
  • Support using the SHOW CONFIG syntax to show the configurations of PD and TiKV instances #16475

• TiKV

  • Support using the user-owned KMS key for the server-side encryption when backing up data to S3 #7630
  • Enable the load-based split region operation #7623
  • Support validating common names #7468
  • Add the file lock check to avoid starting multiple TiKV instances that are bound to the same address #7447
  • Support AWS KMS in encryption at rest #7465

• Placement Driver (PD)

  • Remove config manager to let other components control their component configurations #2349

• TiFlash

  • Add the metrics report related to the read and write workloads of DeltaTree engine
  • Cache the handle and version columns to reduce the disk I/O of a single read or write request
  • Support pushing down the fromUnixTime and dateFormat functions
  • Evaluate the global state according to the first disk and report this evaluation
  • Add the graphics in Grafana related to the read and write workloads of DeltaTree engine
  • Optimize the decimal data encoding in the Chunk codec
  • Implement the gRPC API of Diagnostics (SQL diagnosis) to support querying system tables such as INFORMATION_SCHEMA.CLUSTER_INFO

• TiCDC

  • Support sending messages in batches in the Kafka sink module #426
  • Support file sorting in the processor #477
  • Support automatic resolve lock #459
  • Add the feature that automatically updates the TiCDC service GC safe point to PD #487
  • Add the timezone setting for data replication #498

• Backup and Restore (BR)

  • Support configuring S3/GCS in the storage URL #246

Bug Fixes

• TiDB

• Fix the issue that negative numbers cannot be correctly displayed in the system table because the columns are defined as unsigned #16004
• Add a warning when the use_index_merge hint contains the invalid index name #15960
• Forbid multiple instances of a TiDB server sharing the same temporary directory #16026
• Fix the panic that occurs during the execution of explain for connection when the plan cache is enabled #16285
• Fix the issue that the result of the tidb_capture_plan_baselines system variable is incorrectly displayed #16048
• Fix the issue that the group by clause in the prepare statement is incorrectly parsed #16377
• Fix the panic that might occur during the execution of the analyze primary key statement #16081
• Fix the issue that the TiFlash store information in the cluster_info system table is wrong #16024
• Fix the panic that might occur during the Index Merge process #16360
• Fix the issue that an incorrect result might occur when the Index Merge reader reads the generated columns #16359
• Fix the incorrect display of the default sequence value in the show create table statement #16526
• Fix the issue that the not-null error is returned because the sequence is used as the default values of the primary key #16510
• Fix the issue that no error is reported for a blocked SQL execution when TiKV continues to return the StaleCommand error #16530
• Fix the issue that an error is reported if you only specify COLLATE when creating a database; add the missing COLLATE part in the result of SHOW CREATE DATABASE #16540
• Fix the partition pruning failure when the plan cache is enabled #16723
• Fix the bug that PointGet returns wrong results when handling the overflow #16755
• Fix the issue that a wrong result is returned when querying the slow_query system table with equal time values #16806

• TiKV

  • Address the OpenSSL security issue: CVE-2020-1967 #7622
  • Avoid protecting rollback records written by BatchRollback to improve performance when many write conflicts exist in optimistic transactions #7604
  • Fix the issue that the needless wake-up of transactions results in useless retry and performance reduction in heavy lock-race workloads #7551
  • Fix the issue that the Region might be stuck in the multi-time merging #7518
  • Fix the issue that the learner is not deleted when deleting the learner #7518
  • Fix the issue that follower read might cause panic in raft-rs #7408
  • Fix the bug that a SQL operation might fail because of the group by constant error #7383
  • Fix the issue that an optimistic lock might block reads if the corresponding primary lock is a pessimistic lock #7328

• PD

  • Fix the issue that some APIs might fail in the TLS validation #2363
  • Fix the issue that the configuration API cannot accept a configuration item with a prefix #2354
  • Fix the issue that the 500 error is returned when the scheduler is not found #2328
  • Fix the issue that the 404 error is returned for the scheduler config balance-hot-region-scheduler list command #2321

• TiFlash

  • Disable the coarse-grained index optimization for the storage engine
  • Fix the bug that an exception is thrown when resolving locks for Regions and some locks need to be skipped
  • Fix the null pointer exception (NPE) when collecting the Coprocessor statistics
  • Fix the check for Region meta to ensure that the process of Region Split/Region Merge is correct
  • Fix the issue that the message size exceeds the limit for gRPC because the size of Coprocessor response is not estimated
  • Fix the handling of the AdminCmdType::Split command in TiFlash