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TiDB 3.0.0-rc.2 Release Notes

Release date: May 28, 2019

TiDB version: 3.0.0-rc.2

TiDB Ansible version: 3.0.0-rc.2


On May 28, 2019, TiDB 3.0.0-rc.2 is released. The corresponding TiDB Ansible version is 3.0.0-rc.2. Compared with TiDB 3.0.0-rc.1, this release has greatly improved the stability, usability, features, the SQL optimizer, statistics, and the execution engine.


  • SQL Optimizer

    • Support Index Join in more scenarios #10540
    • Support exporting historical statistics #10291
    • Support the incremental Analyze operation on monotonically increasing index columns #10355
    • Neglect the NULL value in the Order By clause #10488
    • Fix the wrong schema information calculation of the UnionAll logical operator when simplifying the column information #10384
    • Avoid modifying the original expression when pushing down the Not operator #10363
    • Support the dump/load correlation of histograms #10573
  • Execution Engine

    • Handle virtual columns with a unique index properly when fetching duplicate rows in batchChecker #10370
    • Fix the scanning range calculation issue for the CHAR column #10124
    • Fix the issue of PointGet incorrectly processing negative numbers #10113
    • Merge Window functions with the same name to improve execution efficiency #9866
    • Allow the RANGE frame in a Window function to contain no OrderBy clause #10496
  • Server

    • Fix the issue that TiDB continuously creates a new connection to TiKV when a fault occurs in TiKV #10301
    • Make tidb_disable_txn_auto_retry affect all retryable errors instead of only write conflict errors #10339
    • Allow DDL statements without parameters to be executed using prepare/execute #10144
    • Add the tidb_back_off_weight variable to control the backoff time #10266
    • Prohibit TiDB retrying non-automatically committed transactions in default conditions by setting the default value of tidb_disable_txn_auto_retry to on #10266
    • Fix the database privilege judgment of role in RBAC #10261
    • Support the pessimistic transaction mode (experimental) #10297
    • Reduce the wait time for handling lock conflicts in some cases #10006
    • Make the Region cache able to visit follower nodes when a fault occurs in the leader node #10256
    • Add the tidb_low_resolution_tso variable to control the number of TSOs obtained in batches and reduce the times of transactions obtaining TSO to adapt for scenarios where data consistency is not so strictly required #10428
  • DDL

    • Fix the uppercase issue of the charset name in the storage of the old version of TiDB #10272
    • Support preSplit of table partition, which pre-allocates table Regions when creating a table to avoid write hotspots after the table is created #10221
    • Fix the issue that TiDB incorrectly updates the version information in PD in some cases #10324
    • Support modifying the charset and collation using the ALTER DATABASE statement #10393
    • Support splitting Regions based on the index and range of the specified table to relieve hotspot issues #10203
    • Prohibit modifying the precision of the decimal column using the alter table statement #10433
    • Fix the restriction for expressions and functions in hash partition #10273
    • Fix the issue that adding indexes in a table that contains partitions will in some cases cause TiDB panic #10475
    • Validate table information before executing the DDL to avoid invalid table schemas #10464
    • Enable hash partition by default; and enable range columns partition when there is only one column in the partition definition #9936


  • Enable the Region storage by default to store the Region metadata #1524
  • Fix the issue that hot Region scheduling is preempted by another scheduler #1522
  • Fix the issue that the priority for the leader does not take effect #1533
  • Add the gRPC interface for ScanRegions #1535
  • Push operators actively #1536
  • Add the store limit mechanism for separately controlling the speed of operators for each store #1474
  • Fix the issue of inconsistent Config status #1476


  • Engine

    • Support multiple column families sharing a block cache #4563
  • Server

    • Remove TxnScheduler #4098
    • Support pessimistic lock transactions #4698
  • Raftstore

    • Support hibernate Regions to reduce the consumption of the raftstore CPU #4591
    • Fix the issue that the leader does not reply to the ReadIndex requests for the learner #4653
    • Fix transferring leader failures in some cases #4684
    • Fix the dirty read issue in some cases #4688
    • Fix the issue that a snapshot may lose applied data in some cases #4716
  • Coprocessor

    • Add more RPN functions
      • LogicalOr #4691
      • LTReal #4602
      • LEReal #4602
      • GTReal #4602
      • GEReal #4602
      • NEReal #4602
      • EQReal #4602
      • IsNull #4720
      • IsTrue #4720
      • IsFalse #4720
      • Support comparison arithmetic for Int #4625
      • Support comparison arithmetic for Decimal #4625
      • Support comparison arithmetic for String #4625
      • Support comparison arithmetic for Time #4625
      • Support comparison arithmetic for Duration #4625
      • Support comparison arithmetic for Json #4625
      • Support plus arithmetic for Int #4733
      • Support plus arithmetic for Real #4733
      • Support plus arithmetic for Decimal #4733
      • Support MOD functions for Int #4727
      • Support MOD functions for Real #4727
      • Support MOD functions for Decimal #4727
      • Support minus arithmetic for Int #4746
      • Support minus arithmetic for Real #4746
      • Support minus arithmetic for Decimal #4746


  • TiDB Binlog

    • Add a metric to track the delay of data replication downstream #594
  • TiDB Lightning

    • Support merging sharded databases and tables #95
    • Add the retry mechanism for KV write failure #176
    • Update the default value of table-concurrency to 6 #175
    • Reduce required configuration items by automatically discovering tidb.pd-addr and tidb.port if they are not provided #173

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