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TiDB 4.0.15 Release Notes
TiDB 4.0.15 Release Notes: Compatibility changes include bug fixes that might cause upgrade incompatibilities. Feature enhancements for TiKV support changing configurations dynamically. Improvements for TiDB, TiKV, PD, and Tools. Bug fixes for TiDB, TiKV, PD, TiFlash, Backup & Restore, and TiCDC.

TiDB 4.0.15 Release Notes

Release Date: September 27, 2021

TiDB version: 4.0.15

Compatibility changes

  • TiDB

    • Fix the issue that executing SHOW VARIABLES in a new session is slow. This fix reverts some changes made in #21045 and might cause compatibility issues. #24326
    • The following bug fixes change execution results, which might cause upgrade incompatibilities:
      • Fix the issue that greatest(datetime) union null returns empty string #26532
      • Fix the issue that the having clause might not work correctly #26496
      • Fix the wrong execution results that occur when the collations around the between expression are different #27146
      • Fix the result wrong that occurs when the argument of the extract function is a negative duration #27236
      • Fix the wrong execution results that occur when the column in the group_concat function has a non-bin collation #27429
      • Fix the issue that column information is missed when converting the Apply operator to Join #27233
      • Fix the issue of unexpected behavior when casting the invalid string to DATE #26762
      • Fix a bug that the count distinct result on multiple columns is wrong when the new collation is enabled #27091

Feature enhancement

  • TiKV

    • Support changing TiCDC configurations dynamically #10645

Improvements

  • TiDB

    • Trigger auto-analyze based on the histogram row count #24237

  • TiKV

    • Handle read ready and write ready separately to reduce read latency #10475
    • The slow log of TiKV coprocessor only considers the time spent on processing requests. #10841
    • Drop log instead of blocking threads when the slogger thread is overloaded and the queue is filled up #10841
    • Reduce the size of Resolved TS messages to save network bandwidth #2448

  • PD

    • Improve the performance of synchronizing Region information between PDs #3932

  • Tools

    • Backup & Restore (BR)

      • Split and scatter Regions concurrently to improve restore speed #1363
      • Retry BR tasks when encountering the PD request error or the TiKV I/O timeout error #27787
      • Reduce empty Regions when restoring many small tables to avoid affecting cluster operations after the restore #1374
      • Perform the rebase auto id operation while creating tables, which saves the separate rebase auto id DDL operation and speeds up restore #1424

    • Dumpling

      • Filter the skipped databases before getting the table information to improve the filtering efficiency of SHOW TABLE STATUS #337
      • Use SHOW FULL TABLES to get table information for tables to be exported, because SHOW TABLE STATUS cannot work properly in some MySQL versions #322
      • Support backing up MySQL-compatible databases that do not support the START TRANSACTION ... WITH CONSISTENT SNAPSHOT or the SHOW CREATE TABLE syntax #309
      • Refine the Dumpling warning log to avoid the misleading information that a dump fails #340

    • TiDB Lightning

      • Support importing data into tables that have expression index or the index that depends on virtual generated columns #1404

    • TiCDC

      • Always pulls old values from TiKV internally to improve usability #2397
      • Reduce the goroutine usage when a table's Regions are all transferred away from a TiKV node #2284
      • Optimize workerpool for fewer goroutines when concurrency is high #2211
      • Execute DDL statements asynchronously to avoid affecting other changefeeds #2295
      • Add a global gRPC connection pool and share gRPC connections among KV clients #2531
      • Fail fast for unrecoverable DML errors #1724
      • Optimize memory management when the Unified Sorter is using memory to sort data #2553
      • Add Prometheus metrics for DDL executions #2595 #2669
      • Prohibit operating TiCDC clusters across major or minor versions #2601
      • Remove file sorter #2325
      • Clean up changefeed metrics when a changefeed is removed, and clean up processor metrics when a processor exits #2156
      • Optimize the lock-resolving algorithm after a Region is initialized #2188

Bug fixes

  • TiDB

    • Fix a bug that collation is incorrectly set for binary literals when building ranges #23672

    • Fix the "index out of range" error that occurs when a query includes both GROUP BY and UNION #26553

    • Fix the issue that TiDB might fail to send requests if TiKV has tombstone stores #23676 #24648

    • Remove the undocumented /debug/sub-optimal-plan HTTP API #27264

    • Fix the issue of wrong character set and collation for the case when expression #26662

  • TiKV

    • Fix the issue that BR reports the "file already exists" error when TDE is enabled during data restore #1179
    • Fix the potential disk full issue caused by corrupted snapshot files #10813
    • Fix the issue that TiKV deletes stale Regions too frequently #10680
    • Fix the issue that TiKV frequently reconnects the PD client #9690
    • Check stale file information from the encryption file dictionary #9115

  • PD

    • Fix the issue that PD does not fix the down peers in time #4077
    • Fix a bug that PD might panic when scaling out TiKV #3868

  • TiFlash

    • Fix the potential issue of data inconsistency that occurs when TiFlash is deployed on multiple disks
    • Fix a bug of incorrect results that occurs when queries contain filters like CONSTANT, <, <=, >, >=, or COLUMN
    • Fix the issue that the store size in metrics is inaccurate under heavy writing
    • Fix a potential bug that TiFlash cannot restore data when deployed on multiple disks
    • Fix the potential issue that TiFlash cannot garbage-collect the delta data after running for a long time

  • Tools

    • Backup & Restore (BR)

      • Fix a bug that the average speed is inaccurately calculated for backup and restore #1405

    • TiCDC

      • Fix the ErrSchemaStorageTableMiss error that occurs when the DDL Job duplication is encountered in the integrated test #2422
      • Fix a bug that a changefeed cannot be removed if the ErrGCTTLExceeded error occurs #2391
      • Fix the issue that outdated capture might appear in the output of the capture list command #2388
      • Fix the deadlock issue in the TiCDC processor #2017
      • Fix a data inconsistency issue that occurs because multiple processors might write data to the same table when this table is being re-scheduled #2230
      • Fix a bug that the EtcdWorker snapshot isolation is violated in metadata management #2557
      • Fix the issue that the changefeed cannot be stopped due to the DDL sink error #2552
      • Fix the issue of TiCDC Open Protocol: TiCDC outputs an empty value when there is no change in a transaction #2612
      • Fix a bug that causes TiCDC to panic on the unsigned TINYINT type #2648
      • Decrease the gRPC window size to avoid the OOM that occurs when TiCDC captures too many Regions #2202
      • Fix the OOM issue that occurs when TiCDC captures too many Regions #2673
      • Fix the issue of process panic that occurs when encoding the data types such as mysql.TypeString, mysql.TypeVarString, mysql.TypeVarchar into JSON #2758
      • Fix the a memory leak issue that might occur when creating a new changefeed #2389
      • Fix a bug that DDL handling fails when a changefeed starts at the finish TS of a schema change #2603
      • Fix the issue of potential DDL loss when the owner crashes when executing DDL statements #1260
      • Fix the issue of insecure concurrent access to the map in SinkManager #2298