TiDB 5.1.2 Release Notes

Release Date: September 27, 2021

TiDB version: 5.1.2

Compatibility changes

TiDB
- 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 wrong execution results that occur when the column in the group_concat function has a non-bin collation #27429
  - Fix an issue that using a count(distinct) expression on multiple columns returns wrong result when the new collation is enabled #27091
  - Fix the result wrong that occurs when the argument of the extract function is a negative duration #27236
  - Fix the issue that inserting an invalid date does not report an error when the SQL_MODE is 'STRICT_TRANS_TABLES' #26762
  - Fix the issue that using an invalid default date does not report an error when the SQL_MODE is 'NO_ZERO_IN_DATE' #26766
Tools
- TiCDC
  - Set the compatible version from 5.1.0-alpha to 5.2.0-alpha #2659

Improvements

TiDB
- Trigger auto-analyze by histogram row count and increase the accuracy of this trigger action #24237
TiKV
- Support dynamically modifying TiCDC configurations #10645
- Reduce the size of Resolved TS message to save network bandwidth #2448
- Limit the counts of peer stats in the heartbeat message reported by a single store #10621
PD
- Allow empty Regions to be scheduled and use a separate tolerance configuration in scatter range scheduler #4117
- Improve the performance of synchronizing Region information between PDs #3933
- Support dynamically adjusting the retry limit of a store based on the generated operator #3744
TiFlash
- Support the DATE() function
- Add Grafana panels for write throughput per instance
- Optimize the performance of the leader-read process
- Accelerate the process of canceling MPP tasks
Tools
- TiCDC
  - Optimize memory management when the Unified Sorter is using memory to sort data #2553
  - Optimize workerpool for fewer goroutines when concurrency is high #2211
  - Reduce goroutine usage when a table's Region transfer away from a TiKV node #2284
  - Add a global gRPC connection pool and share gRPC connections among KV clients #2534
  - Prohibit operating TiCDC clusters across major and minor versions #2599
- Dumpling
  - Support backing up MySQL-compatible databases that do not support START TRANSACTION ... WITH CONSISTENT SNAPSHOT and SHOW CREATE TABLE #309

Bug fixes

TiDB
- Fix the potential wrong results of index hash join when the hash column is the ENUM type #27893
- Fix a batch client bug that recycle idle connection might block sending requests in some rare cases #27678
- Fix the issue that the overflow check of the FLOAT64 type is different with that of MySQL #23897
- Fix the issue that TiDB returns an unknow error while it should return the pd is timeout error #26147
- Fix the wrong character set and collation for the case when expression #26662
- Fix the potential can not found column in Schema column error for MPP queries #28148
- Fix a bug that TiDB might panic when TiFlash is shutting down #28096
- Fix the issue of wrong range caused by using enum like 'x%' #27130
- Fix the Common Table Expression (CTE) dead lock issue when used with IndexLookupJoin #27410
- Fix a bug that retryable deadlocks are incorrectly recorded into the INFORMATION_SCHEMA.DEADLOCKS table #27400
- Fix the issue that the TABLESAMPLE query result from partitioned tables is not sorted as expected #27349
- Remove the unused /debug/sub-optimal-plan HTTP API #27265
- Fix a bug that the query might return wrong results when the hash partitioned table deals with unsigned data #26569
- Fix a bug that creating partition fails if NO_UNSIGNED_SUBTRACTION is set #26765
- Fix the issue that the distinct flag is missing when Apply is converted to Join #26958
- Set a block duration for the newly recovered TiFlash node to avoid blocking queries during this time #26897
- Fix a bug that might occur when the CTE is referenced more than once #26212
- Fix a CTE bug when MergeJoin is used #25474
- Fix a bug that the SELECT FOR UPDATE statement does not correctly lock the data when a normal table joins a partitioned table #26251
- Fix the issue that the SELECT FOR UPDATE statement returns an error when a normal table joins a partitioned table #26250
- Fix the issue that PointGet does not use the lite version of resolving lock #26562
TiKV
- Fix a panic issue that occurs after TiKV is upgraded from v3.x to later versions #10902
- Fix the potential disk full issue caused by corrupted snapshot files #10813
- Make the slow log of TiKV coprocessor only consider 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
- Fix a panic issue that occurs when processing Coprocessor requests times out #10852
- Fix the TiKV panic issue that occurs when upgrading from a pre-5.0 version with Titan enabled #10842
- Fix the issue that TiKV of a newer version cannot be rolled back to v5.0.x #10842
- Fix the issue that TiKV might delete files before ingesting data to RocksDB #10438
- Fix the parsing failure caused by the left pessimistic locks #26404
PD
- Fix the issue that PD does not fix the down peers in time #4077
- Fix the issue that the replica count of the default placement rules stays constant after replication.max-replicas is updated #3886
- Fix a bug that PD might panic when scaling out TiKV #3868
- Fix a bug that the hot Region scheduler cannot work when the cluster has the evict leader scheduler #3697
TiFlash
- Fix the issue of unexpected results when TiFlash fails to establish MPP connections
- Fix the potential issue of data inconsistency that occurs when TiFlash is deployed on multiple disks
- Fix a bug that MPP queries get wrong results when TiFlash server is under high load
- Fix a potential bug that MPP queries hang forever
- Fix the panic issue when operating store initialization and DDL simultaneously
- Fix a bug of incorrect results that occurs when queries contain filters like CONSTANT, <, <=, >, >=, or COLUMN
- Fix the potential panic issue when Snapshot is applied simultaneously with multiple DDL operations
- Fix the issue that the store size in metrics is inaccurate under heavy writing
- Fix the potential issue that TiFlash cannot garbage-collect the delta data after running for a long time
- Fix the issue of wrong results when the new collation is enabled
- Fix the potential panic issue that occurs when resolving locks
- Fix a potential bug that metrics display wrong values
Tools
- Backup & Restore (BR)
  - Fix the issue that the average speed is not accurate during data backup and restore #1405
- Dumpling
  - Fix the issue that Dumpling is pending when show table status returns incorrect results in some MySQL versions (8.0.3 and 8.0.23) #322
  - Fix the CLI compatibility issue with 4.0.x clusters on the default sort-engine option #2373
- TiCDC
  - Fix a bug that the JSON encoding might cause panic when processing a string type value that is string or []byte #2758
  - Reduce gRPC window size to avoid OOM #2673
  - Fix a gRPC keepalive error under high memory pressure #2202
  - Fix a bug that an unsigned tinyint causes TiCDC to panic #2648
  - Fix an empty value issue in TiCDC Open Protocol. An empty value is no longer output when there is no change in one transaction. #2612
  - Fix a bug in DDL handling during manual restarts #2603
  - Fix the issue that EtcdWorker's snapshot isolation might be wrongly violated when managing the metadata #2559
  - Fix a bug that multiple processors might write data to the same table when TiCDC is rescheduling the table #2230
  - Fix a bug that changefeed might be reset unexpectedly when TiCDC gets the ErrSchemaStorageTableMiss error #2422
  - Fix a bug that changefeed cannot be removed when TiCDC gets the ErrGCTTLExceeded error #2391
  - Fix a bug that TiCDC fails to synchronize large tables to cdclog #1259 #2424