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TiDB 5.0.4 Release Notes
Compatibility changes include fixes for slow `SHOW VARIABLES` execution, default value change for `tidb_stmt_summary_max_stmt_count`, and bug fixes that may cause upgrade incompatibilities. Feature enhancements include support for setting `tidb_enforce_mpp=1` and dynamic TiCDC configurations. Improvements cover auto-analyze trigger, MPP query retry support, and stable result mode. Bug fixes address various issues in TiDB, TiKV, PD, TiFlash, and tools like Dumpling and TiCDC.

TiDB 5.0.4 Release Notes

Release Date: September 27, 2021

TiDB version: 5.0.4

Compatibility changes

  • TiDB

    • Fix the issue that executing SHOW VARIABLES in a new session is slow. This fix reverts some changes made in #19341 and might cause compatibility issues. #24326
    • Change the default value of the tidb_stmt_summary_max_stmt_count variable from 200 to 3000 #25873
    • The following bug fixes change execution results, which might cause upgrade incompatibilities:
      • Fix the issue that TiDB returns wrong result when the children of UNION contain the NULL value #26559
      • Fix the issue that greatest(datetime) union null returns empty string #26532
      • Fix the issue that the behavior of the last_day function is incompatible in SQL mode #26000
      • 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
      • Fix a bug on the query range of prefix index #26029
      • Fix the issue that the LOAD DATA statement might abnormally import non-utf8 data #25979
      • Fix the issue that insert ignore on duplicate update might insert wrong data when the secondary index has the same column with the primary key #25809
      • Fix the issue that insert ignore duplicate update might insert wrong data when a partitioned table has a clustered index #25846
      • Fix the issue that the query result might be wrong when the key is the ENUM type in point get or batch point get #24562
      • Fix the wrong result that occurs when dividing a BIT-type value #23479
      • Fix the issue that the results of prepared statements and direct queries might be inconsistent #22949
      • Fix the issue that the query result might be wrong when a YEAR type is compared with a string or an integer type #23262

Feature enhancements

  • TiDB

    • Support setting tidb_enforce_mpp=1 to ignore the optimizer estimation and forcibly use the MPP mode #26382

  • TiKV

    • Support changing TiCDC configurations dynamically #10645

  • PD

    • Add OIDC-based SSO support for TiDB Dashboard #3884

  • TiFlash

    • Support the HAVING() function in DAG requests
    • Support the DATE() function
    • Add Grafana panels for write throughput per instance

Improvements

  • TiDB

    • Trigger auto-analyze based on the histogram row count #24237
    • Stop sending requests to a TiFlash node for a period if the node has failed and restarted before #26757
    • Increase the split region upper limit to make split table and presplit more stable #26657
    • Support retry for MPP queries #26483
    • Check the availability of TiFlash before launching MPP queries #1807
    • Support the stable result mode to make the query result more stable #26084
    • Support the MySQL system variable init_connect and its associated features #18894
    • Thoroughly push down the COUNT(DISTINCT) aggregation function in the MPP mode #25861
    • Print log warnings when the aggregation function cannot be pushed down in EXPLAIN statements #25736
    • Add error labels for TiFlashQueryTotalCounter in Grafana dashboard #25327
    • Support getting the MVCC data of a clustered index table through a secondary index by HTTP API #24209
    • Optimize the memory allocation of prepared statement in parser #24371

  • TiKV

    • Handle read ready and write ready separately to reduce read latency #10475
    • Reduce the size of Resolved TS messages to save network bandwidth #2448
    • Drop log instead of blocking threads when the slogger thread is overloaded and the queue is filled up #10841
    • Make the slow log of TiKV coprocessor only consider the time spent on processing requests #10841
    • Make prewrite as idempotent as possible to reduce the chance of undetermined errors #10587
    • Avoid the false "GC can not work" alert under low write flow #10662
    • Make the database to be restored always match the original cluster size during backup. #10643
    • Ensure that the panic output is flushed to the log #9955

  • PD

    • Improve the performance of synchronizing Region information between PDs #3993

  • Tools

    • Dumpling

      • Support backing up MySQL-compatible databases that do not support the START TRANSACTION ... WITH CONSISTENT SNAPSHOT or the SHOW CREATE TABLE syntax #309

    • TiCDC

      • Optimize memory management when Unified Sorter is using memory to sort #2553
      • Prohibit operating TiCDC clusters across major or minor versions #2598
      • Reduce the goroutine usage when a table's Regions are all transferred away from a TiKV node #2284
      • Remove file sorter #2326
      • Always pull the old values from TiKV and the output is adjusted according to enable-old-value #2301
      • Improve the error message returned when a PD endpoint misses the certificate #1973
      • Optimize workerpool for fewer goroutines when concurrency is high #2211
      • Add a global gRPC connection pool and share gRPC connections among KV clients #2533

Bug Fixes

  • TiDB

    • Fix the issue that TiDB might panic when querying a partitioned table and the partition key has the IS NULL condition #23802
    • Fix the issue that the overflow check of the FLOAT64 type is different with that of MySQL #23897
    • Fix the wrong character set and collation for the case when expression #26662
    • Fix the issue that committing pessimistic transactions might cause write conflicts #25964
    • Fix a bug that the index keys in a pessimistic transaction might be repeatedly committed #26359 #10600
    • Fix the issue that TiDB might panic when resolving the async commit locks #25778
    • Fix a bug that a column might not be found when using INDEX MERGE #25045
    • Fix a bug that ALTER USER REQUIRE SSL clears users' authentication_string #25225
    • Fix a bug that the value of the tidb_gc_scan_lock_mode global variable on a new cluster shows "PHYSICAL" instead of the actual default mode "LEGACY" #25100
    • Fix the bug that the TIKV_REGION_PEERS system table does not show the correct DOWN status #24879
    • Fix the issue of memory leaks that occurs when HTTP API is used #24649
    • Fix the issue that views do not support DEFINER #24414
    • Fix the issue that tidb-server --help exits with the code 2 #24046
    • Fix the issue that setting the global variable dml_batch_size does not take effect #24709
    • Fix the issue that using read_from_storage and partitioned table at the same time causes an error #20372
    • Fix the issue that TiDB panics when executing the projection operator #24264
    • Fix the issue that statistics might cause queries to panic #24061
    • Fix the issue that using the approx_percentile function on a BIT column might panic #23662
    • Fix the issue that the metrics on the Coprocessor Cache panel in Grafana are wrong #26338
    • Fix the issue that concurrently truncating the same partition causes DDL statements to stuck #26229
    • Fix the issue of wrong query results that occurs when the session variable is used as the GROUP BY item #27106
    • Fix the wrong implicit conversion between VARCHAR and timestamp when joining tables #25902
    • Fix the wrong results in associated subquery statements #27233

  • TiKV

    • Fix the potential disk full issue caused by corrupted snapshot files #10813
    • Fix the TiKV panic issue that occurs when upgrading from a pre-5.0 version with Titan enabled #10843
    • Fix the issue that TiKV of a newer version cannot be rolled back to v5.0.x #10843
    • Fix the TiKV panic issue that occurs when upgrading from a pre-5.0 version to a 5.0 version or later. If a cluster was upgraded from TiKV v3.x with Titan enabled before the upgrade, this cluster might encounter the issue. #10774
    • Fix the parsing failure caused by the left pessimistic locks #26404
    • Fix the panic that occurs when calculating duration on certain platforms #10571
    • Fix the issue that the keys of batch_get_command in Load Base Split are unencoded #10542

  • 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 the scheduling conflict issue that occurs when multiple schedulers are running at same time #3807
    • Fix the issue that the scheduler might appear again even if it has been deleted #2572

  • TiFlash

    • Fix the potential panic issue that occurs when running table scan tasks
    • Fix the potential memory leak issue that occurs when executing MPP tasks
    • Fix a bug that TiFlash raises the duplicated region error when handling DAQ requests
    • Fix the issue of unexpected results when executing the aggregation functions COUNT or COUNT DISTINCT
    • Fix the potential panic issue that occurs when executing MPP tasks
    • Fix a potential bug that TiFlash cannot restore data when deployed on multiple disks
    • Fix the potential panic issue that occurs when deconstructing SharedQueryBlockInputStream
    • Fix the potential panic issue that occurs when deconstructing MPPTask
    • Fix the issue of unexpected results when TiFlash fails to establish MPP connections
    • Fix the potential panic issue that occurs when resolving locks
    • Fix the issue that the store size in metrics is inaccurate under heavy writing
    • Fix a bug of incorrect results that occurs when queries contain filters like CONSTANT, <, <=, >, >=, or COLUMN
    • Fix the potential issue that TiFlash cannot garbage-collect the delta data after running for a long time
    • Fix a potential bug that metrics display wrong values
    • Fix the potential issue of data inconsistency that occurs when TiFlash is deployed on multiple disks

  • Tools

    • Dumpling

      • Fix the issue that the execution of show table status is stuck in MySQL 8.0.3 or a later version #322

    • TiCDC

      • 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 a data inconsistency issue that occurs because multiple processors might write data to the same table when this table is being re-scheduled #2417
      • Decrease the gRPC window size to avoid the OOM that occurs when TiCDC captures too many Regions #2724
      • Fix the error that the gRPC connection is frequently broken when the memory pressure is high #2202
      • Fix a bug that causes TiCDC to panic on the unsigned TINYINT type #2648
      • Fix the issue that TiCDC Open Protocol outputs an empty value when inserting a transaction and deleting data of the same row in the upstream #2612
      • Fix a bug that DDL handling fails when a changefeed starts at the finish TS of a schema change #2603
      • Fix the issue that irresponsive downstreams interrupt the replication task in old owner until the task times out #2295
      • Fix a bug in metadata management #2558
      • Fix the issue of data inconsistency that occurs after the TiCDC owner switch #2230
      • Fix the issue that outdated capture might appear in the output of the capture list command #2388
      • Fix the ErrSchemaStorageTableMiss error that occurs when the DDL Job duplication is encountered in the integrated test #2422
      • Fix the bug that a changefeed cannot be removed if the ErrGCTTLExceeded error occurs #2391
      • Fix a bug that replicating large tables to cdclog fails #1259 #2424
      • Fix the CLI backward compatibility issue #2373
      • Fix the issue of insecure concurrent access to the map in SinkManager #2299
      • Fix the issue of potential DDL loss when the owner crashes when executing DDL statements #1260
      • Fix the issue that the lock is resolved immediately after a Region is initialized #2188
      • Fix the issue of extra partition dispatching that occurs when adding a new partitioned table #2263
      • Fix the issue that TiCDC keeps warning on removed changefeeds #2156