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TiDB 4.0 RC.2 Release Notes
/docs/dev/releases/release-4.0.0-rc.2/
TiDB 4.0 RC.2 was released on May 15, 2020. The release includes compatibility changes, important bug fixes, new features, and bug fixes for TiDB, TiKV, PD, TiFlash, and various tools. Some notable changes include the removal of the size limit for a single transaction when TiDB Binlog is enabled, support for the BACKUP and RESTORE commands, and the addition of encryption-related monitoring metrics in Grafana dashboard. Additionally, there are numerous bug fixes for issues such as wrong partition selection, incorrect index range building, and performance reduction. The release also introduces new features like support for the auto_random option in the CREATE TABLE statement and the ability to manage replication tasks using cdc cli.

TiDB 4.0 RC.2 Release Notes

Release date: May 15, 2020

TiDB version: 4.0.0-rc.2

Compatibility Changes

  • TiDB

    • Remove the size limit for a single transaction (100 MB) when TiDB Binlog is enabled. Now the size limit for a transaction is 10 GB. However, if TiDB Binlog is enabled and the downstream is Kafka, configure the txn-total-size-limit parameter according to the message size limit of 1 GB in Kafka #16941
    • Change the behavior from querying the default time range to returning an error and requesting a specified time range if the time range is not specified when querying the CLUSTER_LOG table #17003
    • If the unsupported sub-partition or linear hash option is specified when creating the partitioned table using the CREATE TABLE statement, the normal table is created rather than the partitioned table with the options ignored #17197

  • TiKV

    • Move the encryption-related configuration to the security-related configuration, which means changing [encryption] in the TiKV configuration file to [security.encryption] #7810

  • Tools

    • TiDB Lightning

      • Change the default SQL mode to ONLY_FULL_GROUP_BY,NO_AUTO_CREATE_USER when importing data to improve compatibility #316
      • Disallow accessing the PD or TiKV port in the tidb-backend mode #312
      • Print the log information to the tmp file by default, and print the path of the tmp file when TiDB Lightning is started #313

Important Bug Fixes

  • TiDB

    • Fix the issue that the wrong partition is chosen when the WHERE clause has only one equivalent condition #17054
    • Fix the issue of wrong results caused by building the incorrect Index range when the WHERE clause only contains the string column #16660
    • Fix the panic issue that occurs when executing the PointGet query in the transaction after the DELETE operation #16991
    • Fix the issue that the GC worker might encounter the deadlock when an error occurs #16915
    • Avoid the unnecessary RegionMiss retry when the TiKV response is slow but not down #16956
    • Change the log level in the client in the handshake phase of the MySQL protocol to DEBUG to solve the problem that interferes with log output #16881
    • Fix the issue that the Region is not pre-split according to the PRE_SPLIT_REGIONS information defined by the table after the TRUNCATE operation #16776
    • Fix the issue of soaring goroutine caused by retry when TiKV is unavailable during the second phase of the two-phase commit #16876
    • Fix the panic issue of statement execution when some expressions cannot be pushed down #16869
    • Fix the wrong execution result of the IndexMerge operation on the partitioned table #17124
    • Fix the performance reduction of wide_table caused by the mutex contention of Memory Trackers #17234

  • TiFlash

    • Fix the issue that the system cannot start normally after the upgrade if the name of the database or table contains special characters

New Features

  • TiDB

    • Add support for the BACKUP and RESTORE commands to back up and restore data #16960
    • Support pre-checking the data volume in a single Region before commit and pre-splitting the Region when the data volume exceeds the threshold #16959
    • Add the new LAST_PLAN_FROM_CACHE variable with a Session scope to indicate whether the last executed statement hits the plan cache #16830
    • Support recording the Cop_time information in slow log and the SLOW_LOG table #16904
    • Add in Grafana more metrics that monitor the memory status of Go Runtime #16928
    • Support outputting the forUpdateTS and Read Consistency isolation level information in General Log #16946
    • Support collapsing duplicate requests of resolving locks in TiKV Region #16925
    • Support using the SET CONFIG statement to modify the configuration of PD/TiKV nodes #16853
    • Support the auto_random option in the CREATE TABLE statement #16813
    • Allocate TaskID for the DistSQL request to help TiKV better schedule and process requests #17155
    • Support displaying the version information of the TiDB server after logging into the MySQL client #17187
    • Support the ORDER BY clause in the GROUP_CONCAT function #16990
    • Support displaying the Plan_from_cache information in slow log to indicate whether the statement hits plan cache #17121
    • Add the feature that TiDB Dashboard can display the capacity information of TiFlash multi-disk deployment
    • Add the feature of querying the TiFlash log using SQL statements in Dashboard

  • TiKV

    • Support encryption debugging for tikv-ctl, so that tikv-ctl can be used to operate and manage the cluster when the encryption storage is enabled #7698
    • Support encrypting the lock column family in snapshots #7712
    • Use the heatmap in the Grafana dashboard for Raftstore latency summary to better diagnose the jitter issue #7717
    • Support setting the upper limit for the size of the gRPC message #7824
    • Add in Grafana dashboard the encryption-related monitoring metrics #7827
    • Support Application-Layer Protocol Negotiation (ALPN) #7825
    • Add more statistics about Titan #7818
    • Support using the task ID provided by the client as the identifier in the unified read pool to avoid that the priority of a task is lowered by another task in the same transaction #7814
    • Improve the performance of the batch insert request #7718

  • PD

    • Eliminate the speed limit of removing peers when making a node offline #2372

  • TiFlash

    • Change the name of the Count graph of Read Index in Grafana to Ops
    • Optimize the data for opening file descriptors when the system load is low to reduce system resource consumption
    • Add the capacity-related configuration parameter to limit the data storage capacity

  • Tools

    • TiDB Lightning

      • Add the fetch-mode sub-command in tidb-lightning-ctl to print the TiKV cluster mode #287

    • TiCDC

      • Support managing the replication task by using cdc cli (changefeed) #546

    • Backup & Restore (BR)

      • Support automatically adjusting GC time during backup #257
      • Adjust PD parameters when restoring data to speed up the restoration #198

Bug Fixes

  • TiDB

    • Improve the logic that determines whether to use vectorization for expression execution in multiple operators #16383
    • Fix the issue that the IndexMerge hint fails to check the database name correctly #16932
    • Forbid truncating the sequence object #17037
    • Fix the issue that the INSERT/UPDATE/ANALYZE/DELETE statements can be performed on a sequence object #16957
    • Fix the issue that the internal SQL statements in the bootstrap phase are not correctly marked as internal queries in the Statement Summary table #17062
    • Fix the error that occurs when a filter condition supported by TiFlash but not by TiKV is pushed down to the IndexLookupJoin operator #17036
    • Fix the concurrency issue of the LIKE expression that might occur after the collation is enabled #16997
    • Fix the issue that the LIKE function cannot correctly build the Range query index after the collation is enabled #16783
    • Fix the issue that a wrong value is returned when executing @@LAST_PLAN_FROM_CACHE after the Plan Cache statement is triggered #16831
    • Fix the issue that TableFilter on the index is missed when calculating candidate paths for IndexMerge #16947
    • Fix the issue that a physical query plan cannot be generated when using the MergeJoin hint and the TableDual operator exists #17016
    • Fix the wrong capitalization of the values in the Stmt_Type column of the Statement Summary table #17018
    • Fix the issue that the Permission Denied error is reported because the service cannot be started when different users use the same tmp-storage-path #16996
    • Fix the issue that the NotNullFlag result type is incorrectly set for an expression whose result type is determined by multiple input columns, such as CASE WHEN #16995
    • Fix the issue that the green GC might leave unresolved locks when dirty stores exist #16949
    • Fix the issue that the green GC might leave unresolved locks when encountering a single key with multiple different locks #16948
    • Fix the issue of inserting a wrong value in the INSERT VALUE statement because a sub-query refers to a parent query column #16952
    • Fix the issue of incorrect results when using the AND operator on the Float value #16666
    • Fix the wrong information of the WAIT_TIME field in the expensive log #16907
    • Fix the issue that the SELECT FOR UPDATE statement cannot be recorded in the slow log in the pessimistic transaction mode #16897
    • Fix the wrong result that occurs when executing SELECT DISTINCT on a column of the Enum or Set type #16892
    • Fix the display error of auto_random_base in the SHOW CREATE TABLE statement #16864
    • Fix the incorrect value of string_value in the WHERE clause #16559
    • Fix the issue that the error message of the GROUP BY window function is inconsistent with that of MySQL #16165
    • Fix the issue that the FLASH TABLE statement fails to execute when the database name contains the uppercase letter #17167
    • Fix the inaccurate memory tracing of the Projection executor #17118
    • Fix the issue of incorrect time filtering of the SLOW_QUERY table in different time zones #17164
    • Fix the panic issue that occurs when IndexMerge is used with the virtual generated column #17126
    • Fix the capitalization issue of the INSTR and LOCATE function #17068
    • Fix the issue that the tikv server timeout error is reported frequently after the tidb_allow_batch_cop configuration is enabled #17161
    • Fix the issue that the result of performing XOR operation on the Float type is inconsistent with that of MySQL 8.0 #16978
    • Fix the issue that no error is reported when the unsupported ALTER TABLE REORGANIZE PARTITION statement is executed #17178
    • Fix the issue that an error is reported when EXPLAIN FORMAT="dot" FOR CONNECTION ID encounters an unsupported plan #17160
    • Fix the record issue of the prepared statement in the EXEC_COUNT column of the Statement Summary table #17086
    • Fix the issue that the value is not validated when setting the Statement Summary system variable #17129
    • Fix the issue that an error is reported if an overflow value is used to query the UNSIGNED BIGINT primary key when the plan cache is enabled #17120
    • Fix the incorrect QPS display by the machine instance and request type on the Grafana TiDB Summary dashboard #17105

  • TiKV

    • Fix the issue that many empty Regions are generated after restoration #7632
    • Fix the panic issue of Raftstore when receiving out-of-order read index responses #7370
    • Fix the issue that an invalid storage or coprocessor read pool configuration might not be rejected when the unified thread pool is enabled #7513
    • Fix the panic issue of the join operation when the TiKV server is shut down #7713
    • Fix the issue that no result is returned when searching TiKV slow logs via diagnostics API #7776
    • Fix the issue that notable memory fragmentation is generated when the TiKV node is running for a long time #7556
    • Fix the issue that the SQL statement fails to execute when an invalid date is stored #7268
    • Fix the issue that the backup data cannot be restored from GCS #7739
    • Fix the issue that KMS key ID is not validated during encryption at rest #7719
    • Fix the underlying correctness issue of the Coprocessor in compilers of different architecture #7714 #7730
    • Fix the snapshot ingestion error when encryption is enabled #7815
    • Fix the Invalid cross-device link error when rewriting the configuration file #7817
    • Fix the issue of wrong toml format when writing the configuration file to an empty file #7817
    • Fix the issue that a destroyed peer in Raftstore can still process requests #7836

  • PD

    • Fix the 404 issue that occurs when using the region key command in pd-ctl #2399
    • Fix the issue that the monitor metrics of TSO and ID allocation are missing from the Grafana dashboard #2405
    • Fix the issue that pd-recover is not included in the Docker image #2406
    • Parse the path of data directory to an absolute path to fix the issue that TiDB Dashboard might not correctly display PD information #2420
    • Fix the issue that there is no default output when using the scheduler config shuffle-region-scheduler command in pd-ctl #2416

  • TiFlash

    • Fix the issue that the wrong information of used capacity is report in some scenarios

  • Tools

    • TiDB Binlog

      • Fix the issue that data of the mediumint type is not processed when the downstream is Kafka #962
      • Fix the issue that the reparo fails to parse the DDL statement when the database name in DDL is a keyword #961

    • TiCDC

      • Fix the issue of using the wrong time zone when the TZ environment variable is not set #512
      • Fix the issue that the owner does not clean up the resources when the server exits because some errors are not handled correctly #528
      • Fix the issue that TiCDC might be stuck when reconnecting to TiKV #531
      • Optimize the memory usage when initializing the table schema #534
      • Use the watch mode to monitor the replication status changes and perform quasi-real-time updates to reduce replication delay #481

    • Backup & Restore (BR)

      • Fix the issue that inserting data might trigger the duplicate entry error after BR restores a table with the auto_random attribute #241