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TiDB 6.4.0 Release Notes

Release date: November 17, 2022

TiDB version: 6.4.0-DMR

Quick access: Quick start

In v6.4.0-DMR, the key new features and improvements are as follows:

New features

SQL

  • Support using a SQL statement to compact TiFlash replicas of specified partitions in a table immediately #5315 @hehechen

    Since v6.2.0, TiDB has supported the feature of compacting physical data immediately on a full-table replica of TiFlash. You can choose the right time to manually execute SQL statements to immediately compact the physical data in TiFlash, which helps to reduce storage space and improve query performance. In v6.4.0, we refine the granularity of TiFlash replica data to be compacted and support compacting TiFlash replicas of specified partitions in a table immediately.

    By executing the SQL statement ALTER TABLE table_name COMPACT [PARTITION PartitionNameList] [engine_type REPLICA], you can immediately compact TiFlash replicas of specified partitions in a table.

    For more information, see User document.

  • Support restoring a cluster to a specific point in time by using FLASHBACK CLUSTER TO TIMESTAMP (experimental) #37197 #13303 @Defined2014 @bb7133 @JmPotato @Connor1996 @HuSharp @CalvinNeo

    You can use the FLASHBACK CLUSTER TO TIMESTAMP syntax to restore a cluster to a specific point in time quickly within the Garbage Collection (GC) lifetime. This feature helps you to easily and quickly undo DML misoperations. For example, you can use this syntax to restore the original cluster in minutes after mistakenly executing DELETE without a WHERE clause. This feature does not rely on database backups and supports rolling back data at different time points to determine the exact time when data changes. Note that FLASHBACK CLUSTER TO TIMESTAMP cannot replace database backups.

    Before executing FLASHBACK CLUSTER TO TIMESTAMP, you need to pause PITR and replication tasks running on such tools as TiCDC and restart them after the FLASHBACK is completed. Otherwise, replication tasks might fail.

    For more information, see User document.

  • Support restoring a deleted database by using FLASHBACK DATABASE #20463 @erwadba

    By using FLASHBACK DATABASE, you can restore a database and its data deleted by DROP within the garbage collection (GC) life time. This feature does not depend on any external tools. You can quickly restore data and metadata using SQL statements.

    For more information, see User document.

Security

  • TiFlash supports the SM4 algorithm for encryption at rest #5953 @lidezhu

    Add the SM4 algorithm for TiFlash encryption at rest. When you configure encryption at rest, you can enable the SM4 encryption capacity by setting the value of the data-encryption-method configuration to sm4-ctr in the tiflash-learner.toml configuration file.

    For more information, see User document.

Observability

  • Cluster diagnostics becomes GA #1438 @Hawkson-jee

    The cluster diagnostics feature in TiDB Dashboard diagnoses the problems that might exist in a cluster within a specified time range, and summarizes the diagnostic results and the cluster-related load monitoring information into a diagnostic report. This diagnostic report is in the form of a web page. You can browse the page offline and circulate this page link after saving the page from a browser.

    With the diagnostic reports, you can quickly understand the basic health information of the cluster, including the load, component status, time consumption, and configurations. If the cluster has some common problems, you can locate the causes in the result of the built-in automatic diagnosis in the diagnostic information section.

Performance

  • Introduce the concurrency adaptive mechanism for coprocessor tasks #37724 @you06

    As the number of coprocessor tasks increases, based on TiKV's processing speed, TiDB automatically increases concurrency (adjust the value of tidb_distsql_scan_concurrency) to reduce the coprocessor task queue and thus reduce latency.

  • Add the dynamic planning algorithm to determine table join order #37825 @winoros

    In earlier versions, TiDB uses the greedy algorithm to determine the join order of tables. In v6.4.0, the TiDB optimizer introduces the dynamic planning algorithm. The dynamic planning algorithm can enumerate more possible join orders than the greedy algorithm, so it increases the possibility to find a better execution plan and improves SQL execution efficiency in some scenarios.

    Because the dynamic programming algorithm consumes more time, the selection of the TiDB Join Reorder algorithms is controlled by the tidb_opt_join_reorder_threshold variable. If the number of nodes participating in Join Reorder is greater than this threshold, TiDB uses the greedy algorithm. Otherwise, TiDB uses the dynamic programming algorithm.

    For more information, see User document.

  • The prefix index supports filtering null values. #21145 @xuyifangreeneyes

    This feature is an optimization for the prefix index. When a column in a table has a prefix index, the IS NULL or IS NOT NULL condition of the column in the SQL statement can be directly filtered by the prefix, which avoids table lookup in this case and improves the performance of the SQL execution.

    For more information, see User document.

  • Enhance the TiDB chunk reuse mechanism #38606 @keeplearning20221

    In earlier versions, TiDB only reuses chunks in the writechunk function. TiDB v6.4.0 extends the chunk reuse mechanism to operators in Executor. By reusing chunks, TiDB does not need to frequently request memory release and SQL queries are executed more efficiently in some scenarios. You can use the system variable tidb_enable_reuse_chunk to control whether to reuse chunk objects, which is enabled by default.

    For more information, see User document.

  • Introduce a new optimizer hint NO_DECORRELATE to control whether to perform decorrelation for correlated subqueries #37789 @time-and-fate

    By default, TiDB always tries to rewrite correlated subqueries to perform decorrelation, which usually improves execution efficiency. However, in some scenarios, decorrelation reduces the execution efficiency. In v6.4.0, TiDB introduces the optimizer hint NO_DECORRELATE to tell the optimizer not to perform decorrelation for specified query blocks to improve query performance in some scenarios.

    For more information, see User document.

  • Improve the performance of statistics collection on partitioned tables #37977 @Yisaer

    In v6.4.0, TiDB optimizes the strategy of collecting statistics on partitioned tables. You can use the system variable tidb_auto_analyze_partition_batch_size to set the concurrency of collecting statistics on partitioned tables in parallel to speed up the collection and shorten the analysis time.

Stability

  • Accelerate fault recovery in extreme situations such as disk failures and stuck I/O #13648 @LykxSassinator

    For enterprise users, database availability is one of the most important metrics. While in complex hardware environments, how to quickly detect and recover from failures has always been one of the challenges of database availability. In v6.4.0, TiDB fully optimizes the state detection mechanism of TiKV nodes. Even in extreme situations such as disk failures and stuck I/O, TiDB can still report node state quickly and use the active wake-up mechanism to launch Leader election in advance, which accelerates cluster self-healing. Through this optimization, TiDB can shorten the cluster recovery time by about 50% in the case of disk failures.

  • Global control on TiDB memory usage #37816 @wshwsh12

    In v6.4.0, TiDB introduces global control of memory usage as an experimental feature that tracks the global memory usage of TiDB instances. You can use the system variable tidb_server_memory_limit to set the upper limit for the global memory usage. When the memory usage reaches the threshold, TiDB tries to reclaim and release more free memory. When the memory usage exceeds the threshold, TiDB identifies and cancels the SQL operation that has the highest memory usage to avoid system issues caused by excessive memory usage.

    When the memory consumption of TiDB instances has potential risks, TiDB will collect diagnostic information in advance and write it to the specified directory to facilitate the issue diagnosis. At the same time, TiDB provides system table views INFORMATION_SCHEMA.MEMORY_USAGE and INFORMATION_SCHEMA.MEMORY_USAGE_OPS_HISTORY that show the memory usage and operation history to help you better understand the memory usage.

    Global memory control is a milestone in TiDB memory management. It introduces a global view for instances and adopts systematic management for memory, which can greatly enhance database stability and service availability in more key scenarios.

    For more information, see User document.

  • Control the memory usage of the range-building optimizer #37176 @xuyifangreeneyes

    In v6.4.0, the system variable tidb_opt_range_max_size is introduced to limit the maximum memory usage of the optimizer that builds ranges. When the memory usage exceeds the limit, the optimizer will build more coarse-grained ranges instead of more exact ranges to reduce memory consumption. If a SQL statement has many IN conditions, this optimization can significantly reduce the memory usage of compiling and ensure system stability.

    For more information, see User document.

  • Support synchronously loading statistics (GA) #37434 @chrysan

    TiDB v6.4.0 enables the synchronously loading statistics feature by default. This feature allows TiDB to synchronously load large-sized statistics (such as histograms, TopN, and Count-Min Sketch statistics) into memory when you execute SQL statements, which improves the completeness of statistics for SQL optimization.

    For more information, see User document.

  • Reduce the impact of batch write requests on the response time of lightweight transactional writes #13313 @glorv

    The business logic of some systems requires periodic batch DML tasks, but processing these batch write tasks increases the latency of online transactions. In v6.3.0, TiKV optimizes the scheduling of read requests in hybrid workload scenarios, so you can enable the readpool.unified.auto-adjust-pool-size configuration item to have TiKV automatically adjust the size of the UnifyReadPool thread pool for all read requests. In v6.4.0, TiKV can dynamically identify and prioritize write requests as well, and control the maximum bytes that the Apply thread can write for one FSM (Finite-state Machine) in one round of poll, thus reducing the impact of batch write requests on the response time of transactional writes.

Ease of use

  • TiKV API V2 becomes generally available (GA) #11745 @pingyu

    Before v6.1.0, TiKV only provides basic Key Value read and write capability because it only stores the raw data passed in by the client. In addition, due to different coding methods and unscoped data ranges, TiDB, Transactional KV, and RawKV cannot be used at the same time in the same TiKV cluster; instead, multiple clusters are needed in this case, thus increasing machine and deployment costs.

    TiKV API V2 provides a new RawKV storage format and access interface, which delivers the following benefits:

    • Store data in MVCC with the change timestamp of the data recorded, based on which Change Data Capture (CDC) is implemented. This feature is experimental and is detailed in TiKV-CDC.
    • Data is scoped according to different usage and API V2 supports co-existence of TiDB, Transactional KV, and RawKV applications in a single cluster.
    • Reserve the Key Space field to support features such as multi-tenancy.

    To enable TiKV API V2, set api-version = 2 in the [storage] section of the TiKV configuration file.

    For more information, see User document.

  • Improve the accuracy of TiFlash data replication progress #4902 @hehechen

    In TiDB, the PROGRESS field of the INFORMATION_SCHEMA.TIFLASH_REPLICA table is used to indicate the progress of data replication from the corresponding tables in TiKV to the TiFlash replicas. In earlier TiDB versions, the PROCESS field only provides the progress of data replication during the creation of the TiFlash replicas. After a TiFlash replica is created, if new data is imported to a corresponding table in TiKV, this field will not be updated to show the replication progress from TiKV to TiFlash for the new data.

    In v6.4.0, TiDB improves the update mechanism of data replication progress for TiFlash replicas. After a TiFlash replica is created, if new data is imported to a corresponding table in TiKV, the PROGRESS value in the INFORMATION_SCHEMA.TIFLASH_REPLICA table will be updated to show the actual replication progress from TiKV to TiFlash for the new data. With this improvement, you can easily view the actual progress of TiFlash data replication.

    For more information, see User document.

MySQL compatibility

  • Be compatible with the Linear Hash partitioning syntax #38450 @mjonss

    In the earlier version, TiDB has supported the Hash, Range, and List partitioning. Starting from v6.4.0, TiDB can also be compatible with the syntaxt of MySQL Linear Hash partitioning.

    In TiDB, you can execute the existing DDL statements of your MySQL Linear Hash partitions directly, and TiDB will create the corresponding Hash partition tables (note that there is no Linear Hash partition inside TiDB). You can also execute the existing DML statements of your MySQL Linear Hash partitions directly, and TiDB will return the query result of the corresponding TiDB Hash partitions normally. This feature ensures the TiDB syntax compatibility with MySQL Linear Hash partitions and facilitates seamless migration from MySQL-based applications to TiDB.

    If the number of partitions is a power of 2, the rows in a TiDB Hash partitioned table are distributed the same as that in the MySQL Linear Hash partitioned table. Otherwise, the distribution of these rows in TiDB is different from MySQL.

    For more information, see User document.

  • Support a high-performance and globally monotonic AUTO_INCREMENT (experimental) #38442 @tiancaiamao

    TiDB v6.4.0 introduces the AUTO_INCREMENT MySQL compatibility mode. This mode introduces a centralized auto-increment ID allocating service that ensures IDs monotonically increase on all TiDB instances. This feature makes it easier to sort query results by auto-increment IDs. To use the MySQL compatibility mode, you need to set AUTO_ID_CACHE to 1 when creating a table. The following is an example:

    CREATE TABLE t (a INT AUTO_INCREMENT PRIMARY KEY) AUTO_ID_CACHE = 1;

    For more information, see User document.

  • Support range selection of array data in the JSON type #13644 @YangKeao

    Starting from v6.4.0, you can use the MySQL-compatible range selection syntax in TiDB.

    • With the keyword to, you can specify the start and end positions of array elements and select elements of a continuous range in an array. With 0, you can specify the position of the first element in an array. For example, using $[0 to 2], you can select the first three elements of an array.

    • With the keyword last, you can specify the position of the last element in an array, which allows you to set the position from right to left. For example, using $[last-2 to last], you can select the last three elements of an array.

      This feature simplifies the process of writing SQL statements, further improves the JSON type compatibility, and reduces the difficulty of migrating MySQL applications to TiDB.

  • Support adding additional descriptions for database users #38172 @CbcWestwolf

    In TiDB v6.4, you can use the CREATE USER or ALTER USER to add additional descriptions for database users. TiDB provides two description formats. You can add a text comment using COMMENT and add a set of structured attributes in JSON format using ATTRIBUTE.

    In addition, TiDB v6.4.0 adds the USER_ATTRIBUTES table, where you can view the information of user comments and user attributes.

    CREATE USER 'newuser1'@'%' COMMENT 'This user is created only for test'; CREATE USER 'newuser2'@'%' ATTRIBUTE '{"email": "user@pingcap.com"}'; SELECT * FROM INFORMATION_SCHEMA.USER_ATTRIBUTES;
    +-----------+------+---------------------------------------------------+ | USER | HOST | ATTRIBUTE | +-----------+------+---------------------------------------------------+ | newuser1 | % | {"comment": "This user is created only for test"} | | newuser1 | % | {"email": "user@pingcap.com"} | +-----------+------+---------------------------------------------------+ 2 rows in set (0.00 sec)

    This feature improves TiDB compatibility with MySQL syntax and makes it easier to integrate TiDB into tools or platforms in the MySQL ecosystem.

Backup and restore

  • Support backing up a TiDB cluster using EBS volume snapshots #33849 @fengou1

    If your TiDB cluster is deployed on EKS and uses AWS EBS volumes, and you have the following requirements when backing up TiDB cluster data, you can use TiDB Operator to back up the data by volume snapshots and metadata to AWS S3:

    • Minimize the impact of backup, for example, to keep the impact on QPS and transaction latency less than 5%, and to occupy no cluster CPU and memory.
    • Back up and restore data in a short time. For example, finish backup within 1 hour and restore data in 2 hours.

    For more information, see User document.

Data migration

  • DM supports writing upstream data source information to the extended columns of the downstream merged table #37797 @lichunzhu

    When merging sharded schemas and tables from upstream to TiDB, you can manually add several fields (extended columns) in the target table and specify their values when configuring the DM task. For example, if you specify the names of the upstream sharded schema and table for the extended columns, the data written to the downstream by DM will include the schema name and table name. When the downstream data looks unusual, you can use this feature to quickly locate the data source information in the target table, such as the schema name and table name.

    For more information, see Extract table, schema, and source information and write into the merged table.

  • DM optimizes the pre-check mechanism by changing some mandatory check items to optional ones #7333 @lichunzhu

    To run a data migration task smoothly, DM triggers a precheck automatically at the start of the task and returns the check results. DM starts the migration only after the precheck is passed.

    In v6.4.0, DM changes the following three check items from mandatory to optional, which improves the pass rate of the pre-check:

    • Check whether the upstream tables use character sets that are incompatible with TiDB.
    • Check whether the upstream tables have primary key constraints or unique key constraints
    • Check whether the database ID server_id for the upstream database has been specified in the primary-secondary configuration.
  • DM supports configuring binlog position and GTID as optional parameters for incremental migration tasks #7393 @GMHDBJD

    Since v6.4.0, you can perform incremental migration directly without specifying the binlog position or GTID. DM automatically obtains the binlog files generated after the task starts from upstream and migrates these incremental data to the downstream. This relieves users from laborious understanding and complicated configuration.

    For more information, see DM Advanced Task Configuration File.

  • DM adds more status indicators for migration tasks #7343 @okJiang

    In v6.4.0, DM adds more performance and progress indicators for migration tasks, which helps you understand the migration performance and progress more intuitively and provides you with a reference for troubleshooting.

    • Add status indicators (in bytes/s) showing data importing and exporting performance.

    • Rename the performance indicator for writing data to the downstream database from TPS to RPS (in rows/s).

    • Add progress indicators showing the data export progress of DM full migration tasks.

      For more information about these indicators, see Query Task Status in TiDB Data Migration.

TiDB data share subscription

Compatibility changes

System variables

Variable nameChange typeDescription
tidb_constraint_check_in_place_pessimisticModifiedRemoves the GLOBAL scope and allows you to modify the default value using the pessimistic-txn.constraint-check-in-place-pessimistic configuration item. This variable controls when TiDB checks the unique constraints in pessimistic transactions.
tidb_ddl_flashback_concurrencyModifiedTakes effect starting from v6.4.0 and controls the concurrency of FLASHBACK CLUSTER TO TIMESTAMP. The default value is 64.
tidb_enable_clustered_indexModifiedChanges the default value from INT_ONLY to ON, meaning that primary keys are created as clustered indexes by default.
tidb_enable_pagingModifiedChanges the default value from OFF to ON, meaning that the method of paging to send coprocessor requests is used by default.
tidb_enable_prepared_plan_cacheModifiedAdds the SESSION scope. This variable controls whether to enable Prepared Plan Cache.
tidb_memory_usage_alarm_ratioModifiedChanges the default value from 0.8 to 0.7. This variable controls the memory usage ratio that triggers the tidb-server memory alarm.
tidb_opt_agg_push_downModifiedAdds the GLOBAL scope. This variable controls whether the optimizer executes the optimization operation of pushing down the aggregate function to the position before Join, Projection, and UnionAll.
tidb_prepared_plan_cache_sizeModifiedAdds the SESSION scope. This variable controls the maximum number of plans that can be cached in a session.
tidb_stats_load_sync_waitModifiedChanges the default value from 0 to 100, meaning that the SQL execution can wait for at most 100 milliseconds by default to synchronously load complete column statistics.
tidb_stats_load_pseudo_timeoutModifiedChanges the default value from OFF to ON, meaning that the SQL optimization gets back to using pseudo statistics after reaching the timeout of synchronously loading complete column statistics.
last_sql_use_allocNewly addedShows whether the previous statement uses a cached chunk object (chunk allocation). This variable is read-only and the default value is OFF.
tidb_auto_analyze_partition_batch_sizeNewly addedSpecifies the number of partitions that TiDB can automatically analyzes at a time when analyzing a partitioned table (which means automatically collecting statistics on a partitioned table). The default value is 1.
tidb_enable_external_ts_readNewly addedControls whether TiDB reads data with the timestamp specified by tidb_external_ts. The default value is OFF.
tidb_enable_gogc_tunerNewly addedControls whether to enable GOGC Tuner. The default value is ON.
tidb_enable_reuse_chunkNewly addedControls whether TiDB enables chunk objects cache. The default value is ON, meaning that TiDB prefers to use the cached chunk object and only requests from the system if the requested object is not in the cache. If the value is OFF, TiDB requests chunk objects from the system directly.
tidb_enable_prepared_plan_cache_memory_monitorNewly addedControls whether to count the memory consumed by the execution plans cached in the Prepared Plan Cache. The default value is ON.
tidb_external_tsNewly addedThe default value is 0. If tidb_enable_external_ts_read is set to ON, TiDB reads data with the timestamp specified by this variable.
tidb_gogc_tuner_thresholdNewly addedSpecifies the maximum memory threshold for tuning GOGC. When the memory exceeds this threshold, GOGC Tuner stops working. The default value is 0.6.
tidb_memory_usage_alarm_keep_record_numNewly addedWhen the tidb-server memory usage exceeds the memory alarm threshold and triggers an alarm, TiDB only retains the status files generated during the recent 5 alarms by default. You can adjust this number with this variable.
tidb_opt_prefix_index_single_scanNewly addedControls whether the TiDB optimizer pushes down some filter conditions to the prefix index to avoid unnecessary table lookup and to improve query performance. The default value is ON.
tidb_opt_range_max_sizeNewly addedSpecifies the upper limit of memory usage for the optimizer to construct a scan range. The default value is 67108864 (64 MiB).
tidb_server_memory_limitNewly addedControls the upper limit of memory usage for the optimizer to build scan ranges (experimental). The default value is 0, meaning that there is no memory limit.
tidb_server_memory_limit_gc_triggerNewly addedControls the threshold at which TiDB tries to trigger GC (experimental). The default value is 70%.
tidb_server_memory_limit_sess_min_sizeNewly addedAfter you enable the memory limit, TiDB will terminate the SQL statement with the highest memory usage on the current instance. This variable specifies the minimum memory usage of the SQL statement to be terminated. The default value is 134217728 (128 MiB).

Configuration file parameters

Configuration fileConfiguration parameterChange typeDescription
TiDBtidb_memory_usage_alarm_ratioDeletedThis configuration item is no longer effective.
TiDBmemory-usage-alarm-ratioDeletedReplaced by the system variable tidb_memory_usage_alarm_ratio. If this configuration item has been configured in a TiDB version earlier than v6.4.0, it will not take effect after the upgrade.
TiDBpessimistic-txn.constraint-check-in-place-pessimisticNewly addedControls the default value of the system variable tidb_constraint_check_in_place_pessimistic. The default value is true.
TiDBtidb-max-reuse-chunkNewly addedControls the maximum cached chunk objects of chunk allocation. The default value is 64.
TiDBtidb-max-reuse-columnNewly addedControls the maximum cached column objects of chunk allocation. The default value is 256.
TiKVcdc.raw-min-ts-outlier-thresholdDeprecatedThis configuration item is no longer effective.
TiKVcausal-ts.alloc-ahead-bufferNewly addedThe pre-allocated TSO cache size (in duration). The default value is 3s.
TiKVcausal-ts.renew-batch-max-sizeNewly addedControls the maximum number of TSOs in a timestamp request. The default value is 8192.
TiKVraftstore.apply-yield-write-sizeNewly addedControls the maximum number of bytes that the Apply thread can write for one FSM (Finite-state Machine) in one round of poll. The default value is 32KiB. This is a soft limit.
PDtso-update-physical-intervalNewly addedTakes effect starting from v6.4.0 and controls the interval at which PD updates the physical time of TSO. The default value is 50ms.
TiFlashdata-encryption-methodModifiedIntroduces a new value option sm4-ctr. When this configuration item is set to sm4-ctr, data is encrypted using SM4 before being stored.
DMroutes.route-rule-1.extract-tableNewly addedOptional. Used in the sharding scenario for extracting the source information of sharded tables. The extracted information will be written to the merged table in the downstream to identify the data source. If this parameter is configured, you need to manually create a merged table in the downstream in advance.
DMroutes.route-rule-1.extract-schemaNewly addedOptional. Used in the sharding scenario for extracting the source information of sharded schemas. The extracted information will be written to the merged table in the downstream to identify the data source. If this parameter is configured, you need to manually create a merged table in the downstream in advance.
DMroutes.route-rule-1.extract-sourceNewly addedOptional. Used in the sharding scenario for extracting the source instance information. The extracted information will be written to the merged table in the downstream to identify the data source. If this parameter is configured, you need to manually create a merged table in the downstream in advance.
TiCDCtransaction-atomicityModifiedChanges the default value from table to none. This change helps reduce replication latency and OOM risks. In addition, TiCDC now only splits a few transactions (the size of a single transaction exceeds 1024 rows), instead of all transactions.

Others

  • Starting from v6.4.0, the mysql.user table adds two new columns: User_attributes and Token_issuer. If you restore system tables in the mysql schema from backup data of earlier TiDB versions to TiDB v6.4.0, BR will report the column count mismatch error for the mysql.user table. If you do not restore system tables in the mysql schema, this error will not be reported.
  • For files whose names match the format of Dumpling exported files but end with uncompressed formats (such as test-schema-create.sql.origin and test.table-schema.sql.origin), the way how TiDB Lightning handles them is changed. Before v6.4.0, if the files to be imported include such files, TiDB Lightning skips importing such files. Starting from v6.4.0, TiDB Lightning assumes that such files use unsupported compression formats, so the import task will fail.
  • Starting with v6.4.0, only the changefeed with the SYSTEM_VARIABLES_ADMIN or SUPER privilege can use the TiCDC Syncpoint feature.

Improvements

  • TiDB

    • Allow modifying the noop variable lc_messages #38231 @djshow832
    • Support the AUTO_RANDOM column as the first column of the clustered composite index #38572 @tangenta
    • Use pessimistic transactions in internal transaction retry to avoid retry failure and reduce time consumption #38136 @jackysp
  • TiKV

    • Add a new configuration item apply-yield-write-size to control the maximum number of bytes that the Apply thread can write for one Finite-state Machine in one round of poll, and relieve Raftstore congestion when the Apply thread writes a large volume of data #13313 @glorv
    • Warm up the entry cache before migrating the leader of Region to avoid QPS jitter during the leader transfer process #13060 @cosven
    • Support pushing down the json_constains operator to Coprocessor #13592 @lizhenhuan
    • Add the asynchronous function for CausalTsProvider to improve the flush performance in some scenarios #13428 @zeminzhou
  • PD

    • The v2 algorithm of the hot Region scheduler becomes GA. In some scenarios, the v2 algorithm can achieve better balancing in both configured dimensions and reduce invalid scheduling #5021 @HundunDM
    • Optimize the timeout mechanism of operator step to avoid premature timeout #5596 @bufferflies
    • Improve the performance of the scheduler in large clusters #5473 @bufferflies
    • Support using external timestamp which is not provided by PD #5637 @lhy1024
  • TiFlash

    • Refactor the TiFlash MPP error handling logic to further improve the stability of MPP #5095 @windtalker
    • Optimize the sorting of the TiFlash computation process, and optimize the key handling for Join and Aggregation #5294 @solotzg
    • Optimize the memory usage for decoding and remove redundant transfer columns to improve Join performance #6157 @yibin87
  • Tools

    • TiDB Dashboard

      • Support displaying TiFlash metrics on the Monitoring page and optimize the presentation of metrics on that page #1440 @YiniXu9506
      • Show the number of rows for results in the Slow Query list and SQL Statement list #1443 @baurine
      • Optimize the Dashboard to not report the Alertmanager errors when Alertmanager does not exist #1444 @baurine
    • Backup & Restore (BR)

      • Improve the mechanism for loading the metadata. The metadata is loaded into memory only when necessary, which significantly reduces the memory usage during PITR #38404 @YuJuncen
    • TiCDC

      • Support replicating the exchange partition DDL statements #639 @asddongmen
      • Improve non-batch sending performance for the MQ sink module #7353 @hi-rustin
      • Improve performance of TiCDC puller when a table has a large number of Regions #7078 #7281 @sdojjy
      • Support reading historical data in the downstream TiDB by using the tidb_enable_external_ts_read variable when Syncpoint is enabled #7419 @asddongmen
      • Enable transaction split and disable safeMode by default to improve the replication stability #7505 @asddongmen
    • TiDB Data Migration (DM)

      • Remove the useless operate-source update command from dmctl #7246 @buchuitoudegou
      • Fix the issue that DM full import fails if the upstream database uses DDL statements that are incompatible with TiDB. You can create the schema of target tables in TiDB manually in advance using DDL statements supported by TiDB to ensure successful import #37984 @lance6716
    • TiDB Lightning

      • Optimize the file scanning logic to accelerate the scan of schema files #38598 @dsdashun

Bug fixes

  • TiDB

    • Fix the potential issue of index inconsistency that occurs after you create a new index #38165 @tangenta
    • Fix a permission issue of the INFORMATION_SCHEMA.TIKV_REGION_STATUS table #38407 @CbcWestwolf
    • Fix the issue that the grantor field is missing in the mysql.tables_priv table #38293 @CbcWestwolf
    • Fix the issue that the join result of common table expressions might be wrong #38170 @wjhuang2016
    • Fix the issue that the union result of common table expressions might be wrong #37928 @YangKeao
    • Fix the issue that the information in the transaction region num monitoring panel is incorrect #38139 @jackysp
    • Fix the issue that the system variable tidb_constraint_check_in_place_pessimistic might affect internal transactions. The variable scope is modified to SESSION. #38766 @ekexium
    • Fix the issue that conditions in a query are mistakenly pushed down to projections #35623 @Reminiscent
    • Fix the issue that the wrong isNullRejected check results for AND and OR cause wrong query results #38304 @Yisaer
    • Fix the issue that ORDER BY in GROUP_CONCAT is not considered when the outer join is eliminated, which causes wrong query results #18216 @winoros
    • Fix the issue of the wrong query result that occurs when the mistakenly pushed-down conditions are discarded by Join Reorder #38736 @winoros
  • TiKV

    • Fix the issue that TiDB fails to start on Gitpod when there are multiple cgroup and mountinfo records #13660 @tabokie
    • Fix the wrong expression of a TiKV metric tikv_gc_compaction_filtered #13537 @Defined2014
    • Fix the performance issue caused by the abnormal delete_files_in_range #13534 @tabokie
    • Fix abnormal Region competition caused by expired lease during snapshot acquisition #13553 @SpadeA-Tang
    • Fix errors occurred when FLASHBACK fails in the first batch #13672 #13704 #13723 @HuSharp
  • PD

    • Fix inaccurate Stream timeout and accelerate leader switchover #5207 @CabinfeverB
  • TiFlash

    • Fix the OOM issue due to oversized WAL files that occurs when PageStorage GC does not clear the Page deletion marker properly #6163 @JaySon-Huang
  • Tools

    • TiDB Dashboard

      • Fix the TiDB OOM issue when querying execution plans of certain complex SQL statements #1386 @baurine
      • Fix the issue that the Top SQL switch might not take effect when NgMonitoring loses the connection to the PD nodes #164 @zhongzc
    • Backup & Restore (BR)

      • Fix the restoration failure issue caused by PD leader switch during the restoration process #36910 @MoCuishle28
      • Fix the issue that the log backup task cannot be paused #38250 @joccau
      • Fix the issue that when BR deletes log backup data, it mistakenly deletes data that should not be deleted #38939 @Leavrth
      • Fix the issue that BR fails to delete data when deleting the log backup data stored in Azure Blob Storage or Google Cloud Storage for the first time #38229 @Leavrth
    • TiCDC

      • Fix the issue that sasl-password in the changefeed query result is not masked #7182 @dveeden
      • Fix the issue that TiCDC might become unavailable when too many operations in an etcd transaction are committed #7131 @asddongmen
      • Fix the issue that redo logs might be deleted incorrectly #6413 @asddongmen
      • Fix performance regression when replicating wide tables in Kafka Sink V2 #7344 @hi-rustin
      • Fix the issue that checkpoint ts might be advanced incorrectly #7274 @hi-rustin
      • Fix the issue that too many logs are printed due to improper log level of the mounter module #7235 @hi-rustin
      • Fix the issue that a TiCDC cluster might have two owners #4051 @asddongmen
    • TiDB Data Migration (DM)

      • Fix the issue that DM WebUI generates the wrong allow-list parameter #7096 @zoubingwu
      • Fix the issue that a DM-worker has a certain probability of triggering data race when it starts or stops #6401 @liumengya94
      • Fix the issue that when DM replicates an UPDATE or DELETE statement but the corresponding row data does not exist, DM silently ignores the event #6383 @GMHDBJD
      • Fix the issue that the secondsBehindMaster field is not displayed after you run the query-status command #7189 @GMHDBJD
      • Fix the issue that updating the checkpoint may trigger a large transaction #5010 @lance6716
      • Fix the issue that in full task mode, when a task enters the sync stage and fails immediately, DM may lose upstream table schema information #7159 @lance6716
      • Fix the issue that deadlock may be triggered when the consistency check is enabled #7241 @buchuitoudegou
      • Fix the issue that task precheck requires the SELECT privilege for the INFORMATION_SCHEMA table #7317 @lance6716
      • Fix the issue that an empty TLS configuration causes an error #7384 @liumengya94
    • TiDB Lightning

      • Fix the import performance degradation when importing the Apache Parquet files to the target tables that contain the string type columns in thebinary encoding format #38351 @dsdashun
    • TiDB Dumpling

      • Fix the issue that Dumpling might time out when exporting a lot of tables #36549 @lance6716
      • Fix lock errors reported when consistency lock is enabled but the upstream has no target table #38683 @lance6716

Contributors

We would like to thank the following contributors from the TiDB community:

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