tasks, and the task records persist after the restart. When tidb_analyze_version = 2, the Job_info column adds the analyze option infor- mation. • Damaged SST files in TiKV might cause the TiKV process task type) #33332 • Support using rand() as the default value of a column #10377 • Support using uuid() as the default value of a column #33870 • Support modifying the character set of columns from latin1 caused by out-of-bounds data in the auto_increment column #29737 • Fix the issue of local backend import failure when the auto_random or auto_increment column is null #34208 85 2.3 TiDB Features This document

· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 6722 17.3.3 Column Family (CF) · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 6729 17.15.2 Static Sorted Table / Sorted String Table (SST) · · · · · · · · · · · · · · · · · · · 6730 17.15.3 Store limitations because it does not support global indexes. For example, the unique key must use every column in the table’s partition expression. If the query condition does not use the partition key, the query

@AilinKid • Fix the issue that executing ALTER TABLE ... LAST PARTITION fails when the partition column type is DATETIME #48814 @crazycs520 • Fix the issue that using the _ wildcard in LIKE when the data tidb_server_memory_limit #48741 @XuHuaiyu • Fix the issue that the query result is incorrect when an ENUM type column is used as the join key #48991 @winoros • Fix the issue that queries containing CTEs unexpectedly @mjonss • Fix the issue that the START_TIME column type in INFORMATION_SCHEMA. �→ CLUSTER_INFO is not valid #45221 @dveeden • Fix the issue that invalid EXTRA column type in INFORMATION_SCHEMA.COLUMNS �→

�→ _blank">Generated columns (GA) Values in a generated column are calculated by a SQL expression in the �→ column definition in real time. This feature pushes some application �→ logic 0/en/ldap-pluggable-authentication �→ .html" target="_blank">MySQL 8.0. Audit TiFlash first scans the column data related to the filter conditions that are pushed down to the TableScan operator, filters the rows that meet the condition, and then scans the other column data of these rows

threshold via tidb_server_memory_limit. • The high-performance and globally monotonic AUTO_INCREMENT column attribute be- comes GA, which is compatible with MySQL. • FLASHBACK CLUSTER TO TIMESTAMP is now optimizes the rewriting of COUNT(*) and automatically selects the not-null columns with the shortest column definition to count the number of rows, which can effectively 39 reduce the number of I/O operations 2.2.1.7 MySQL compatibility • Support a high-performance and globally monotonic AUTO_INCREMENT column attribute (GA) #38442 @tiancaiamao Since v6.4.0, TiDB has introduced the AUTO_INCREMENT MySQL compatibility

limitations because it does not support global indexes. For example, the unique key must use every column in the table’s partition expression. If the query condition does not use the partition key, the query address issues of Checksum V1 in verifying old values in Update or Delete events after ADD COLUMN or DROP COLUMN operations. For clusters created in v8.4.0 or later, or clusters upgraded to v8.4.0, TiDB index is en- abled by de- fault. You only need to add the key- word GLOBAL to the corre- spond- ing column when execut- ing CREATE �→ �→ TABLE �→ or ALTER �→ TABLE �→ to create a global index. 49 Variable

ALTER. This method is limited in some scenarios. For example, the application allows ADD COLUMN but not DROP COLUMN, but they are both filtered by ALTER events in the earlier DM versions. To address such the granularity of the supported DDL events, such as support filtering MODIFY COLUMN (modify the column data type), DROP COLUMN, and other fine-grained DDL events that lead to data loss, truncation of data parti- tions. v7.5.0 in- troduces a new value option columns, which uses the explic- itly specified column values to calculate the partition number. 53 Configuration file Configuration parame- ter Change

using more expressions to set default column values when creating a table (GA) #50936 @zimulala Before v8.0.0, when you create a table, the default value of a column is limited to strings, numbers, dates Starting from v8.0.0, you can use more expressions as the default column values. For example, you can set the default value of a column to DATE_FORMAT. This feature helps you meet more diverse require- becomes GA. Starting from v8.1.0, you can use expressions as default values when adding columns by ADD COLUMN. For more information, see documentation. 2.2.1.3 DB operations 41 • Enable the TiDB Distributed

all columns. To enable this feature, you need to manually set the system variable tidb_ �→ analyze_column_options to PREDICATE. For newly deployed clusters, this feature is enabled by default. For analytical analytical systems with many random queries, you can set the system variable tidb_analyze_column_options to ALL to collect statistics for all columns, to ensure the performance of random queries. For other other types of systems, it is recommended to keep the default setting (PREDICATE) of tidb_analyze_column_options to collect statistics for only necessary columns. For more information, see documentation.

the cluster size. 44 Variable name Change type Description tidb_ �→ analyze �→ _ �→ skip �→ _ �→ column �→ _ �→ types �→ Modified Starting from v8.2.0, TiDB does not collect columns of MEDIUMTEXT �→ and the performance is improved by 3 to 6 times #53246 @D3Hunter • Improve the logic of matching multi-column indexes using expressions like ((a �→ = 1 and b = 2 and c > 3)or (a = 4 and b = 5 and c > 6))and to 1048576 to avoid causing TiDB Server OOM when setting it too large #53312 @djshow832 • Improve column pruning for MPP execution plans to improve TiFlash MPP exe- cution performance #52133 @yibin87 •