expression indexes to greatly improve query perfor- mance • Improve the accuracy of optimizer cardinality estimation to help to select optimal execution plans • Announce the general availability (GA) for the stress. User document, #25882 • Improve the accuracy of optimizer cardinality estimation – Improve the accuracy of TiDB’s estimation of TopN/Limit. For example, for pagination queries on a large table select the right index and reduce query response time. 36 – Improve the accuracy of out-of-range estimation. For example, even if the statis- tics for a day have not been updated, TiDB can accurately select

the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze ex- clude unsuitable indexes, and then selects the index with the lowest cost based on the cost estimation of each operator that accesses tables. Rule-based selection Pre-rules TiDB uses the following filtering rule for indexes, which can reduce the probability of wrong index selection caused by wrong estimation. To judge an index, the following three dimensions are needed: • How many access conditions are

TiDB server. tidb_enforce_mpp �→ Newly added Controls whether to ignore the optimizer’s cost estimation and to forcibly use the MPP mode for query execution. The data type of this variable is BOOL and that might occur in the large data volume caused by hash conflicts in Version 1 and maintains the estimation accuracy in most scenarios. User document 2.2.2.2 Transaction • Support the Lock View feature skyline-pruning based on the cost estimation of each operator for accessing tables. It can reduce the probability of wrong index selection caused by wrong estimation. Skyline-pruning Skyline-pruning

the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze ex- clude unsuitable indexes, and then selects the index with the lowest cost based on the cost estimation of each operator that accesses tables. Rule-based selection Pre-rules TiDB uses the following filtering rule for indexes, which can reduce the probability of wrong index selection caused by wrong estimation. To judge an index, the following three dimensions are needed: • How many access conditions are

the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze --------+ �→ | Table | Non_unique | Key_name | Seq_in_index | Column_name | �→ Collation | Cardinality | Sub_part | Packed | Null | Index_type | �→ Comment | Index_comment | Visible | Expression | Clustered ex- clude unsuitable indexes, and then selects the index with the lowest cost based on the cost estimation of each operator that accesses tables. Rule-based selection Pre-rules TiDB uses the following

introduces the Cost Model Version 2 as an experimental feature. This model uses a more accurate cost estimation method to help the optimizer choose the optimal execution plan. Especially when TiFlash is deployed the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze ---+ �→ 366 | Table | Non_unique | Key_name | Seq_in_index | Column_name | �→ Collation | Cardinality | Sub_part | Packed | Null | Index_type | �→ Comment | Index_comment | Visible | Expression | Clustered

issue of batch-client in client-go #47691 @crazycs520 • Fix the issue of incorrect memory usage estimation in INDEX_LOOKUP_HASH_JOIN #47788 @SeaRise • Fix the issue of uneven workload caused by the rejoining the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze ---+ �→ 347 | Table | Non_unique | Key_name | Seq_in_index | Column_name | �→ Collation | Cardinality | Sub_part | Packed | Null | Index_type | �→ Comment | Index_comment | Visible | Expression | Clustered

the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze --------+ �→ | Table | Non_unique | Key_name | Seq_in_index | Column_name | �→ Collation | Cardinality | Sub_part | Packed | Null | Index_type | �→ Comment | Index_comment | Visible | Expression | Clustered value does not represent the exact value for each execution, but can be used as a reference for estimation. 8.5.7.1.3 Slow queries and the corresponding system table When you enable resource control,

introduces the ability to estimate system capacity based on actual workload or hardware deployment. The estimation ability provides you with a more accurate reference for capacity planning and assists you in better the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze ---+ �→ 367 | Table | Non_unique | Key_name | Seq_in_index | Column_name | �→ Collation | Cardinality | Sub_part | Packed | Null | Index_type | �→ Comment | Index_comment | Visible | Expression | Clustered

issue that the optimizer does not use the best multi-column statistics information for row count estimation when the query contains filter conditions like (... AND ...)OR (... AND ...)... #54323 @time-and-fate the TiDB optimizer automatically determines whether to use TiFlash replicas based on the cost estimation. To check whether or not a TiFlash replica is selected, you can use the desc or explain analyze --------+ �→ | Table | Non_unique | Key_name | Seq_in_index | Column_name | �→ Collation | Cardinality | Sub_part | Packed | Null | Index_type | �→ Comment | Index_comment | Visible | Expression | Clustered