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tidb: update tidb_index_serial_scan_concurrency docs (#21938) #23264

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tidb: update tidb_index_serial_scan_concurrency docs (#21938) #23264

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874dd8d
This is an automated cherry-pick of #21938
0xPoe Jul 14, 2026
f641277
docs: skip inapplicable release-7.1 cherry-pick
qiancai Jul 15, 2026
4a971d7
docs: adapt cherry-pick for release-7.1
qiancai Jul 15, 2026
5d9e4cd
docs: exclude best practices from release-7.1
qiancai Jul 15, 2026
0f9f58e
docs: retain release-7.1 index scan concurrency
qiancai Jul 15, 2026
fb10d5f
docs: retain release-7.1 OOM concurrency guidance
qiancai Jul 15, 2026
cd3a565
docs: exclude no-op OOM guidance from release-7.1
qiancai Jul 15, 2026
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2 changes: 1 addition & 1 deletion statistics.md
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Expand Up @@ -430,7 +430,7 @@ When you run the `ANALYZE` statement, you can adjust the concurrency using the f

#### `tidb_build_stats_concurrency`

Currently, when you run the `ANALYZE` statement, the task is divided into multiple small tasks. Each task only works on one column or index. You can use the `tidb_build_stats_concurrency` parameter to control the number of simultaneous tasks. The default value is `4`.
This variable controls the concurrency for building statistics during manual `ANALYZE`, such as the number of table or partition analysis tasks that can be processed simultaneously. The default value is `4`.

#### `tidb_distsql_scan_concurrency`

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10 changes: 5 additions & 5 deletions system-variables.md
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Expand Up @@ -967,7 +967,8 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Default value: `1`
- This variable specifies the concurrency of reading and writing statistics for a partitioned table when TiDB analyzes the partitioned table.
- Range: `[1, 18446744073709551615]`
- For manual and auto `ANALYZE`, this variable controls the concurrency for saving `ANALYZE` results, including writing TopN and histograms to system tables.

### tidb_analyze_version <span class="version-mark">New in v5.1.0</span>

Expand Down Expand Up @@ -1028,7 +1029,7 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
- Type: Integer
- Default value: `1`
- Range: `[1, 256]`
- This variable is used to set the concurrency of executing the automatic update of statistics.
- This variable controls the concurrency for building statistics during auto `ANALYZE`, such as the number of table or partition analysis tasks that can be processed simultaneously.

### tidb_backoff_lock_fast

Expand Down Expand Up @@ -1124,8 +1125,7 @@ MPP is a distributed computing framework provided by the TiFlash engine, which a
- Default value: `4`
- Range: `[1, 256]`
- Unit: Threads
- This variable is used to set the concurrency of executing the `ANALYZE` statement.
- When the variable is set to a larger value, the execution performance of other queries is affected.
- This variable controls the concurrency for building statistics during manual `ANALYZE`, such as the number of table or partition analysis tasks that can be processed simultaneously.

### tidb_capture_plan_baselines <span class="version-mark">New in v4.0</span>

Expand Down Expand Up @@ -3225,7 +3225,7 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
- Scope: SESSION | GLOBAL
- Persists to cluster: Yes
- Default value: `1`
- This variable specifies the concurrency of merging statistics for a partitioned table when TiDB analyzes the partitioned table.
- This variable controls the concurrency for merging TopN results of partitioned tables.

### tidb_metric_query_range_duration <span class="version-mark">New in v4.0</span>

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