tidb: update tidb_index_serial_scan_concurrency docs #21938

0xPoe · 2025-10-20T09:04:31Z

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ti-chi-bot · 2025-10-20T09:04:40Z

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Pull Request Overview

This PR updates documentation to reflect the deprecation of the tidb_index_serial_scan_concurrency variable. The variable is no longer modifiable, and its functionality has been replaced by tidb_executor_concurrency for sequential index scans and tidb_analyze_distsql_scan_concurrency for ANALYZE operations.

Key Changes:

Deprecates tidb_index_serial_scan_concurrency with a warning that directs users to the replacement variables
Removes references to the deprecated variable from troubleshooting and performance benchmarking guides
Updates configuration examples to use tidb_analyze_distsql_scan_concurrency instead of the deprecated variables

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
system-variables.md	Adds deprecation warning and updates description to indicate the variable is kept for backward compatibility only
statistics.md	Consolidates documentation by removing the separate section for `tidb_index_serial_scan_concurrency` and updating `tidb_analyze_distsql_scan_concurrency` to note its expanded role
troubleshoot-tidb-oom.md	Removes deprecated variable from the list of concurrency controls for reducing memory usage
tidb-cloud/v8.5-performance-benchmarking-with-tpcc.md	Replaces deprecated variables with `tidb_analyze_distsql_scan_concurrency` in TPC-C test setup
tidb-cloud/v8.1-performance-benchmarking-with-tpcc.md	Replaces deprecated variables with `tidb_analyze_distsql_scan_concurrency` in TPC-C test setup
best-practices/tidb-best-practices.md	Updates reference from deprecated variable to `tidb_executor_concurrency` for controlling index scan behavior

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fix: v8.1 fix: v8.5 fix: tidb_analyze_distsql_scan_concurrency fix: tidb_index_serial_scan_concurrency fix: fix: 8.1 fix: 8.5 fix: update links fix: update fix fix: typo fix: update fix: default value fix: update fix: update fix: update fix: update

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system-variables.md

statistics.md

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0xPoe · 2025-10-27T10:22:39Z

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terry1purcell · 2025-10-27T23:11:14Z

system-variables.md

- This variable is used to set the sampling concurrency in the `ANALYZE` process.
- When the variable is set to a larger value, the execution performance of other queries is affected.
+- Used to control the concurrency level for merging samples collected from different regions.
+- Used to control the concurrency for special indexes (such as indexes on generated virtual columns), for example, how many indexes can collect statistics simultaneously.


This "check warning" is complaining about the word "many" in "how many indexes". You may want to use "for example, the number of indexes which can concurrently collect statistics".

terry1purcell · 2025-10-27T23:12:02Z

system-variables.md

 - 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.
+- For manual analyze: used to control the concurrency of table or partition analysis — for example, how many partition or table tasks can be processed simultaneously.


You may want to use "the number of partitions or table tasks that can be processed simultaneously".

terry1purcell · 2025-10-27T23:12:23Z

system-variables.md

 - Default value: `1`
 - Range: `[1, 256]`
- This variable is used to set the concurrency of executing the automatic update of statistics.
+- For auto analyze: used to control the concurrency of table or partition analysis — for example, how many partition or table tasks can be processed simultaneously.


You may want to use "the number of partitions or table tasks that can be processed simultaneously".

terry1purcell · 2025-10-27T23:12:42Z

statistics.md

 #### `tidb_build_stats_concurrency`

-When you run the `ANALYZE` statement, the task is divided into multiple small tasks. Each task only works on statistics of one column or index. You can use the [`tidb_build_stats_concurrency`](/system-variables.md#tidb_build_stats_concurrency) variable to control the number of simultaneous small tasks. The default value is `2`. The default value is `4` for v7.4.0 and earlier versions.
+Used to control the concurrency of table or partition analysis — for example, how many partition or table tasks can be processed simultaneously. The default value is `2`. The default value is `4` for v7.4.0 and earlier versions.


You may want to use "the number of partitions or table tasks that can be processed simultaneously".

terry1purcell · 2025-10-27T23:13:37Z

statistics.md


-When analyzing ordinary columns, you can use [`tidb_build_sampling_stats_concurrency`](/system-variables.md#tidb_build_sampling_stats_concurrency-new-in-v750) to control the concurrency of executing sampling tasks. The default value is `2`.
+1. Used to control the concurrency level for merging samples collected from different regions.  
+2. Used to control the concurrency for special indexes (such as indexes on generated virtual columns), for example, how many special indexes can collect statistics simultaneously.


You may want to use "the number of special indexes that can collect statistics simultaneously".

ti-chi-bot bot added missing-translation-status This PR does not have translation status info. size/S Denotes a PR that changes 10-29 lines, ignoring generated files. labels Oct 20, 2025

0xPoe requested a review from Copilot October 20, 2025 09:19

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0xPoe changed the title ~~tidb: update tidb_index_serial_scan_concurrency docs~~ WIP: tidb: update tidb_index_serial_scan_concurrency docs Oct 20, 2025

ti-chi-bot bot added do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. size/M Denotes a PR that changes 30-99 lines, ignoring generated files. and removed size/S Denotes a PR that changes 10-29 lines, ignoring generated files. labels Oct 20, 2025

0xPoe changed the title ~~WIP: tidb: update tidb_index_serial_scan_concurrency docs~~ tidb: update tidb_index_serial_scan_concurrency docs Oct 27, 2025

ti-chi-bot bot removed the do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. label Oct 27, 2025

0xPoe force-pushed the poe-patch-update-vars branch from f87d569 to bb45b6d Compare October 27, 2025 10:04

0xPoe commented Oct 27, 2025

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0xPoe and others added 5 commits October 27, 2025 11:07

Update system-variables.md

4e37ca0

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update system-variables.md

09f226a

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update statistics.md

ebdcfb5

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update statistics.md

0e12d5e

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

fix: update

b488ec7

0xPoe requested review from qiancai and time-and-fate October 27, 2025 10:22

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0xPoe commented Oct 20, 2025 •

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