tidb: update tidb_index_serial_scan_concurrency docs by 0xPoe · Pull Request #21938 · pingcap/docs

0xPoe · 2025-10-20T09:04:31Z

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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 The variable is no longer modifiable, and its functionality has been replaced by tidb_executor_concurrency for sequential index scans and tidb_analyze_distsql_scan_concurrency for ANALYZE operations.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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0xPoe

🔢 Self-check (PR reviewed by myself and ready for feedback)

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Pull Request Overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

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0xPoe · 2025-10-27T10:22:39Z

/cc @terry1purcell

ti-chi-bot · 2025-10-27T10:22:41Z

@0xPoe: GitHub didn't allow me to request PR reviews from the following users: terry1purcell.

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0xPoe

self-check

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

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

Signed-off-by: 0xPoe <techregister@pm.me>

qiancai

Rest LGTM

qiancai · 2026-04-20T10:46:06Z


-#### `tidb_distsql_scan_concurrency`
+Used to control the concurrency for saving analyze results (writing TopN and histograms to system tables). The default value is `2`. The default value is `1` for v7.4.0 and earlier versions.



Does tidb_analyze_partition_concurrency only take effect on partitioned tables, as "partition" is included in the variable name?

No, it also affects other non-partitioned tables. The name is poor and confusing. We plan to merge and deprecate this in the near future.

ti-chi-bot · 2026-04-20T10:49:30Z

[LGTM Timeline notifier]

Timeline:

2026-04-20 10:49:30.638028214 +0000 UTC m=+1990175.843388261: ☑️ agreed by qiancai.

Co-authored-by: Grace Cai <qqzczy@126.com>

ti-chi-bot · 2026-04-28T08:40:15Z

[APPROVALNOTIFIER] This PR is NOT APPROVED

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Co-authored-by: Grace Cai <qqzczy@126.com>

ti-chi-bot · 2026-04-28T14:15:30Z

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

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0xPoe requested a review from terry1purcell November 3, 2025 09:08

0xPoe commented Mar 25, 2026

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0xPoe and others added 8 commits March 25, 2026 09:57

Update system-variables.md

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

Update system-variables.md

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Update statistics.md

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Update statistics.md

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fix: update

9d1de3a

fix: address comments

04cc842

fix: correct the output

7eebdb3

Signed-off-by: 0xPoe <techregister@pm.me>

0xPoe force-pushed the poe-patch-update-vars branch from 898ec85 to 7eebdb3 Compare March 25, 2026 08:58

qiancai self-assigned this Mar 25, 2026

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Update system-variables.md

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Co-authored-by: Grace Cai <qqzczy@126.com>

0xPoe and others added 12 commits April 28, 2026 10:40

Update statistics.md

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winoros approved these changes Apr 28, 2026

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		#### `tidb_distsql_scan_concurrency`
		Used to control the concurrency for saving analyze results (writing TopN and histograms to system tables). The default value is `2`. The default value is `1` for v7.4.0 and earlier versions.

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0xPoe commented Oct 20, 2025 •

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