sys var: consider global sort for tidb_ddl_reorg_max_write_speed (#21643)
#21669
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Summary of Changes
Hello @ti-chi-bot, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request enhances the documentation for the tidb_ddl_reorg_max_write_speed system variable, providing crucial clarity on its behavior, particularly when TiDB's Global Sort feature is active. The update includes an example to better illustrate how this variable influences write bandwidth during index backfilling in various cluster configurations.
Highlights
- Clarified Scope of System Variable: The documentation for
tidb_ddl_reorg_max_write_speednow explicitly states that this variable limits the write bandwidth from a single TiDB node to a single TiKV node during index backfilling. - Impact of Global Sort: A new note has been added to explain that when Global Sort is enabled, multiple TiDB nodes can write to TiKV concurrently, which can significantly increase the overall effective write bandwidth.
- Illustrative Example: An example is provided to demonstrate how the
tidb_ddl_reorg_max_write_speedsetting translates to total write bandwidth in a multi-TiDB node cluster, differentiating between scenarios where Global Sort is enabled or disabled.
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Code Review
This pull request updates the documentation for the tidb_ddl_reorg_max_write_speed system variable to clarify its behavior, especially when Global Sort is enabled. An example is added to illustrate the impact of Global Sort on the total write bandwidth. My review focuses on improving the clarity and precision of the new example text.
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/approve |
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[APPROVALNOTIFIER] This PR is APPROVED This pull-request has been approved by: qiancai The full list of commands accepted by this bot can be found here. The pull request process is described here
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This is an automated cherry-pick of #21643
What is changed, added or deleted? (Required)
Which TiDB version(s) do your changes apply to? (Required)
Tips for choosing the affected version(s):
By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.
For details, see tips for choosing the affected versions (in Chinese).
What is the related PR or file link(s)?
tidb_ddl_reorg_max_write_speeddocs-cn#20334Do your changes match any of the following descriptions?