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cloud: update maxRCU related content - #24433

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@qqqdan qqqdan commented Oct 12, 2026 •

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Summary by CodeRabbit

  • Documentation
    • Clarified how minimum billed and initial autoscaling capacity are determined in Elastic Mode and Limited Mode.
    • Updated Premium instance setup instructions to describe both modes, their scaling behavior, and Limited Mode’s RCU requirements. Clarified that Baseline RCU does not change the Premium instance’s minimum monthly plan charge.
    • Updated Essential instance guidance for CLOUD.202603.x and later, including the default Elastic Mode configuration; earlier versions require minimum and maximum RCU settings.
    • Added guidance on demand-based scaling and when to consider Premium for workloads that consistently exceed 100,000 RCUs.

@ti-chi-bot 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 12, 2026
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Reviewing files that changed from the base of the PR and between 97ffd61 and a874982.

📒 Files selected for processing (3)
  • tidb-cloud/architecture-concepts.md
  • tidb-cloud/create-tidb-cluster-serverless.md
  • tidb-cloud/premium/create-tidb-instance-premium.md

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📝 Walkthrough
📝 Walkthrough

Walkthrough

The documentation describes RCU billing floors and autoscaling for Elastic Mode and Limited Mode. It updates setup guidance for Essential and Premium instances, including mode defaults and capacity settings.

Changes

RCU Capacity Mode Documentation

Layer / File(s) Summary
Billing RCU concepts
tidb-cloud/architecture-concepts.md
The page describes minimum billing RCU as reserved capacity. It specifies the billing floor for each mode and states that Baseline RCU does not change the Premium instance’s minimum monthly plan charge.
Capacity mode setup guidance
tidb-cloud/create-tidb-cluster-serverless.md, tidb-cloud/premium/create-tidb-instance-premium.md
The Essential instructions describe the Elastic Mode default and 2,000-RCU baseline for later versions, Limited Mode, and requirements for earlier versions. The Premium instructions describe Elastic Mode defaults and Limited Mode capacity rules. The CLI reference bullet is unchanged.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Other

Suggested reviewers: qiancai

Merge Risk: 🔵 Low · up to a8749

The Premium setup and concepts pages give conflicting instructions about whether Elastic Mode requires a maximum RCU, which may confuse instance configuration. Align the concepts guidance as a bounded documentation follow-up.

### Architecture Summary

Architecture risk: 🔵 Low · up to a8749

The change affects 1 system.

Changed systems: tidb-cloud

Architecture concerns
No architecture-level concerns identified.

Review details

Systems and components

  • observed — tidb-cloud (service) was modified; 3 changed files map to changed impact.

Before / after behavior

  • observed — Modified behavior in tidb-cloud/architecture-concepts.md: The minimum billing RCU is described as reserved capacity and the minimum billed amount. The previous unconditional rule tying it to the maximum RCU setting is replaced with mode-specific rules: Elastic Mode uses Baseline RCU as the billing floor and initial autoscaling capacity, while Limited Mode derives the minimum from the maximum RCU setting. The prior claim that sudden spikes are handled up to the specified maximum is removed, and the text states that Baseline RCU does not change the Premium instance’s minimum monthly plan charge.
  • observed — Modified behavior in tidb-cloud/create-tidb-cluster-serverless.md: Essential instances on CLOUD.202603.x or later now default to Elastic Mode, with a fixed 2,000-RCU baseline for minimum billed capacity and initial autoscaling capacity. Limited Mode allows setting a maximum RCU; earlier versions do not support Elastic Mode and require both minimum and maximum RCUs. The RCU guidance now describes scaling based on demand and advises considering Premium when workload demand consistently exceeds 100,000 RCUs, replacing the prior statement that scaling occurs within the specified range.
  • observed — Modified behavior in tidb-cloud/create-tidb-cluster-serverless.md: The TiDB Cloud CLI reference bullet was replaced with identical text; its content is unchanged.
  • observed — Modified behavior in tidb-cloud/premium/create-tidb-instance-premium.md: The capacity instructions replace a single maximum-RCU setting with Elastic Mode, selected by default, and Limited Mode. Elastic Mode uses Baseline RCU as the minimum billed and initial autoscaling capacity, and bills at that baseline when per-minute consumption is lower. Limited Mode scales from 25% of its configured maximum to that maximum; its maximum must be in increments of 100, and its minimum billing amount is the greater of 25% of the configured maximum or 5,000 RCUs.
Pre-merge checks · Passed 4 · Failed 1

Failed Failed checks (1 warning)

Check name Status Explanation Resolution
Description check Warning The description follows the template and selects the v8.5 target, but it leaves the required change summary empty. It does not explain what changed or why. Complete the required “What is changed, added, or deleted?” section with a concise summary of the Elastic Mode, Limited Mode, baseline RCU, and minimum billing RCU documentation updates, including the reason for the changes.
Passed Passed checks (4 passed)
Check name Status Explanation
Docstring Coverage Passed No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check Passed Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check Passed Check skipped because no linked issues were found for this pull request.
Title check Passed The title clearly identifies the main change: updating maxRCU-related documentation content.
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Actionable comments posted: 1


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📥 Commits

Reviewing files that changed from the base of the PR and between ab18bbf and d371dda.

📒 Files selected for processing (3)
  • tidb-cloud/architecture-concepts.md
  • tidb-cloud/create-tidb-cluster-serverless.md
  • tidb-cloud/premium/create-tidb-instance-premium.md

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Comment thread tidb-cloud/architecture-concepts.md Outdated
Comment thread tidb-cloud/architecture-concepts.md Outdated
Comment thread tidb-cloud/architecture-concepts.md Outdated
- For {{{ .essential }}} instances running CLOUD.202603.x or later, **Elastic Mode** is selected by default. In Elastic Mode, you do not set a maximum RCU. Instead, your instance uses a fixed **Baseline RCU** of 2,000 RCUs, which is the minimum number of Request Capacity Units (RCUs) you are billed for and the initial capacity for autoscaling.

- RCUs represent the compute resources provisioned for your workload. TiDB Cloud automatically scales your {{{ .essential }}} instance within this range based on demand.
- For {{{ .essential }}} instances on earlier versions, use **Max RCU Compatibility Mode**, and specify both a minimum and maximum number of RCUs for the instance.

@qiancai qiancai Oct 12, 2026 •

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Suggested change
- For {{{ .essential }}} instances on earlier versions, use **Max RCU Compatibility Mode**, and specify both a minimum and maximum number of RCUs for the instance.
- For {{{ .essential }}} instances running on TiDB v8.5.3 or earlier versions, only **Max RCU Compatibility Mode** is supported, and you need to specify both a minimum and maximum number of RCUs for the instance.

Reason: "Use" suggests that users can select the capacity mode for earlier versions. If the mode is determined by the instance version, describe it as the applicable mode instead.

Comment thread tidb-cloud/premium/create-tidb-instance-premium.md Outdated
@qiancai qiancai self-assigned this Oct 12, 2026
@qiancai qiancai added translation/no-need No need to translate this PR. area/tidb-cloud This PR relates to the area of TiDB Cloud. labels Oct 12, 2026
@ti-chi-bot ti-chi-bot Bot removed the missing-translation-status This PR does not have translation status info. label Oct 12, 2026
Comment thread tidb-cloud/create-tidb-cluster-serverless.md Outdated
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ti-chi-bot Bot commented Oct 12, 2026

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[APPROVALNOTIFIER] This PR is NOT APPROVED

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qqqdan and others added 4 commits October 12, 2026 10:26
Co-authored-by: Grace Cai <qqzczy@126.com>
Co-authored-by: Grace Cai <qqzczy@126.com>
Co-authored-by: Grace Cai <qqzczy@126.com>
@ti-chi-bot ti-chi-bot Bot added 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 13, 2026
Comment thread tidb-cloud/premium/create-tidb-instance-premium.md Outdated
@qiancai qiancai changed the title update maxRCU related content cloud: update maxRCU related content Oct 13, 2026
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