ticdc: add new doc to describe the capacity of ticdc data syncing

[hongyunyan]

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[gemini-code-assist]

Hello @hongyunyan, 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!

Summary of Changes

Hello team, Gemini here, providing a summary of this pull request to help everyone quickly understand the changes. This PR introduces a new documentation page specifically for TiCDC, detailing its data synchronization capabilities. The goal is to provide users with a clear understanding of what TiCDC can and cannot synchronize, covering aspects like supported statement types (DDL, DML), handling of system tables and temporary tables, index and foreign key synchronization, and consistency guarantees.

Highlights

• New Documentation: Adds a new markdown file (ticdc/ticdc-data-sync-capabilities.md) dedicated to explaining TiCDC's data synchronization capabilities.
• TiCDC Principles Explained: The document provides background on how TiCDC works, including monitoring Raft Logs, generating logical operations, and its consistency guarantees (eventual consistency, redo log, syncpoint).
• Supported/Unsupported Sync Items: Clearly lists what TiCDC synchronizes (DDL, DML) and what it does not (DQL, DCL, system tables, temporary tables).
• Index and Foreign Key Handling: Explains how TiCDC handles index creation/addition DDLs (asynchronously for TiDB downstream) and foreign key constraint DDLs, noting that it does not synchronize system variables like foreign_key_checks.
• Downstream Constraint Checking: Mentions that TiCDC checks internal integrity but does not validate changes against downstream constraints, reporting errors if constraints are violated during writing.

Changelog

• ticdc/ticdc-data-sync-capabilities.md
  • Added a new documentation file explaining TiCDC's data synchronization capabilities.
  • Detailed the background and principles of TiCDC's data capture.
  • Listed supported and unsupported types of statements and tables for synchronization.
  • Described how index and foreign key DDLs are handled.
  • Clarified TiCDC's role regarding downstream constraint checking.

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[gemini-code-assist]

Code Review

This pull request introduces a new document detailing TiCDC's data synchronization capabilities. The document is well-structured and provides valuable information for users. I've identified a few areas for improvement, mostly related to minor style and formatting, along with a broken link that needs fixing. Overall, good work on creating this informative piece!

I've based my review on the provided style guide, focusing on:

• Correct English grammar, spelling, and punctuation (Style Guide lines 20, 55-57).
• Writing in the second person ("you") when addressing users (Style Guide line 22).
• Avoiding unnecessary words (Style Guide line 24).
• Using sentence case for headings (Style Guide line 32).
• Using ordered lists for steps (Style Guide line 33).
• Ensuring code snippets are in backticks (Style Guide line 34).
• Adding a blank line before and after headings and lists (Style Guide line 38).

Summary of Findings

• Broken Link: A link to storage services on line 19 is missing a closing parenthesis, which will cause the link to fail.
• Spelling Error: The heading on line 8, "Backgroud", should be corrected to "Background".
• Style Guide Adherence: Minor adjustments are suggested for conciseness (lines 3, 17, 27) and addressing the user in the second person (line 29) as per the style guide.
• Formatting: An extra blank line between list items (line 13) could be removed for better compactness. A newline character is recommended at the end of the file (line 31).

Merge Readiness

The document is well-written and informative. However, there is a high-severity issue with a broken link (line 19) and a medium-severity spelling mistake (line 8) that should be addressed before merging. Other suggestions are minor and aim to improve clarity and adherence to the style guide. I am unable to approve pull requests, but I recommend making these changes for a better user experience.

[gemini-code-assist]

There's an extra blank line here between list items 1 and 2. While markdown is flexible, removing it would make the list formatting more consistent and compact. ¹

Style Guide References

Footnotes

1. Style guide recommends a blank line before and after lists, implying the entire list block. Consistent spacing within the list improves readability. (link) ↩

[gemini-code-assist]

It's a common convention to have a newline character at the end of text files. Could we add one here for consistency and to prevent potential issues with some tools?

Suggested change

	5. TiCDC only checks the integrity of the upstream changes received internally, and does not participate in checking whether the data changes meet the various downstream constraints. If a data change that does not meet the downstream constraints is encountered, TiCDC will report an error when writing downstream.
	5. TiCDC only checks the integrity of the upstream changes received internally, and does not participate in checking whether the data changes meet the various downstream constraints. If a data change that does not meet the downstream constraints is encountered, TiCDC will report an error when writing downstream.

[ti-chi-bot]

@gemini-code-assist[bot]: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

Code Review

This pull request introduces a new document detailing TiCDC's data synchronization capabilities. The document is well-structured and provides valuable information for users. I've identified a few areas for improvement, mostly related to minor style and formatting, along with a broken link that needs fixing. Overall, good work on creating this informative piece!

I've based my review on the provided style guide, focusing on:

• Correct English grammar, spelling, and punctuation (Style Guide lines 20, 55-57).
• Writing in the second person ("you") when addressing users (Style Guide line 22).
• Avoiding unnecessary words (Style Guide line 24).
• Using sentence case for headings (Style Guide line 32).
• Using ordered lists for steps (Style Guide line 33).
• Ensuring code snippets are in backticks (Style Guide line 34).
• Adding a blank line before and after headings and lists (Style Guide line 38).

Summary of Findings

• Broken Link: A link to storage services on line 19 is missing a closing parenthesis, which will cause the link to fail.
• Spelling Error: The heading on line 8, "Backgroud", should be corrected to "Background".
• Style Guide Adherence: Minor adjustments are suggested for conciseness (lines 3, 17, 27) and addressing the user in the second person (line 29) as per the style guide.
• Formatting: An extra blank line between list items (line 13) could be removed for better compactness. A newline character is recommended at the end of the file (line 31).

Merge Readiness

The document is well-written and informative. However, there is a high-severity issue with a broken link (line 19) and a medium-severity spelling mistake (line 8) that should be addressed before merging. Other suggestions are minor and aim to improve clarity and adherence to the style guide. I am unable to approve pull requests, but I recommend making these changes for a better user experience.

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[ti-chi-bot]

@hongyunyan: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-verify	4678d32	link	true	/test pull-verify

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