ticdc: update description for param enable-table-across-nodes

[hongyunyan]

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• This PR is translated from: ticdc: update description for param enable-table-across-nodes docs-cn#21295
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[gemini-code-assist]

Summary of Changes

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!

This pull request significantly enhances the TiCDC documentation by clarifying the behavior of table-level task splitting across different sink types and introducing a detailed guide on TiCDC's data synchronization capabilities. These updates aim to provide users with a more accurate and comprehensive understanding of TiCDC's features and operational nuances, particularly concerning parallel replication and data consistency.

Highlights

• Expanded Scope of Table-Level Task Splitting: The documentation for enable-table-across-nodes has been updated to clarify that table-level task splitting now applies to all sink types in the new TiCDC architecture, extending beyond just MySQL sinks.
• MySQL Sink Specific Restriction: A new restriction has been added for MySQL Sink Changefeeds, specifying that only tables with a single primary key or non-null unique key can be split and distributed when enable-table-across-nodes is active, ensuring data synchronization correctness.
• Updated Default Region Threshold: The default region-threshold value in the ticdc-architecture.md document has been adjusted from 100000 to 10000.
• New Data Synchronization Capabilities Document: A comprehensive new document, 'TiCDC's Data Synchronization Capability,' has been introduced. It details TiCDC's background, implementation principles, consistency guarantees, supported downstreams, and specific behaviors regarding DDL, DML, DQL, DCL, foreign keys, and data integrity checks.

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[gemini-code-assist]

Code Review

The pull request updates the description for the enable-table-across-nodes parameter, clarifying its behavior across different TiCDC architectures. It also introduces a new document, ticdc-data-sync-capabilities.md, which comprehensively outlines TiCDC's data synchronization features. The changes enhance the accuracy and completeness of the documentation. However, there is an inconsistency in the default value of region-threshold between two files, and some minor formatting and grammatical improvements are needed in the new document.

I am having trouble creating individual review comments. Click here to see my feedback.

ticdc/ticdc-changefeed-config.md (157)

There's an inconsistency regarding the default value of region-threshold. In ticdc-architecture.md, it states the default is 10000, but here it's 100000. Please clarify and ensure consistency across documentation.

ticdc/ticdc-architecture.md (62)

The default value for scheduler.region-threshold has changed from 100000 to 10000. This is a substantial change and might impact existing configurations or user expectations. It would be beneficial to explicitly mention this change and its potential implications for users migrating from older versions or those who have previously configured this parameter. This is a documentation clarification to ensure users are aware of a breaking change in default behavior.

ticdc/ticdc-data-sync-capabilities.md (8)

There's a typo in the heading. "Backgroud" should be "Background".

## Background

References

1. Correct English grammar, spelling, and punctuation mistakes, if any. ^(link)

ticdc/ticdc-data-sync-capabilities.md (14)

There's an unnecessary blank line here. Please remove it for better formatting.

2. TiCDC generates logical operations (such as INSERT/UPDATE/DELETE) that are equivalent to SQL semantics, rather than restoring the original SQL executed upstream one by one. Refer to [TiCDC's Implementation Principles for Processing Data Changes](/ticdc/ticdc-overview.md#implementation-of-processing-data-changes).

References

1. Add a blank line before and after headings and lists. ^(link)

ticdc/ticdc-data-sync-capabilities.md (29)

The sentence "Therefore, customers need to set appropriate system variables in the downstream to determine whether the downstream foreign key constraint check is enabled." is a bit verbose. Consider rephrasing for conciseness and directness.

Therefore, you need to set appropriate system variables in the downstream to enable or disable foreign key constraint checks.

References

1. Avoid unnecessary words and repetition. ^(link)

ticdc/ticdc-data-sync-capabilities.md (31)

The file is missing a newline at the end. Please add one.

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.

References

1. Correct English grammar, spelling, and punctuation mistakes, if any. ^(link)

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