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v8.5.6 ticdc: add scheduler configuration recommendations for table split mode (#22483) #22501

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12 changes: 11 additions & 1 deletion ticdc/ticdc-architecture.md
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Expand Up @@ -64,7 +64,17 @@ When this feature is enabled, TiCDC automatically splits and distributes tables

> **Note:**
>
> For MySQL sink changefeeds, only tables that meet one of the preceding conditions and have **exactly one primary key or non-null unique key** can be split and distributed by TiCDC, to ensure the correctness of data replication in table split mode.
> For MySQL sink changefeeds, only tables that meet one of the preceding conditions and have **exactly one primary key or non-null unique key** can be split and distributed by TiCDC, to ensure the correctness of data replication in table-level task splitting mode.

### Recommended configurations for table-level task splitting

After switching to the new TiCDC architecture, do not reuse the table-splitting configurations from the classic architecture. In most scenarios, use the default configuration of the new architecture. Make incremental adjustments based on the default values only in special scenarios where replication performance bottlenecks or scheduling imbalance occur.

In table split mode, pay attention to the following settings:

- [`scheduler.region-threshold`](/ticdc/ticdc-changefeed-config.md#region-threshold): the default value is `10000`. When the number of Regions in a table exceeds this threshold, TiCDC splits the table. For tables with relatively few Regions but high overall write throughput, you can reduce this value appropriately. This parameter must be greater than or equal to `scheduler.region-count-per-span`. Otherwise, tasks might be rescheduled repeatedly, which increases replication latency.
- [`scheduler.region-count-per-span`](/ticdc/ticdc-changefeed-config.md#region-count-per-span-new-in-v854): the default value is `100`. During changefeed initialization, tables that meet the split conditions are split according to this parameter. After splitting, each split sub-table contains at most `region-count-per-span` regions.
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low

To improve clarity and use active voice as recommended by the style guide, consider rephrasing this sentence. Also, for consistency with the rest of the document, Regions should be capitalized.

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- [`scheduler.region-count-per-span`](/ticdc/ticdc-changefeed-config.md#region-count-per-span-new-in-v854): the default value is `100`. During changefeed initialization, tables that meet the split conditions are split according to this parameter. After splitting, each split sub-table contains at most `region-count-per-span` regions.
- [`scheduler.region-count-per-span`](/ticdc/ticdc-changefeed-config.md#region-count-per-span-new-in-v854): the default value is `100`. During changefeed initialization, TiCDC splits tables that meet the split conditions according to this parameter. After splitting, each sub-table contains at most `region-count-per-span` Regions.
References
  1. The style guide recommends using active voice over passive voice (line 43) and using consistent terminology (line 25). The suggested change improves on both aspects. (link)

- [`scheduler.write-key-threshold`](/ticdc/ticdc-changefeed-config.md#write-key-threshold): the default value is `0` (disabled). When the sink write throughput of a table exceeds this threshold, TiCDC triggers table splitting. In most cases, keep this parameter to `0`.
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For better readability, at is more idiomatic than to in this context.

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- [`scheduler.write-key-threshold`](/ticdc/ticdc-changefeed-config.md#write-key-threshold): the default value is `0` (disabled). When the sink write throughput of a table exceeds this threshold, TiCDC triggers table splitting. In most cases, keep this parameter to `0`.
- [`scheduler.write-key-threshold`](/ticdc/ticdc-changefeed-config.md#write-key-threshold): the default value is `0` (disabled). When the sink write throughput of a table exceeds this threshold, TiCDC triggers table splitting. In most cases, keep this parameter at `0`.
References
  1. The style guide recommends correcting grammar mistakes for better readability (line 20). (link)


## Compatibility

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5 changes: 5 additions & 0 deletions ticdc/ticdc-changefeed-config.md
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Expand Up @@ -163,6 +163,11 @@ For more information, see [Event filter rules](/ticdc/ticdc-filter.md#event-filt
- The value is `false` by default. Set it to `true` to enable this feature.
- Default value: `false`

#### `region-count-per-span` <span class="version-mark">New in v8.5.4</span>

- Introduced in the [TiCDC new architecture](/ticdc/ticdc-architecture.md). During changefeed initialization, tables that meet the split conditions are split according to this parameter. After splitting, each split sub-table contains at most `region-count-per-span` Regions.
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To improve clarity and use active voice as recommended by the style guide, consider rephrasing this sentence.

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- Introduced in the [TiCDC new architecture](/ticdc/ticdc-architecture.md). During changefeed initialization, tables that meet the split conditions are split according to this parameter. After splitting, each split sub-table contains at most `region-count-per-span` Regions.
- Introduced in the [TiCDC new architecture](/ticdc/ticdc-architecture.md). During changefeed initialization, TiCDC splits tables that meet the split conditions according to this parameter. After splitting, each sub-table contains at most `region-count-per-span` Regions.
References
  1. The style guide recommends using active voice over passive voice (line 43) and avoiding unnecessary words (line 24). The suggested change improves on both aspects. (link)

- Default value: `100`
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Please remove the trailing space for consistent formatting.

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- Default value: `100`
- Default value: `100`
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  1. The style guide recommends correcting grammar, spelling, and punctuation mistakes (line 20), which extends to minor formatting issues like trailing spaces. (link)


#### `region-threshold`

- Default value: for the [TiCDC new architecture](/ticdc/ticdc-architecture.md), the default value is `10000`; for the [TiCDC classic architecture](/ticdc/ticdc-classic-architecture.md), the default value is `100000`.
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