When a table has a primary key, there is no need to split the RowChangeEvent when update a uk.

[King-Dylan]

What did you do?

Enable the old value feature, then update uk in a table

CREATE TABLE `employee` (
  `id` bigint(20) NOT NULL,
  `catalog_id` bigint(20) NOT NULL,
  `merchant_id` bigint(20) NOT NULL,
  `merchant_item_id` varchar(127) COLLATE utf8mb4_unicode_ci NOT NULL,
  `merchant_item_group_id` varchar(127) COLLATE utf8mb4_unicode_ci NOT NULL,
  `merchant_display_name` varchar(255) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `primary_feed_profile_id` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`) /*T![clustered_index] CLUSTERED */,
  UNIQUE KEY `catalog_id` (`catalog_id`,`primary_feed_profile_id`,`merchant_item_group_id`),
);
insert into employee (id, catalog_id,merchant_id,merchant_item_id,merchant_item_group_id) values (89898989,21211212,12121212,'1212121as','dsdsdsdsdd');
update employee set merchant_item_id='newval',merchant_item_group_id='nzzzzzzzzzzzz11111z' where id=8989898989;

What did you expect to see?

Only one ChangeFeedEvent has been output.

What did you see instead?

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s{"u":{"additional_images":{"t":252,"f":65,"v":null},"adwords_redirect_link":{"t":15,"f":64,"v":null},"age_group":{"t":3,"f":65,"v":null},"api_updated_time":{"t":8,"f":65,"v":null},"availability":{"t":3,"f":65,"v":null},"average_review_rating":{"t":5,"f":65,"v":null},"brand":{"t":15,"f":64,"v":null},"catalog_id":{"t":8,"f":49,"v":21211212},"catalog_id_migration":{"t":8,"f":113,"v":null},"color":{"t":15,"f":64,"v":null},"condition":{"t":3,"f":65,"v":null},"country":{"t":3,"f":113,"v":null},"created_at":{"t":7,"f":1,"v":"2024-06-06 21:29:34"},"currency":{"t":3,"f":65,"v":null},"custom_label_0":{"t":15,"f":64,"v":null},"custom_label_1":{"t":15,"f":64,"v":null},"custom_label_2":{"t":15,"f":64,"v":null},"custom_label_3":{"t":15,"f":64,"v":null},"custom_label_4":{"t":15,"f":64,"v":null},"decayed_click_through":{"t":5,"f":65,"v":null},"decayed_impression":{"t":5,"f":65,"v":null},"feed_updated_time":{"t":8,"f":65,"v":null},"free_shipping_limit":{"t":8,"f":65,"v":null},"gender":{"t":3,"f":65,"v":null},"generated_internal_product_id":{"t":8,"f":65,"v":null},"google_product_categories":{"t":245,"f":65,"v":null},"gtin":{"t":15,"f":64,"v":null},"hyperloop_internal_item_id":{"t":8,"f":65,"v":null},"id":{"t":8,"h":true,"f":11,"v":8989898989},"is_best_seller":{"t":1,"f":65,"v":null},"is_free_shipping_label":{"t":1,"f":65,"v":null},"is_new_arrival":{"t":1,"f":65,"v":null},"is_recommended_product":{"t":1,"f":65,"v":null},"item_description":{"t":15,"f":64,"v":null},"item_description_html":{"t":15,"f":64,"v":null},"link":{"t":15,"f":64,"v":null},"locale":{"t":15,"f":112,"v":null},"main_image":{"t":252,"f":65,"v":null},"material":{"t":15,"f":64,"v":null},"media_links_hash":{"t":254,"f":64,"v":null},"merchant_display_name":{"t":15,"f":64,"v":null},"merchant_id":{"t":8,"f":33,"v":12121212},"merchant_item_group_id":{"t":15,"f":0,"v":"nzzzzzzzzzzzz11111z"},"merchant_item_id":{"t":15,"f":48,"v":"newval11111111"},"mobile_link":{"t":15,"f":64,"v":null},"mpn":{"t":15,"f":64,"v":null},"num_add_to_cart_actions_thirty_days":{"t":3,"f":65,"v":null},"num_ratings":{"t":3,"f":65,"v":null},"num_reviews":{"t":3,"f":65,"v":null},"num_visits_thirty_days":{"t":3,"f":65,"v":null},"overridden_fields":{"t":252,"f":65,"v":null},"pattern":{"t":15,"f":64,"v":null},"pin_id_to_image_signature":{"t":252,"f":65,"v":null},"pin_ids":{"t":245,"f":65,"v":null},"pin_metadata_hash":{"t":254,"f":64,"v":null},"price":{"t":8,"f":65,"v":null},"primary_feed_profile_id":{"t":8,"f":113,"v":null},"product_types":{"t":245,"f":65,"v":null},"sale_price":{"t":8,"f":65,"v":null},"shipping_country":{"t":15,"f":64,"v":null},"size":{"t":15,"f":64,"v":null},"size_system":{"t":3,"f":65,"v":null},"size_type":{"t":3,"f":65,"v":null},"title":{"t":15,"f":64,"v":null},"updated_at":{"t":7,"f":1,"v":"2024-06-06 21:50:34"},"variant_options":{"t":252,"f":65,"v":null},"video_pin_id_to_video_signature":{"t":252,"f":65,"v":null},"videos":{"t":252,"f":65,"v":null}}}

Versions of the cluster

Upstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

(paste TiDB cluster version here)

Upstream TiKV version (execute tikv-server --version):

(paste TiKV version here)

TiCDC version (execute cdc version):

v7.1.4

[CharlesCheung96]

What is the dispatchers configuration?

[King-Dylan]

After PR 9437, we add this feature to split the RowChangeEvent. https://github.com/pingcap/tiflow/blob/release-7.1-20240129-v7.1.2/cdc/model/sink.go#L833-L837 I think we need more jugment conditions to distinguish this scenario.

[CharlesCheung96]

It is reasonable not to split transactions that contain a single update event. However, transactions that rely on sql execution order must be split and sorted to ensure the correctness of the serial consumption. For more information, ref tikv/tikv#17062.