Recently, we identified a potential defect in the skip scan feature of MySQL 8.0 in the open-source community. To ensure the stability of your operations, we recommend that you consider either disabling this feature or upgrading your instance minor engine version to mitigate potential issues. Here are the details:

• Affected Product: ApsaraDB RDS for MySQL - Certain historical versions of MySQL 8.0 (minor engine version range: 20190601 to 20230914)
• Impact Explanation: For database instances using the above minor engine versions, if SQL queries rely on the skip scan optimization and if the table contains a large amount of data, there is a very small risk (less than 0.01%) of data truncation, which may lead to incomplete query results.
• Solutions and Recommendations:
  • Option 1: Upgrade the Instance Minor Engine Version: This issue has been resolved in the latest minor engine version. We recommend updating to the latest version. Please check documentation for detailed minor version upgrade guide.
  • Option 2: Disable the Skip Scan Feature: You can disable this feature by modifying the instance parameters through the console. The specific steps are as follows:
    • Steps: Navigate to Instance Details > Parameters in the console. Check the value of loose_optimizer_switch. If the value includes skip_scan=off, this indicates that the feature is disabled. If the value is skip_scan=on or if the relevant content cannot be found, it indicates that the feature is currently enabled.
    • Performance Considerations: If you choose to disable the skip scan feature, please be aware that this may alter the execution plans for some queries and affect query performance. For example, queries based on composite indexes may switch to full table scans when the skip scan feature is disabled, leading to performance degradation. We recommend that you thoroughly evaluate and test your options based on your specific business needs to determine the best course of action.

If you have any questions, please feel free to submit a support ticket to contact us.

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