Operating System and Environment details

Oct 13, 2025 by wbrum.org 120 views

Bug Report: schemadiff does not recognize change as INSTANT-able when ALGORITHM=INSTANT defined

schemadiff is a powerful tool for schema and change analysis, providing valuable insights into the impact of ALTER TABLE statements on database performance. One of its key features is the ability to predict whether a certain ALTER TABLE statement is eligible for INSTANT DDL, a feature that allows for faster and more efficient database operations. However, a critical issue has been identified that affects the accuracy of this prediction.

When an ALTER TABLE statement includes the algorithm option with a value of instant, as in the following example:

alter table t1 add column i2 int, algorithm=instant

schemadiff fails to recognize this change as INSTANT-able. This is because the algorithm option itself is not being analyzed, leading to a counterintuitive result. In reality, the ALGORITHM=INSTANT option does not invalidate the INSTANT-capability of the ALTER TABLE statement.

The Problem with `alterOptionCapableOfInstantDDL`

The root cause of this issue lies in the alterOptionCapableOfInstantDDL method, which is part of the AlterTableCapableOfInstantDDL class. This method is responsible for determining whether an ALTER TABLE statement is eligible for INSTANT DDL. However, it fails to recognize that the ALGORITHM=INSTANT option does not in itself invalidate the INSTANT-capability.

This is a critical flaw, as it can lead to incorrect predictions about the impact of ALTER TABLE statements on database performance. As a result, database administrators may be misled into believing that certain changes are not eligible for INSTANT DDL, when in fact they are.

Reproduction Steps

To reproduce this issue, follow these steps:

Create a test database with a table t1.
Run the following ALTER TABLE statement:

alter table t1 add column i2 int, algorithm=instant

Use schemadiff to analyze the change and determine whether it is eligible for INSTANT DDL.
Observe that schemadiff fails to recognize the change as INSTANT-able.

Binary Version

The binary version of the affected system is:

current, 21

Operating System and Environment details

The operating system and environment details are:

Log Fragments

The log fragments are:

Conclusion

In conclusion, the schemadiff tool fails to recognize changes as INSTANT-able when the ALGORITHM=INSTANT option is defined. This is due to a critical flaw in the alterOptionCapableOfInstantDDL method, which fails to recognize that the ALGORITHM=INSTANT option does not invalidate the INSTANT-capability. This issue can lead to incorrect predictions about the impact of ALTER TABLE statements on database performance, and can have significant consequences for database administrators.

Recommendations

To resolve this issue, the following recommendations are made:

Update the alterOptionCapableOfInstantDDL method to correctly recognize that the ALGORITHM=INSTANT option does not invalidate the INSTANT-capability.
Test the updated method to ensure that it correctly identifies changes as INSTANT-able.
Deploy the updated schemadiff tool to production environments to ensure that database administrators have accurate information about the impact of ALTER TABLE statements on database performance.

By following these recommendations, database administrators can ensure that their databases are optimized for performance and that they have accurate information about the impact of changes on database performance.
Frequently Asked Questions (FAQs) about the Bug Report: schemadiff does not recognize change as INSTANT-able when ALGORITHM=INSTANT defined

Q: What is the issue with `schemadiff`?

A: The issue with schemadiff is that it fails to recognize changes as INSTANT-able when the ALGORITHM=INSTANT option is defined. This is due to a critical flaw in the alterOptionCapableOfInstantDDL method, which fails to recognize that the ALGORITHM=INSTANT option does not invalidate the INSTANT-capability.

Q: What is the impact of this issue?

A: The impact of this issue is that database administrators may be misled into believing that certain changes are not eligible for INSTANT DDL, when in fact they are. This can lead to incorrect predictions about the impact of ALTER TABLE statements on database performance, and can have significant consequences for database administrators.

Q: How can I reproduce this issue?

A: To reproduce this issue, follow these steps:

Create a test database with a table t1.
Run the following ALTER TABLE statement:

alter table t1 add column i2 int, algorithm=instant

Use schemadiff to analyze the change and determine whether it is eligible for INSTANT DDL.
Observe that schemadiff fails to recognize the change as INSTANT-able.

Q: What is the binary version of the affected system?

A: The binary version of the affected system is:

current, 21

Q: What are the operating system and environment details?

A: The operating system and environment details are:

Q: What are the log fragments?

A: The log fragments are:

Q: How can I resolve this issue?

A: To resolve this issue, the following recommendations are made:

Update the alterOptionCapableOfInstantDDL method to correctly recognize that the ALGORITHM=INSTANT option does not invalidate the INSTANT-capability.
Test the updated method to ensure that it correctly identifies changes as INSTANT-able.
Deploy the updated schemadiff tool to production environments to ensure that database administrators have accurate information about the impact of ALTER TABLE statements on database performance.

Q: What are the benefits of resolving this issue?

A: The benefits of resolving this issue are:

Accurate predictions about the impact of ALTER TABLE statements on database performance.
Improved database performance and efficiency.
Reduced risk of incorrect predictions and subsequent database issues.

Q: Who can help me resolve this issue?

A: If you need help resolving this issue, you can contact the following:

Database administrators and support teams.
MySQL and MariaDB documentation and community resources.
Professional services and consulting firms specializing in database performance and optimization.

By following these FAQs, you can better understand the issue with schemadiff and take steps to resolve it, ensuring accurate predictions about the impact of ALTER TABLE statements on database performance.