SchemaChangeRiskEngine (SCRE):

A tool for assessing the risk of schema changes in a MySQL database when using tools like gh-ost or flywheel.

The problem

Based on Impact analysis of database schema changes and real world learning. It was found we should restrict riskier changes and patterns.

Such patterns include:

• BLOB & TEXT column overuse and storage/memory waste
• ENUM columns issues with casting during value parsing of a change
• SET columns issues with casting during value parsing of a change
• Foreign Key and Trigger usage preventing non-blocking and non-atomic changes
• No Primary Key causing slow migration or table level locking verses row level locking
• Renaming columns and tables leading toward application, data warehouse, and data lake sync issues

The solution

This tool addresses this by allowing you to pass any CREATE or ALTER statement, and it will return a boolean if it's safe.

Example

from schema_change_risk_engine import SchemaChangeRiskEngine as SCRE

engine = SCRE()
changeStatements = [
    """
        CREATE TABLE `test` (
        `id` int(11) NOT NULL AUTO_INCREMENT,
        `name` varchar(255) NOT NULL,
        PRIMARY KEY (`id`)
        )
        ENGINE=InnoDB
        DEFAULT CHARSET=utf8mb4
        COLLATE=utf8mb4_0900_ai_ci
    """,
    "ALTER TABLE `test` ADD COLUMN `age` int(11) NOT NULL DEFAULT 0",
    "ALTER TABLE `test` RENAME COLUMN `age` to `years_old`",
    "ALTER TABLE `test` ADD COLUMN `gener` ENUM('M', 'F','T','NC') NOT NULL DEFAULT 'NC'",
    "ALTER TABLE `test` ADD COLUMN `hobbies` SET('S', 'R','T','NC') NOT NULL DEFAULT 'NC'",
    "ALTER TABLE `test` ADD COLUMN `bio` TEXT NOT NULL",
    "ALTER TABLE `test` ADD COLUMN `photo` BLOB NOT NULL",
    "ALTER TABLE `test` ADD COLUMN `order_date` DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP",
    "ALTER TABLE `test` ADD TRIGGER `test_trigger` AFTER INSERT ON `test` FOR EACH ROW BEGIN INSERT INTO `test` (`name`) VALUES ('test'); END",
    "ALTER TABLE `test` ADD FOREIGN KEY (`id2`) REFERENCES `test` (`id`)",
    "ALTER TABLE `test` RENAME TO `test2`",
    "ALTER TABLE `test` RENAME TABLE `test2` TO `test`"
]

> for idx, change in enumerate(changeStatements):
    print("Statement %s: %s" % (idx + 1, engine.validate(change)))

Statement
1: (True, None)
Statement
2: (True, None)
Statement
3: (False, 'Renaming columns is not allowed')
Statement
4: (False, 'ENUM data type is not allowed')
Statement
5: (False, 'SET is not allowed')
Statement
6: (False, 'TEXT columns are not allowed')
Statement
7: (False, 'BLOB columns are not allowed')
Statement
8: (False, 'DATETIME data type is not allowed')
Statement
9: (False, 'Triggers are not allowed')
Statement
10: (False, 'Foreign keys are not allowed')
Statement
11: (False, 'Renaming tables is not allowed')
Statement
12: (False, 'Renaming tables is not allowed')