Java.DBMigrationTools.What happens when a migration fails?

✅ Short Answer

When a migration fails:

• The migration process stops immediately
• The failed changeset is not marked as executed
• Any partial changes already applied by that changeset remain in the database unless you handle rollback manually

❗ No automatic rollback is performed unless you explicitly define and run one.

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🔎 Liquibase – What happens on failure?

🔹 Suppose you run:

liquibase update

🔹 Scenario:

One of your changesets (e.g. id=3) has a syntax error or constraint violation.

🔸 What happens:

• Liquibase stops at the error.
• That changeset is not marked as executed in DATABASECHANGELOG
• Previous changesets remain applied
• Partial SQL from the failed changeset may have affected the DB, depending on DB settings and the operation

✅ You can:

• Fix the issue
• Re-run liquibase update (it will skip changesets already marked as executed)

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🔹 Example:

<changeSet id="1" author="alice">
  <createTable tableName="users">
    <column name="id" type="bigint" autoIncrement="true"/>
  </createTable>
</changeSet>

<changeSet id="2" author="alice">
  <addColumn tableName="users">
    <column name="email" type="varchar(255)"/>
  </addColumn>
</changeSet>

<changeSet id="3" author="alice">
  <!-- This fails due to bad SQL -->
  <sql>ALTER TABLE users ADD age_in_days_typo INT</sql>
</changeSet>

✅ Changeset 3 fails
✅ Changesets 1 and 2 are marked as executed
❌ 3 is not
❗ You must fix the SQL, then re-run

🔹 Rollback?

Liquibase does not rollback automatically on failure.
You can:

• Define a <rollback> section per changeset
• Manually run:

liquibase rollbackCount 1

But rollback must be explicitly triggered, not automatic.

🔎 Flyway – What happens on failure?

In Flyway:

• The failed script is recorded with a failure status in flyway_schema_history
• The entire migration run is stopped
• You must repair or fix the problem before continuing

✅ Fix the file or write a new script
✅ Then run:

flyway repair  # marks the failed migration as pending or removes bad checksum
flyway migrate

Flyway does not support rollback, so you must clean the database (dev only) or manually fix the schema.

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📌 Key Takeaways

Tool	On Failure	Rollback?	Recovery
Liquibase	Stops, logs error	❌ Manual (unless scripted)	Fix issue → rerun update
Flyway	Stops, logs failure	❌ Not supported natively	Fix + repair + re-run