Lockless schema evolution lets DMS execute Data Definition Language (DDL) changes on MySQL tables without acquiring table locks, keeping your database available during schema changes. Enable it per instance before using the feature.
Prerequisites
Before you begin, make sure you have:
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A supported database type: RDS MySQL, PolarDB for MySQL, MyBase MySQL, or another MySQL source
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An instance with the control mode set to Stable Change or Security Collaboration — View the control mode
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The DBA or administrator role — View my system roles
Enable lockless schema evolution
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Log on to the DMS console V5.0.
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On the console home page, in the Database Instances list, right-click the target instance and select Enable Lockless Schema Evolution.
Alternatively, in the top menu bar, choose Data Asset > Instance Management. On the instance list tab, click More > Edit Instance to the right of the target instance, then enable lockless schema evolution in the Advanced Information section.
In the dialog, select a change method:
Option Description Notes DMS Lockless Change Execution Uses DMS's proprietary DDL lockless engine to prevent table locking. Runs slightly longer than native MySQL Online DDL. Does not affect replication behavior; low risk of primary/standby latency. Native Lockless First, Fallback to DMS on Failure Attempts native Online DDL first. If DMS detects that native execution will lock the table or fail, it automatically switches to the DMS lockless engine. Runs faster overall. May cause parallel replication to degrade to serial replication, which can lead to primary/standby latency. Shut Down Sends the native statement to MySQL without any processing. None When DMS lockless change is not applied
Even with DMS Lockless Change Execution selected, the system falls back to native lockless execution in these cases:
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The target table is empty. Native execution is risk-free and faster on empty tables.
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The SQL statement adds a UNIQUE constraint (UK). Adding a UK is not supported by the DMS lockless schema evolution design.
If DMS detects that native lockless execution would lock the table or cause an error during a fallback, the task fails.
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Click Confirm in the Modify Lockless Schema Evolution dialog box.
What's next
After enabling lockless schema evolution for the instance, implement lockless schema evolution using a lockless change ticket.
When you submit the following ticket types for this instance, DMS prioritizes the lockless schema evolution method automatically:
For general data change tickets, lockless change applies only when the data source is specified by database. If the ticket specifies the data source by instance, the system falls back to native execution, even if lockless schema evolution is enabled for the instance.