Mysql online backup11/5/2023 When you initiate a migration, the service flushes all tables on the source server with a read lock to obtain the point-in-time snapshot. The undo log is not user controlled, is enabled by default, and does not offer any APIs for control by the user. On executing the Select query (for migration), the source server inspects the current contents of a table, compares it to the Undo log and then rolls back all the changes from the point in time the migration was started, before returning the results to the client. Transactional consistency is achieved through an isolation level of repeatable reads along with the undo log. If another transaction needs to see the original data as part of a consistent read operation, the unmodified data is retrieved from undo log records. An undo log record contains information about how to undo the latest change by a transaction to a clustered index record. The undo log is a collection of undo log records associated with a single read-write transaction. The undo log makes repeatable reads possible and helps generate the snapshot that is required for the migration. With the Enable Transactional Consistency selected, you can maintain data consistency at the target even as traffic continues to the source server. To enable Consistent Backup, select the Enable Transactional Consistency option. Consistent BackupĬonsistent Backup allows data migration to proceed and maintains data consistency regardless of whether the source server is set as read only. As a result, migrated data could be inconsistent because the database snapshots would be read at different points in time. However, if this option is not enabled, there is a possibility for data updates to occur during migration. Making the source server read only prevents users from modifying the data, rendering the database unavailable for any update operations. When you make the source server read only as part of the migration process, the selection applies to all the source server’s databases, regardless of whether they are selected for migration. Selecting this option maintains the data integrity of the target database as the source is migrated by preventing Write/Delete operations on the source server during migration. In the current implementation, users can enable the Make Source Server Read Only option during offline migration. Transactional consistency is achieved without the need to set the source server to read-only mode through this feature. MySQL Consistent Backup is a new feature that allows users to take a Consistent Backup of a MySQL server without losing data integrity at source because of ongoing CRUD (Create, Read, Update, and Delete) operations.
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