General Usage Suggestions

Before using DRS, you need to understand the following:

• The destination database version must be the same as or later than the source database version.
• The success of migration depends on environment and manual operations. You can run a migration test before you start the full-scale migration to help you detect and resolve problems in advance.
• To maintain data consistency before and after the migration, do not write data to the source and destination databases in the full migration mode. In the full+incremental migration mode, you can continue the migration while data is still being written to the source database.
• When a task is being started or in the full migration phase, do not perform DDL operations on the source database. Otherwise, the task may be abnormal.
• If you read a table, especially a large table, during the full migration, the exclusive lock on that table may be blocked.
• To ensure data consistency, tables to be migrated without a primary key may be locked for 3s.
• The data being migrated may be locked by other transactions for a long period of time, resulting in read timeout.
• Due to the inherent characteristics of MySQL, in some scenarios the performance may be negatively affected. For example, if the CPU resources are insufficient and the storage engine is TokuDB, the read speed on tables may be decreased by 10%.
• When DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.
• If network bandwidth is not limited, the query rate of the source database increases by about 50 MB/s during full migration, and two to four CPUs are occupied.
• For more information about the impact of DRS on databases, see How Does DRS Affect the Source and Destination Databases?
• It is best to start your migration task during off-peak hours by setting Start Time to Start at a specified time. A less active database is easier to migrate successfully and prevents impact on the database performance. If you have to migrate data during peak hours, you can select Yes for Flow Control to adjust the migration speed.

If many-to-one migration is involved, you need to understand the following:

• When creating multiple migration tasks in the many-to-one scenario, ensure that the read and write settings of the destination database are consistent in these tasks. For details, see Constraints and Operation Suggestions on Many-to-One Scenario.

After data migration is complete, you need to understand the following:

• To obtain accurate comparison results, compare data at a specified time point during off-peak hours. If it is needed, select Start at a specified time for Comparison Time. Due to slight time difference and continuous operations on data, inconsistent comparison results may be generated, reducing the reliability and validity of the results.