This topic describes the precautions and limits when you migrate data from a Redis database, such as a self-managed Redis database and an ApsaraDB for Redis database. To ensure that your data migration task runs as expected, read the precautions and limits before you configure the task.

Scenarios of migrating data from a Redis database

You can view the precautions and limits based on the following migration scenarios: Migrate data between Redis databases

Migrate data between Redis databases

Category Description
Limits on the source database
  • Bandwidth requirements: The server to which the source database belongs must have sufficient egress bandwidth. Otherwise, the data migration speed is affected.
  • If you perform only incremental data migration, you must enable the data logging feature. In addition, the append-only file (AOF) logs of the source database must be stored for more than 24 hours.
  • If you perform both full data migration and incremental data migration, you must enable the data logging feature. In addition, the AOF logs of the source database must be stored for at least seven days. After full data migration is completed, you can set the retention period to more than 24 hours. Otherwise, DTS may fail to obtain the AOF logs and the task may fail. In extreme cases, data may be inconsistent or lost. Make sure that you set the retention period of AOF logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability and performance.
  • Limits on operations: If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data will be inconsistent between the source and destination databases. To ensure data consistency, we recommend that you select Full Data Migration and Incremental Data Migration as the migration types.
Other limits
  • If the source or destination database is an ApsaraDB for Redis instance, the disk type of the instance must be local disk rather than cloud disk.
  • If the data eviction policy (maxmemory-policy) of the destination database is not set to noeviction, data may become inconsistent between the source and destination databases.
  • If you run the EVAL or EVALSHA command to call Lua scripts, DTS cannot identify whether these Lua scripts are executed on the destination database. During incremental data migration, the destination database does not explicitly return the execution results of Lua scripts.
  • When you run the PSYNC or SYNC command to transfer data of the LIST type, DTS does not perform the flush operation on the existing data. Therefore, the destination database may contain duplicate data records.
  • If an expiration policy is enabled for some keys in the source database, these keys may not be deleted in a timely manner after they expired. Therefore, the number of keys in the destination database may be less than that in the source database. You can run the info command to view the number of keys in the destination database.
    Note The number of keys that do not have an expiration policy or have not expired is the same in the source and destination databases.
  • To ensure compatibility, the version of the destination Redis database must be the same as or later than the version of the source Redis database.
    Note If the version of the destination database is earlier than the version of the source database, database compatibility issues may occur.
  • Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses read and write resources of the source and destination databases. This may increase the loads of the database servers.
  • During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data migration is completed, the tablespace of the destination database is larger than that of the source database.
  • DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination instance, stop or release the data migration task. You can also run the revoke command to revoke the write permissions from the accounts that are used by DTS to access the destination instance. Otherwise, the data in the source database will overwrite the data in the destination instance after the task is resumed.
  • If both the source and destination databases are ApsaraDB for Redis Community Edition or Enhanced Edition, take note of the following limits: If the database specifications are changed (for example, the specifications are upgraded or the port number is changed), DTS cannot obtain continuous log data and correct connection information. As a result, the data migration task is interrupted. To ensure data consistency, we recommend that you delete the data in the destination database and reconfigure the data migration task after the database specifications are changed.
Special cases If the source database is a self-managed Redis database, take note of the following limits:
  • If you perform a primary/secondary switchover on the source database when the data migration task is running, the task fails.
  • DTS calculates migration latency based on the timestamp of the latest migrated data in the destination database and the current timestamp in the source database. If no data manipulation language (DML) operation is performed on the source database for a long time, the migration latency may be inaccurate. If the latency of the migration task is too high, you can perform a DML operation on the source database to update the latency.
    Note If you select an entire database as the object to be migrated, you can create a heartbeat table. The heartbeat table is updated or receives data every second.