This topic describes how to migrate data between ApsaraDB for Redis instances by using Data Transmission Service (DTS).

Prerequisites

  • The source and destination ApsaraDB for Redis instances are created.
    Note
  • The available storage space of the destination ApsaraDB for Redis instance is larger than the total size of the data in the source ApsaraDB for Redis instance.

Limits

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.
  • Limits on migrating a standalone ApsaraDB for Redis instance to an ApsaraDB for Redis cluster instance: Each command can be run only on a single slot in an ApsaraDB for Redis cluster instance. If you perform operations on multiple keys in the source database and the keys belong to different slots, an error occurs.
    CROSSSLOT Keys in request don't hash to the same slot
    We recommend that you perform operations on only one key during data migration. Otherwise, the migration task will be interrupted.
Other limits
  • ApsaraDB for Redis Enhanced Edition instances (storage-optimized instances) cannot be used as the source and destination databases.
  • 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.

Migration types

Migration type Description
Full data migration

DTS migrates historical data of the required objects from the source database to the destination database.

Incremental data migration

After full data migration is completed, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows you to ensure service continuity when you migrate data between self-managed databases.

Commands that are supported by incremental data migration

  • APPEND
  • BITOP, BLPOP, BRPOP, and BRPOPLPUSH
  • DECR, DECRBY, and DEL
  • EVAL, EVALSHA, EXEC, EXPIRE, and EXPIREAT
  • FLUSHALL and FLUSHDB
  • GEOADD and GETSET
  • HDEL, HINCRBY, HINCRBYFLOAT, HMSET, HSET, and HSETNX
  • INCR, INCRBY, and INCRBYFLOAT
  • LINSERT, LPOP, LPUSH, LPUSHX, LREM, LSET, and LTRIM
  • MOVE, MSET, MSETNX, and MULTI
  • PERSIST, PEXPIRE, PEXPIREAT, PFADD, PFMERGE, PSETEX, and PUBLISH
  • RENAME, RENAMENX, RESTORE, RPOP, RPOPLPUSH, RPUSH, and RPUSHX
  • SADD, SDIFFSTORE, SELECT, SET, SETBIT, SETEX, SETNX, SETRANGE, SINTERSTORE, SMOVE, SPOP, SREM, and SUNIONSTORE
  • ZADD, ZINCRBY, ZINTERSTORE, ZREM, ZREMRANGEBYLEX, ZUNIONSTORE, ZREMRANGEBYRANK, and ZREMRANGEBYSCORE

Procedure

  1. Go to the Data Migration Tasks page.
    1. Log on to the DMS console.
    2. In the top navigation bar, move the pointer over DTS.
    3. Choose DTS (DTS) > Data Migration.
  2. In the drop-down list next to Data Migration Tasks, select the region in which your data migration instance resides.
    Note If you use the new DTS console, you must select the region in which your data migration instance resides in the upper-left corner.
  3. Click Create Task. On the page that appears, configure the source and destination databases.
    Section Parameter Description
    N/A Task Name

    DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to use a unique task name.

    Source Database Select Instance
    Select whether to use an existing instance.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must configure the following parameters.
    Database Type Select Tair/Redis.
    Access Method Select Alibaba Cloud Instance. In this example, the source and destination databases are ApsaraDB for Redis instances. You can also follow the procedure to configure data migration tasks for other types of databases.
    Instance Region The region where the source ApsaraDB for Redis instance resides.
    Replicate Data Across Alibaba Cloud Accounts Specifies whether data is replicated across Alibaba Cloud accounts. In this example, No is selected.
    Instance ID The ID of the source ApsaraDB for Redis instance.
    Database Password The database password of the source ApsaraDB for Redis instance. The database account that corresponds to the password must have the read permissions. If you forget the password, you can reset the password. For more information, see Change or reset the password.
    • If you use the default account whose username is the same as the instance ID, you can enter only the password.
    • If you create a custom account, you must specify the password in the <Custom account>:<Password> format. Example: testaccount:Test1234.
    Note This parameter is optional and can be left empty if no database password is set.
    Destination Database Select Instance
    Select whether to use an existing instance.
    • If you use an existing instance, DTS automatically applies the parameter settings of the instance.
    • If you do not use an existing instance, you must configure the following parameters.
    Database Type Select Tair/Redis.
    Access Method Select Alibaba Cloud Instance.
    Instance Region The region where the destination ApsaraDB for Redis instance resides.
    Instance ID The ID of the destination ApsaraDB for Redis instance.
    Database Password The database password of the destination ApsaraDB for Redis instance. The database account that corresponds to the password must have the read permissions. If you forget the password, you can reset the password. For more information, see Change or reset the password.
    • If you use the default account whose username is the same as the instance ID, you can enter only the password.
    • If you create a custom account, you must specify the password in the <Custom account>:<Password> format. Example: testaccount:Test1234.
  4. In the lower part of the page, click Test Connectivity and Proceed.
    Warning
    • If the source or destination database instance is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the database instance. If the source or destination database instance is a self-managed database hosted on Elastic Compute Service (ECS), DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database that is deployed in data centers or provided by third-party cloud service providers, you must manually add the CIDR blocks of DTS servers to allow DTS to access the database.
    • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database instance or ECS security group rules, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhance the security of your account and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
    • After the DTS task is completed or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist of the database instance or ECS security group rules.
  5. Select objects for the task and configure advanced settings.
    • Basic Settings
      Parameter Description
      Task Stages Select Full Data Migration and Incremental Data Migration.

      For more information, see Migration types.

      Processing Mode of Conflicting Tables
      • Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain identical table names, the precheck is passed. Otherwise, an error is returned during precheck and the data migration task cannot be started.

      • Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases.
        Warning If you select Ignore Errors and Proceed, data consistency is not guaranteed and your business may be exposed to potential risks.
        • If the source and destination databases have the same schema, DTS does not migrate data records that have the same primary keys as data records in the destination database.
        • If the source and destination databases have different schemas, only specific columns are migrated or the data migration task fails.
      Source Objects

      Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.

      Note You can select databases as the objects to be migrated. Keys cannot be selected as objects to be migrated.
      Selected Objects
      • The objects that you select to be migrated. In this scenario, you cannot rename the objects.
      • In the Selected Objects section, right-click an object. In the dialog box that appears, select the commands that you want to migrate. For more information, see Commands that are supported by incremental data migration.
    • Advanced Settings
      Parameter Description
      Set Alerts
      Specify whether to set alerts for the data migration task. If the task fails or the migration latency exceeds the threshold, the alert contacts will receive notifications.
      • Select No if you do not want to set alerts.
      • Select Yes to set alerts. In this case, you must also set the alert threshold and alert contacts.
      Retry Time for Failed Connections
      The retry time range for failed connections. If the data migration task fails, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 120. We recommend that you set the parameter to a value greater than 30. If DTS reconnects to the source and destination databases within the specified time range, DTS resumes the data migration task. Otherwise, the data migration task fails.
      Note
      • If an instance serves as the source database of multiple data migration tasks, the less value of this parameter that is set for the instance takes precedence.
      • When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time range based on your business requirements. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.
      Extend Expiration Time of Destination Database Key
      The extended time period for keys migrated from the source database to the destination instance to remain valid. Unit: seconds. If specific commands are used, such as the following commands, we recommend that you set the parameter to 600 to ensure data consistency:
      expire key seconds
      pexpire key milliseconds
      expireat key timestamp
      pexpireat key timestampMs
      Configure ETL
      Specify whether you want to enable the ETL feature. For more information, see What is ETL?.
      • If you select Yes, the ETL feature is enabled. You must specify a policy in the text box.
      • If you select No, the ETL feature is disabled.
  6. In the lower part of the page, click Next: Save Task Settings and Precheck.
    Note
    • Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
    • If the task fails to pass the precheck, you can click the Info icon icon next to each failed item to view details.
      • You can troubleshoot the issues based on the causes and run a precheck again.
      • If you do not need to troubleshoot the issues, you can ignore failed items and run a precheck again.
  7. Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.
  8. On the Purchase Instance page, specify the Instance Class parameter for the data migration instance. The following table describes the parameter.
    Section Parameter Description
    Parameters Instance Class

    DTS provides several instance classes that have different performance in migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

  9. Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
  10. Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.