Data Transmission Service:Configure one-way data synchronization between ApsaraDB for Redis instances

Prerequisites

• The versions of the source and destination instances are supported by DTS. For more information, see Overview of data synchronization scenarios.

  Note

  The version of the destination instance must be the same as or later than that of the source instance. If you want to synchronize data between different versions of instances, make sure that the versions of the source and destination instances are compatible. For example, you can create a pay-as-you-go destination instance to check the compatibility between the source and destination instances. Then, you can release this instance or change the billing method of the instance to subscription.

• The available storage space of the destination instance is greater than the total size of the data in the source instance.

• The appendonly parameter is set to yes if an Enhanced Edition (Tair) persistent memory-optimized instance is configured as the source instance.

• No Enhanced Edition (Tair) ESSD-based instance is configured as the source instance.

• The timeout period for data replication between the master and replica nodes in the source instance is specified by the repl-timeout parameter. By default, this parameter is set to 60 seconds. We recommend that you run the config set repl-timeout 600 command to set this parameter to 600 seconds. If the source instance stores a large amount of data, you can increase the value of the repl-timeout parameter based on your business requirements.

Precautions

• DTS uses the resources of the source and destination instances during initial full data synchronization. This may increase the loads on the database servers. If you synchronize a large volume of data or if the server specifications cannot meet your requirements, database services may become unavailable. Before you synchronize data, evaluate the impact of data synchronization on the performance of the source and destination instances. We recommend that you synchronize data during off-peak hours.

• If an expiration policy is enabled for specific keys in the source database, these keys may not be deleted at the earliest opportunity after they expire. 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 the expiration policy enabled or have not expired is the same between the source and destination databases.

• We recommend that you do not run the FLUSHDB or FLUSHALL command on the source instance during data synchronization. Otherwise, data inconsistency may occur between the source and destination instances.

• By default, the maxmemory-policy parameter that specifies how data is evicted is set to volatile-lru for ApsaraDB for Redis instances. If the destination instance has insufficient memory, data inconsistency may occur between the source and destination instances due to data eviction. In this case, the data synchronization task does not stop running.

  To prevent data inconsistency, we recommend that you set maxmemory-policy to noeviction for the destination instance. This way, the data synchronization task fails if the destination instance has insufficient memory, but data loss can be prevented for the destination instance.

  Note

  For more information about data eviction policies, see What is the default eviction policy of ApsaraDB for Redis?

• During data synchronization, if the number of shards in the source instance increases or decreases or if the instance specifications are changed (for example, the memory capacity is scaled up), you must reconfigure the data synchronization task. To ensure data consistency, we recommend that you clear the data that has been synchronized to the destination instance before you reconfigure the data synchronization task.

• During data synchronization, the endpoint of the source instance may be changed. For example, the endpoint of the source instance is changed if the zone of the instance is changed or the network type is changed from classic network to Virtual Private Cloud (VPC). In this case, you must reconfigure the data synchronization task.

• Limits on synchronizing data from 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, the following 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 synchronization. Otherwise, the data synchronization task is interrupted.

• If the destination instance is deployed in a cluster architecture and the amount of memory used by a shard in the destination instance reaches the upper limit, or if the available storage space of the destination instance is insufficient, the data synchronization task fails due to out of memory (OOM).

• If the transparent data encryption (TDE) feature is enabled for the source or destination instance, you cannot use DTS to synchronize data.

Supported synchronization topologies

• One-way one-to-one synchronization

• One-way one-to-many synchronization

• One-way cascade synchronization

For more information, see Synchronization topologies.

Operations that can be synchronized

• APPEND

• BITOP, BLPOP, BRPOP, and BRPOPLPUSH

• DECR, DECRBY, and DEL

• EVAL, EVALSHA, EXEC, EXPIRE, and EXPIREAT

• 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, and PSETEX

• 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

• SWAPDB and UNLINK (supported only if the engine version of the source instance is 4.0)

• XADD, XCLAIM, XDEL, XAUTOCLAIM, XGROUP CREATECONSUMER, and XTRIM

Permissions required for database accounts

Procedure

1. Purchase a data synchronization instance. For more information, see Purchase a data synchronization instance.

   Note

   On the buy page, set both Source Instance and Destination Instance to Redis.

2. Log on to the DTS console.

   Note

   • If you are navigated to the DMS console from the DTS console, you can move the pointer over the icon in the lower-right corner and click the icon to return to the DTS console.

   • If the new version of the DTS console appears after the logon, you can click the icon in the lower-right corner to return to the previous version.

3. In the left-side navigation pane, click Data Synchronization.

4. In the upper part of the Data Synchronization Tasks page, select the region in which the destination instance resides.

5. Find the data synchronization instance and click Configure Task in the Actions column.

6. Configure the source and destination instances.

   Section	Parameter	Description
   N/A	Synchronization Task Name	The task name that DTS automatically generates. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to use a unique task name.
   Source Instance Details	Instance Type	The type of the destination database. Select Redis Instance.
   	Instance Region	The source region that you selected on the buy page. You cannot change the value of this parameter.
   	Instance ID	The ID of the source instance.
   	Database Password	The database password of the source instance. For information about the permissions that are required for the database account, see Permissions required for database accounts. Note The database password is in the <user>:<password> format. For example, if the username of the account that you use to log on to the instance is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
   Destination Instance Details	Instance Type	The type of the destination database. Select Redis Instance.
   	Instance Region	The destination region that you selected on the buy page. You cannot change the value of this parameter.
   	Instance ID	The ID of the destination instance.
   	Database Password	The database password of the destination instance. For information about the permissions that are required for the database account, see Permissions required for database accounts. Note The database password is in the <user>:<password> format. For example, if the username of the account that you use to log on to the instance is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.

7. In the lower-right corner of the page, click Set Whitelist and Next.

   Note

   • You do not need to modify the security settings for ApsaraDB instances, such as ApsaraDB RDS for MySQL and ApsaraDB for MongoDB, or self-managed databases that are hosted on Elastic Compute Service (ECS) instances. DTS automatically adds the CIDR blocks of DTS servers to the whitelists of ApsaraDB instances or the security group rules of ECS instances. For more information, see Add the CIDR blocks of DTS servers.

   • After data synchronization is complete, we recommend that you remove the CIDR blocks of DTS servers from the whitelists or security groups.

8. Select the processing mode of conflicting tables and the objects to be synchronized.

   Setting	Description
   Select the processing mode of conflicting tables	Pre-check and Intercept: checks whether the destination instance is empty. If the destination instance is empty, the precheck is passed. If the destination instance is not empty, an error is returned during the precheck and the data synchronization task cannot be started. Ignore: skips the check for empty destination instances. Warning If you select Ignore, data records in the source instance overwrite the data records that have the same keys in the destination instance. Proceed with caution.
   Select objects to be synchronized	Select one or more databases from the Available section and click the icon to move the database to the Selected section. You can select databases as the objects to be synchronized. Keys cannot be selected as the objects to be synchronized.
   Rename Databases and Tables	In this scenario, you cannot rename objects.
   Replicate Temporary Tables When DMS Performs DDL Operations	If you use DMS to perform online DDL operations on the source database, you can specify whether to synchronize temporary tables generated by online DDL operations. Yes: DTS synchronizes the data of temporary tables generated by online DDL operations. Note If online DDL operations generate a large amount of data, the data synchronization task may be delayed. No: DTS does not synchronize the data of temporary tables generated by online DDL operations. Only the original DDL data of the source database is synchronized. Note If you select No, the tables in the destination database may be locked.
   Retry Time for Failed Connections	By default, if DTS fails to connect to the source or destination database, DTS retries within the next 720 minutes (12 hours). You can specify the retry time based on your needs. If DTS reconnects to the source and destination databases within the specified time, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Note When DTS retries a connection, you are charged for the DTS instance. We recommend that you specify the retry time based on your business needs. You can also release the DTS instance at your earliest opportunity after the source and destination instances are released.

9. In the lower-right corner of the page, click Next.

10. Select the initial synchronization types. The value is set to Include full data + incremental data and cannot be modified.

    Note

    • DTS synchronizes historical data from the source instance to the destination instance. Then, DTS synchronizes incremental data.

    • If a version-related error message appears, you can upgrade the source instance to a specified version. For more information, see Upgrade the major version and Update the minor version of an instance.

11. In the lower-right corner of the page, click Precheck.

    Note

    • Before you can start the data synchronization task, DTS performs a precheck. You can start the data synchronization task only after the task passes the precheck.

    • If the task fails to pass the precheck, you can click the 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.

12. Close the Precheck dialog box after the The precheck is passed. message is displayed in the Precheck dialog box. Then, the data synchronization task starts.

13. Wait until the initial synchronization is complete and the data synchronization task enters the Synchronizing state.

    Note

    You can view the state of the data synchronization task on the Synchronization Tasks page.