Data Transmission Service (DTS) supports one-way data synchronization between ApsaraDB for Redis instances. This feature is applicable to scenarios such as active geo-redundancy and geo-disaster recovery. This topic describes how to configure one-way data synchronization between ApsaraDB for Redis instances.

Note After you configure a data synchronization task, do not change the architecture type of the source and destination databases. For example, if you change the master-replica architecture to the cluster architecture, data synchronization fails. For more information, see the Architectures section in Overview.

Prerequisites

  • The database version of the source ApsaraDB for Redis instance is 4.0 or 5.0.
    Note The database version of the destination ApsaraDB for Redis instance can be 4.0 or 5.0. The version of the destination database must be the same as or later than the version of the source database. If you want to synchronize data between different versions of Redis databases, make sure that the versions of the source and destination databases are compatible. You can create a pay-as-you-go ApsaraDB for Redis instance to verify database compatibility. Then, you can release the instance or change the billing method to subscription.
  • 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.

Precautions

  • DTS uses resources of the source and destination databases during initial full data synchronization. This may increase the load of the database server. If you synchronize a large volume of data or 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 databases. We recommend that you synchronize data during off-peak hours.
  • If the database version of the source ApsaraDB for Redis instance is 2.8, incremental data synchronization is not supported.
  • We recommend that you do not run the FLUSHDB or FLUSHALL command in the source instance during data synchronization. Otherwise, data may become inconsistent between the source and destination instances.
  • If the data eviction policy (maxmemory-policy) of the destination instance is not set to noeviction, data may become inconsistent between the source and destination instances. For more information about the data eviction policy, see How does ApsaraDB for Redis evict data by default?

Supported synchronization topologies

  • One-way one-to-one synchronization
  • One-way one-to-many synchronization
  • One-way cascade synchronization

For more information about synchronization topologies, 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, PSETEX, and PUBLISH
  • RENAME, RENAME, 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 when the database version of the source ApsaraDB for Redis instance is 4.0)
Note
  • 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 synchronization, the destination database does not explicitly return the execution results of Lua scripts.
  • When DTS calls the SYNC or PSYNC command to transfer data of the LIST type, DTS does not clear the existing data. In this case, the destination database may contain duplicate data records.

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 Target Instance to Redis.
  2. Log on to the DTS console.
  3. In the left-side navigation pane, click Data Synchronization.
  4. At the top of the Synchronization Tasks page, select the region where the destination instance resides.Select a region
  5. Find the data synchronization instance and click Configure Synchronization Channel in the Actions column.
  6. Configure the source and destination instances.Configure the source and destination instances
    Section Parameter Description
    N/A Synchronization Task Name DTS automatically generates a task name. We recommend that you specify an informative name for easy identification. You do not need to use a unique task name.
    Source Instance Details Instance Type Select Redis Instance.
    Instance Region The region of the source instance. The region is the same as the source region that you selected when you purchased the data synchronization instance. You cannot change the value of this parameter.
    Instance ID Select the ID of the source ApsaraDB for Redis instance.
    Database Password Enter the database password of the source ApsaraDB for Redis instance.
    Note The format of the database password is <user>:<password>. For example, if the username of the custom account is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
    Destination Instance Details Instance Type Select Redis Instance.
    Instance Region The region of the destination instance. The region is the same as the destination region that you selected when you purchased the data synchronization instance. You cannot change the value of this parameter.
    Instance ID Select the ID of the destination ApsaraDB for Redis instance.
    Database Password Enter the database password of the destination ApsaraDB for Redis instance.
  7. In the lower-right corner of the page, click Set Whitelist and Next.
    Note DTS adds the CIDR blocks of DTS servers to the whitelists of the source and destination ApsaraDB for Redis instances. This ensures that DTS servers can connect to the source and destination ApsaraDB for Redis instances.
  8. Configure the processing mode in existing destination tables and the objects to be synchronized.Configure the processing mode and objects
    Parameter Description
    Processing Mode In Existed Target Table
    • Pre-check and Intercept: checks whether the destination database is empty. If the destination database is empty, the precheck is passed. If the database 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 databases.
      Warning If you select Ignore, the data records in the source database overwrite the data records that have the same keys in the destination database.
    Objects
    • Select one or more databases from the Available section and click the icon to move the databases to the Selected section.
    • You can select only databases as the objects to be synchronized. You cannot select keys as the objects to be synchronized.
  9. In the lower-right corner of the page, click Next.
  10. Configure initial synchronization. The value is set to Include full data + incremental data.
    Note DTS synchronizes both historical data and incremental data from the source ApsaraDB for Redis instance to the destination ApsaraDB for Redis instance.
    Configure initial synchronization for ApsaraDB for Redis instances
  11. In the lower-right corner of the page, click Precheck.
    Note
    • Before you can start the data synchronization task, a precheck is performed. You can start the data synchronization task only after the task passes the precheck.
    • If the task fails to pass the precheck, click the Info icon icon next to each failed item to view details. Troubleshoot the issues based on the causes and run the precheck again.
  12. Close the Precheck dialog box after the following message is displayed: The precheck is passed.
  13. Wait until the initial synchronization is complete and the data synchronization task is in the Synchronizing state.Status of the data synchronization task
    Note You can view the status of the data synchronization task on the Synchronization Tasks page.