Data Transmission Service (DTS) supports one-way data synchronization between two Redis databases. This feature is applicable to scenarios such as active geo-redundancy and geo-disaster recovery. This topic describes how to synchronize data from a user-created Redis database connected over Express Connect, VPN Gateway, or Smart Access Gateway to a user-created Redis database hosted on ECS.

Warning After you configure a data synchronization task, do not change the architecture type of the source or destination database. For example, if you change the master-replica architecture to the cluster architecture, data synchronization fails.

Prerequisites

  • The version of the source Redis database is 2.8, 3.0, 3.2, 4.0, or 5.0.
    Note The version of the destination Redis database can be 2.8, 3.0, 3.2, 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 synchronize data between different versions of Redis databases, make sure that the versions of the source and destination databases are compatible.
  • The available storage space of the destination Redis database is larger than the total size of the data in the source Redis database.
  • If the source Redis database is deployed in a cluster architecture, all nodes of the Redis cluster must support the PSYNC command and share the same password.

Precautions

  • DTS uses the resources of the source and destination databases during initial full data synchronization. This may increase the loads of the database servers. 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 an expiration policy is enabled for some keys in the source database, some 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.
  • If the bind parameter is configured in the redis.conf file of the source database, you must set the value of this parameter to the internal IP address of the ECS instance. The setting ensures that DTS can connect to the source database.
  • We recommend that you increase the value of the repl-backlog-size parameter in the redis.conf file of the source Redis database. This ensures the stability of data synchronization.
  • To ensure the synchronization quality, DTS adds the following key to the source Redis database: DTS_REDIS_TIMESTAMP_HEARTBEAT. This key is used to record the time when data is synchronized to ApsaraDB for Redis.
  • We recommend that you do not run the FLUSHDB or FLUSHALL command in the source database during data synchronization. Otherwise, data may become inconsistent between 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. For more information about data eviction policies, 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, 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 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 User-Created Database Connected over Express Connect, VPN Gateway, or Smart Access Gateway.
    Instance Region The source region that you selected on the buy page. You cannot change the value of this parameter.
    Peer VPC Select the ID of the VPC that is connected to the source Redis database.
    Database Type The value of this parameter is set to Redis.
    Instance Mode Select Standalone or Cluster based on the architecture of the source Redis database.
    IP Address Enter the server IP address of the source Redis database.
    Note If the source Redis database is deployed in a cluster architecture, enter the IP address of the server to which a master node belongs.
    Port Number Enter the service port number of the source Redis database. The default port number is 6379.
    Note If the source Redis database is deployed in a cluster architecture, enter the service port number of a master node.
    Database Password Enter the password of the source Redis database.
    Note This parameter is optional and can be left blank if no database password is set.
    Destination Instance Details Instance Type Select User-Created Database in ECS Instance.
    Instance Region The destination region that you selected on the buy page. You cannot change the value of this parameter.
    Instance ID Select the ID of the ECS instance that is connected to the destination Redis database.
    Note If the destination Redis database is deployed in a cluster architecture, select the ID of the ECS instance where a master node resides.
    Instance Mode Select Standalone or Cluster based on the architecture of the destination Redis database.
    Port Number Enter the service port number of the destination Redis database. The default port number is 6379.
    Note If the destination Redis database is deployed in a cluster architecture, enter the service port number of a master node.
    Database Password Enter the password of the destination Redis database.
    Note This parameter is optional and can be left blank if no database password is set.
  7. In the lower-right corner of the page, click Set Whitelist and Next.
    Note DTS adds the CIDR blocks of DTS servers to an inbound rule of the destination ECS instance. This ensures that DTS servers can connect to the destination ECS instance.
  8. Select the processing mode of conflicting tables, and the objects to be synchronized.Select the processing mode and objects
    Setting Description
    Select the processing mode of conflicting tables
    • 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 database.
      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.
    Select the objects to be synchronized
    • 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. Configure initial synchronization
    Note
    • DTS synchronizes historical data from the source ApsaraDB for Redis instance to the destination ApsaraDB for Redis instance. Then, DTS synchronizes incremental data.
    • If a version-related error message appears, you can upgrade the source ApsaraDB for Redis instance to a specified version. For more information, see Upgrade the major version and Upgrade the minor version.
  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 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.
  12. Close the Precheck dialog box after the following message appears: The precheck is passed. Then, the data synchronization task starts.
  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.