ApsaraDB for Redis is a database service that is compatible with the open source Redis protocol and supports a hybrid of memory and disks for storage. Based on reliable hot standby architectures and scalable cluster architectures, ApsaraDB for Redis is suitable for scenarios that require flexible configuration changes, high throughput, and low latency. This topic describes how to synchronize data from a Twemproxy Redis cluster to an ApsaraDB for Redis instance by using Data Transmission Service (DTS).

Prerequisites

  • An ApsaraDB for Redis instance is created. For more information, see Step 1: Create an ApsaraDB for Redis instance.
  • The available storage capacity of the ApsaraDB for Redis instance is larger than the total size of data stored in the Twemproxy Redis cluster.
  • All master nodes in the Twemproxy Redis cluster support the PSYNC command.

How DTS synchronizes data from a Twemproxy Redis cluster

A Twemproxy Redis cluster consists of multiple Redis servers. DTS synchronizes data of each Redis server in a data synchronization task until the entire cluster is synchronized.

Synchronize data from a Twemproxy Redis cluster

Architecture of the Twemproxy Redis cluster

In this topic, the Twemproxy Redis cluster consists of two Redis servers. Each Redis server runs in a master-replica architecture. The following figure shows the architecture of the cluster.

Architecture of a Twemproxy Redis cluster

Usage notes

  • DTS uses the resources of the source and destination instances during initial full data synchronization. This may increase the loads of the database servers. If you migrate a large amount 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 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.
  • To ensure the stability of data synchronization, we recommend that you increase the value of the repl-backlog-size parameter in the redis.conf file of the source Codis cluster.
  • To ensure the synchronization quality, DTS adds the following key to the source Codis cluster: 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 Codis cluster. Otherwise, data may become inconsistent between the source and destination databases.
  • If the data eviction policy (maxmemory-policy) of the destination instance is not set to noeviction, data inconsistency may occur between the source and destination instances. For more information about data eviction policies, see How does ApsaraDB for Redis evict data by default?
  • 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.
  • The database version of the destination ApsaraDB for Redis instance must be 2.8, 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 with each other. For example, you can create a destination pay-as-you-go ApsaraDB for Redis instance to verify the compatibility between the source and destination databases. Then, you can release the instance or change the billing method of the instance to subscription.

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.

SQL 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
Note
  • PUBLISH operations cannot be synchronized.
  • If you run the EVAL or EVALSHA command to call Lua scripts, DTS cannot identify whether these Lua scripts are executed on the destination instance. This is because the destination instance does not explicitly return the execution results of Lua scripts during incremental data synchronization.
  • When DTS runs the SYNC or PSYNC command to transfer data of the LIST type, DTS does not clear the existing data in the destination instance. As a result, the destination instance may contain duplicate data records.

Procedure

  1. Purchase a data synchronization instance. For more information, see Purchase a DTS instance.
    Note On the buy page, select Redis as both the source and destination instance type and One-way Synchronization as the synchronization topology.
  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.
  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 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 Select User-Created Database in ECS Instance.
    Instance Region The source region that you selected on the buy page. You cannot change the value of this parameter.
    ECS Instance ID The ID of the Elastic Compute Service (ECS) instance that hosts the master node of the Redis-Server.
    Note DTS synchronizes each Redis server of the Twemproxy Redis cluster by using a data synchronization task until the entire cluster is synchronized. In this step, enter the ECS instance ID for the master node of the Redis server 1. When you configure the data synchronization task for the Redis server 2, enter the ECS instance ID for the master node of the Redis server 2. You can configure data synchronization tasks for all Redis servers by following the procedure described in this topic.
    Database Type The value of this parameter is fixed to Redis.
    Instance Mode Select Standalone.
    Note You must select Standalone for this parameter because data from a Twemproxy Redis cluster cannot be synchronized at a time. DTS synchronizes data of each Redis server of the cluster in a data synchronization task until all Redis servers are synchronized.
    Port Number The service port number of the master node in the Redis-Server.
    Database Password The database password of the master node.
    Note This parameter is optional and can be left empty if no database password is set.
    Destination Instance Details Instance Type Select Redis Instance.
    Instance Region The destination region that you selected on the buy page. You cannot change the value of this parameter.
    Redis Instance ID The ID of the destination ApsaraDB for Redis instance.
    Database Password The database password of the ApsaraDB for Redis instance.
    Note The database password is in the <user>:<password> format. For example, if the username of a custom account 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) and ECS-hosted databases. DTS automatically adds the CIDR blocks of DTS servers to the whitelists of ApsaraDB instances or the security group rules of Elastic Compute Service (ECS) instances. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
    • 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.
    Select objects to be synchronized
    Setting Description
    Select the processing mode of conflicting tables DTS synchronizes each Redis server of the Twemproxy Redis cluster in a data synchronization task until the entire cluster is synchronized. When you configure data synchronization for the Redis server 1, select Pre-check and Intercept if the ApsaraDB for Redis instance has no data. When you configure data synchronization for the Redis server 2 to N, select Ignore. Otherwise, errors may occur during data synchronization.
    Note
    • 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 precheck for empty destination databases and continues with data synchronization. If the keys in the destination database are the same as those in the source database during data synchronization, the keys in the source database overwrite those in the destination database.
    Select the objects to be synchronized
    • Select one or more databases from the Available section and click to add the databases to the Selected section.
    • You can select only databases as the objects to be synchronized. Keys cannot be selected as the objects to be synchronized.
    Rename Databases and Tables The objects that you select to synchronize. In this scenario, you cannot rename the objects.
    Replicate Temporary Tables When DMS Performs DDL Operations
    If you use Data Management (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. Configure initial synchronization.
    Configure initial synchronization
    Note The value is set to Include full data + incremental data. DTS synchronizes historical data from the source Twemproxy Redis cluster to the destination Redis database and then synchronizes incremental data.
  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.
      • After you troubleshoot the issues based on the causes, you can 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 following message is displayed: The precheck is passed. Then, the data synchronization task starts.
  13. Wait until initial synchronization is complete and the data synchronization task enters the Synchronizing state.
    Synchronizing
    Note You can view the status of the data synchronization task on the Synchronization Tasks page.
  14. Create and configure a data synchronization task for every other Redis server by repeating Step 1 to 13.

Result

In this topic, the Twemproxy Redis cluster consists of two Redis servers. You must create two data synchronization tasks. The following figure shows that the initial synchronization is complete for both tasks and both tasks are in the Synchronizing state.

Synchronizing the Twemproxy Redis cluster

In this topic, the database DB0 is synchronized. You can use Data Management (DMS) to log on to the destination ApsaraDB for Redis instance and check the total number of keys in the instance. The total number of keys is the same as that in the Twemproxy Redis cluster. For more information about DMS usage, see Log on to an ApsaraDB for Redis instance by using DMS.

Figure 1. ApsaraDB for Redis instance
Total number of keys in the ApsaraDB for Redis instance
Figure 2. Source Twemproxy Redis cluster
Total number of keys in the Twemproxy Redis cluster