one-way synchronization of Redis data across Alibaba Cloud accounts - Data Transmission Service

You can use Data Transmission Service (DTS) to perform one-way data synchronization between Tair (Redis OSS-Compatible) instances that belong to different Alibaba Cloud accounts. This feature is suitable for scenarios such as resource migration or merging across Alibaba Cloud accounts and business architecture adjustment.

Prerequisites

The destination Tair (Redis OSS-Compatible) instance is created. The available storage space of this instance is larger than the total size of data in the source instance.

Note

For more information about the supported instance versions, see Overview of data synchronization scenarios.

Background

In this example, two Tair (Redis OSS-Compatible) instances are created by different Alibaba Cloud accounts. You want to synchronize data from the Tair (Redis OSS-Compatible) instance of Account A to the Tair (Redis OSS-Compatible) instance of Account B.

You must perform the steps described in the following table to configure a data synchronization task.

Step	Description
1. Use Account A that owns the source instance to log on to the Resource Access Management (RAM) console and grant the required permissions to a RAM role. For more information, see the Preparations section of this topic.	When you configure the RAM role, set Account B as the trusted account and authorize the RAM role to access the cloud resources of Account A.
2. Use Account B that owns the destination instance to log on to the DTS console and configure the data synchronization task. For more information, see the Procedure section of this topic.	DTS can read the information about the source Tair (Redis OSS-Compatible) instance across Alibaba Cloud accounts.

Notes

Category	Description
Limits on the source database	To ensure the synchronization quality, Data Transmission Service (DTS) adds a key prefixed with DTS_REDIS_TIMESTAMP_HEARTBEAT to the source database. This key is used to record the time when data is synchronized to the destination database. If the source database is deployed in a cluster architecture, DTS adds this key to each shard. The key is filtered out during data synchronization. After the data synchronization task is complete, the key expires. If the source database is a read-only database or the source database account that is used to run the data synchronization task does not have the permissions to run the SETEX command, the reported latency may be inaccurate. 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. If an expiration policy is enabled for specific keys in the source database, these keys may not be deleted in a timely manner after they expire. Therefore, the number of keys in the destination database may be smaller than that in the source database. You can run the info command to view the number of keys in the destination database. Limits on synchronizing data from a standalone Tair (Redis OSS-Compatible) instance to an Tair (Redis OSS-Compatible) cluster instance: Each command can be run only on a single slot in an Tair (Redis OSS-Compatible) 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 source database is a Tair cloud-native persistent memory-optimized instance, you must set the appendonly parameter to yes for the instance.
Other limits	The timeout period for data replication between the master and replica nodes in the source database is specified by the repl-timeout parameter. If the source database is a self-managed Redis database, we recommend that you run the `config set repl-timeout 600` command to set this timeout period to 600 seconds. If the source database contains a large amount of data, you can increase the value of the repl-timeout parameter based on your business requirements. During data synchronization, if the number of shards in the source Redis database is increased or decreased, or if you change the database specifications, such as scaling up the memory capacity, 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 Redis database before you reconfigure the task. If the source or destination database is a self-managed Redis database and the endpoint of the self-managed Redis database is changed during data synchronization, you must reconfigure the data synchronization task. To ensure compatibility, the version of the destination database must be the same as or later than that of the source database. If the version of the destination database is earlier than that of the source database, database compatibility issues may occur. During initial full data synchronization, DTS uses read and write resources of the source and destination databases. This may increase the loads on the database servers. Before you run a task to 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. Data inconsistency between the source and destination databases may occur if data from other sources is written to the destination database during data synchronization. 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). By default, the maxmemory-policy parameter that specifies how data is evicted is set to volatile-lru for Tair (Redis OSS-compatible) 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 Tair? If the transparent data encryption (TDE) feature is enabled for the source or destination database, you cannot use DTS to synchronize data. During data synchronization, if resumable upload fails due to transient connections that occur on the source Redis database, full data may be re-synchronized to the destination database. This may cause data inconsistency between the source and destination databases. If Transport Layer Security (TLS) encryption is enabled for the source or destination Tair (Redis OSS-Compatible) instance, you must select SSL-encrypted for the instance when you configure the DTS task. TLSv1.3 is not supported. If SSL encryption is enabled for the source or destination Tair (Redis OSS-Compatible) instance, you cannot set Access Method to Alibaba Cloud Instance for the instance.

Billing

Synchronization type	Task configuration fee
Schema synchronization and full data synchronization	Free of charge.
Incremental data synchronization	Charged. For more information, see Billing overview.

Commands that can be incrementally synchronized

Edition	Command
Tair (Redis OSS-compatible) Community Edition	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, UNLINK (These two commands can be synchronized only if the engine version of the source database is Redis 4.0.) XADD, XCLAIM, XDEL, XAUTOCLAIM, XGROUP CREATECONSUMER, and XTRIM
Tair (Redis OSS-compatible) Enterprise Edition	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, RPOP, RPOPLPUSH, RPUSH, and RPUSHX SADD, SDIFFSTORE, SELECT, SET, SETBIT, SETEX, SETNX, SETRANGE, SINTERSTORE, SMOVE, SPOP, SREM, and SUNIONSTORE UNLINK, ZADD, ZINCRBY, ZINTERSTORE, ZREM, ZREMRANGEBYLEX, ZUNIONSTORE, ZREMRANGEBYRANK, and ZREMRANGEBYSCORE XADD, XCLAIM, XDEL, XAUTOCLAIM, XGROUP CREATECONSUMER, and XTRIM

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.

Preparations

Use the Alibaba Cloud account that owns the source Tair (Redis OSS-Compatible) instance to log on to the Alibaba Cloud Management console. Create a RAM role and set the Alibaba Cloud account that owns the destination Redis instance as the trusted account. For more information, see Configure RAM authorization for cross-account DTS tasks.

Procedure

Use the Alibaba Cloud account that owns the destination Tair (Redis OSS-Compatible) instance to go to the Data Synchronization Tasks page in one of the following two ways.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Synchronization.
3. In the upper-left corner of the page, select the region in which the data synchronization instance resides.
DMS console
Note
The actual operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Customize the layout and style of the DMS console.
1. Log on to the DMS console.
2. In the top navigation bar, move the pointer over Data Development and choose DTS (DTS) > Data Synchronization.
3. From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.
Optional. Click New Configuration Page in the upper-right corner of the page.
Note
- Skip this step if the Back to Previous Version button is displayed in the upper-right corner of the page.
- Specific parameters in the new and previous versions of the configuration page may be different. We recommend that you use the new version of the configuration page.

Configure the source and destination databases. The following table describes the parameters.

Warning

After you configure the source and destination databases, we recommend that you read the Limits that are displayed on the page. Otherwise, the task may fail or data inconsistency may occur.

Section	Parameter	Description
N/A	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify a descriptive name that makes it easy to identify the task. You do not need to specify a unique task name.
Source Database	Select Existing Connection	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information. Note In the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections. In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
	Database Type	Select Tair/Redis.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region to which the source apsaradb for Tair (compatible with Redis) instance belongs.
	Replicate Data Across Alibaba Cloud Accounts	Select Yes. Note This feature supports cross-site communication, allowing communication between China site accounts and international site accounts.
	Alibaba Cloud Account	Enter the ID of the Alibaba Cloud account (primary account) to which the source apsaradb for Tair (compatible with Redis) instance belongs.
	RAM Role Name	Enter the name of the RAM role created in Preparations.
	Instance ID	Select the ID of the source apsaradb for Tair (compatible with Redis) instance.
	Authentication Method	Select this parameter based on your business requirements. Password Login is selected in this example. Note If the Secret-free login is selected, make sure that password-free access over an ApsaraDB for Redis instance is enabled. For more information about how to enable password-free access over a Tair (Redis OSS-compatible)instance, see Enable password-free access.
	Database Password	Enter the account and password of the source apsaradb for Tair (compatible with Redis). Enter the password based on the selected account (which must have read permission). If you forget the password, you can reset it. For more information, see Modify or reset the password. If you use the default account whose username is the same as the instance ID, directly enter the password. For a newly created account, the password format is `<custom account>:<password>`, for example: testaccount:Test1234. Note This field is optional. If no password is set, you can leave it blank.
	Encryption	Specifies whether to encrypt the connection to the source database. Select Non-encrypted or SSL-encrypted based on your business requirements. If the SSL encryption feature is disabled for the source self-managed Redis instance, select Non-encrypted. If the SSL encryption feature is enabled for the source self-managed Redis database, select SSL-encrypted. In this case, you must upload a CA Certificate and configure the CA Key parameter.
Destination Database	Select Existing Connection	The database that you want to use. You can choose whether to use an existing database based on your business requirements. If you select an existing database, DTS automatically populates the parameters for the database. If you do not select an existing database, you must configure the following database information. Note In the DTS console, register a database with DTS on the Database Connections page or the new configuration page. For more information, see Manage database connections. In the DMS console, you can select an existing database from the Select a DMS database instance. drop-down list. You can also click Add DMS Database Instance or go back to the homepage of the DMS console to register a database with DMS. For more information, see Register an Alibaba Cloud database instance and Register a database hosted on a third-party cloud service or a self-managed database.
	Database Type	Select Tair/Redis.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	Select the region to which the destination apsaradb for Tair (compatible with Redis) instance belongs.
	Replicate Data Across Alibaba Cloud Accounts	This example is a cross-account synchronization instance at the source end. Select No here.
	Instance ID	Select the ID of the destination apsaradb for Tair (compatible with Redis) instance.
	Authentication Method	Select this parameter based on your business requirements. Password Login is selected in this example. Note If the Secret-free login is selected, make sure that password-free access over an ApsaraDB for Redis instance is enabled. For more information about how to enable password-free access over a Tair (Redis OSS-compatible) instance, see Enable password-free access.
	Database Password	Enter the account and password of the destination apsaradb for Tair (compatible with Redis) instance. Enter the password based on the selected account (which must have read and write permissions). If you forget the password, you can reset it. For more information, see Modify or reset the password. If you use the default account whose username is the same as the instance ID, directly enter the password. For a newly created account, the password format is `<custom account>:<password>`, for example: testaccount:Test1234.
	Encryption	Specifies whether to encrypt the connection to the source database. Select Non-encrypted or SSL-encrypted based on your business requirements. If the SSL encryption feature is disabled for the source self-managed Redis instance, select Non-encrypted. If the SSL encryption feature is enabled for the source self-managed Redis database, select SSL-encrypted. In this case, you must upload a CA Certificate and configure the CA Key parameter.

Click Test Connectivity and Proceed in the lower part of the page.
Note
- Make sure that the CIDR blocks of DTS servers can be automatically or manually added to the security settings of the source and destination databases to allow access from DTS servers. For more information, see Add the CIDR blocks of DTS servers.
- If the source or destination database is a self-managed database and its Access Method is not set to Alibaba Cloud Instance, click Test Connectivity in the CIDR Blocks of DTS Servers dialog box.

Configure the objects to be synchronized.

In the Configure Objects step, configure the objects that you want to synchronize.

Parameter	Description
Synchronization Types	By default, Incremental Data Synchronization or Full Data Synchronization and Incremental Data Synchronization is selected. If you select the Incremental Data Synchronization for a DTS instance, we recommend that you select Full Data Synchronization at the same time. After the precheck is complete, DTS synchronizes the historical data of selected objects from the source instance to the destination instance. The historical data serves as the basis for subsequent incremental synchronization.
Synchronization Topology	Select One-way Synchronization. Note This parameter is available only if both the source and destination instances are Tair (Enterprise Edition) instances.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether data exists in the destination database. If no data exists in the destination database, the precheck is passed. If data exists in the destination database, an error is returned during the precheck, and the data synchronization task cannot be started. Ignore Errors and Proceed: skips the Check the existence of objects in the destination database. check item. Warning If you select Ignore Errors and Proceed, data loss may occur in the destination database because data records in the source database overwrite the data records that have the same keys in the destination database. Proceed with caution.
Source Objects	Select one or more objects from the Source Objects section and click the icon to add the objects to the Selected Objects section. Note You can select only databases as the objects to be synchronized. You cannot select keys as the objects to be synchronized.
Selected Objects	If you want to select a database to which data is synchronized from DB 0 to DB 255 or filter the data to be synchronized by prefix, you can use the object name mapping feature or the filtering feature. In the Selected Objects section, right-click the database that you want to synchronize. In the Edit Schema dialog box, configure the parameters. For more information, see Map object names and Specify filter conditions. Note You cannot map multiple object names at a time.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Dedicated Cluster for Task Scheduling	By default, DTS schedules the task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data synchronization tasks, purchase a dedicated cluster. For more information, see What is a DTS dedicated cluster.
Retry Time for Failed Connections	The retry time range for failed connections. If the source or destination database fails to be connected after the data synchronization task is started, DTS immediately retries a connection within the time range. Valid values: 10 to 1440. Unit: minutes. Default value: 720. We recommend that you set this 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 synchronization task. Otherwise, the data synchronization task fails. Note If you specify different retry time ranges for multiple data synchronization tasks that have the same source or destination database, the shortest retry time range 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.
Retry Time for Other Issues	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data synchronization task is started, DTS immediately retries the operations within the time range. Valid values: 1 to 1440. Unit: minutes. Default value: 10. We recommend that you set this parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data synchronization task. Otherwise, the data synchronization task fails. Important The value of the Retry Time for Other Issues parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Full Data Migration	During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the load on the database servers. You can configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and Data migration speed for full migration (MB/s) parameters for full data synchronization tasks to reduce the load on the destination database server. Note You can configure this parameter only if you select Full Data Synchronization for the Synchronization Types parameter.
Enable Throttling for Incremental Data Synchronization	Specifies whether to enable throttling for incremental data synchronization. You can enable throttling for incremental data synchronization based on your business requirements. To configure throttling, you must configure the RPS of Incremental Data Synchronization and Data synchronization speed for incremental synchronization (MB/s) parameters. This reduces the load on the destination database server.
Extend Expiration Time of Destination Database Key	The extended time period for keys synchronized 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 this parameter to ensure data consistency. Note If the extended time period is specified in a scenario that provides you with distributed lock service, you may fail to release the distributed lock in a timely manner. `EXPIRE key seconds PEXPIRE key milliseconds EXPIREAT key timestamp PEXPIREAT key timestampMs`
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements. In this example, no environment tag is selected.
Configure ETL	Specifies whether to enable the extract, transform, and load (ETL) feature. For more information, see What is ETL? Valid values: Yes: configures the ETL feature. You can enter data processing statements in the code editor. For more information, see Configure ETL in a data migration or data synchronization task. No: does not configure the ETL feature.
Monitoring and Alerting	Specifies whether to configure alerting for the data synchronization task. If the task fails or the synchronization latency exceeds the specified threshold, alert contacts will receive notifications. Valid values: No: does not enable alerting. Yes: configures alerting. In this case, you must also configure the alert threshold and alert notification settings. For more information, see the "Configure monitoring and alerting when you create a DTS task" section of the Configure monitoring and alerting topic.

Click Next Step: Data Verification to configure data verification.
For more information about how to use the data verification feature, see Configure a data verification task.

Save the task settings and run a precheck.
- To view the parameters to be specified when you call the relevant API operation to configure the DTS task, move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters.
- If you do not need to view or have viewed the parameters, click Next: Save Task Settings and Precheck in the lower part of the page.
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 data synchronization task fails the precheck, click View Details next to each failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, rerun the precheck.
- If an alert is triggered for an item during the precheck:
  If an alert item cannot be ignored, click View Details next to the failed item and troubleshoot the issue. Then, run a precheck again.
  If an alert item can be ignored, click Confirm Alert Details. In the View Details dialog box, click Ignore. In the message that appears, click OK. Then, click Precheck Again to run a precheck again. If you ignore the alert item, data inconsistency may occur, and your business may be exposed to potential risks.

Purchase an instance.

Wait until the Success Rate becomes 100%. Then, click Next: Purchase Instance.

On the buy page, configure the Billing Method and Instance Class parameters for the data synchronization instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Billing Method	Subscription: You pay for a subscription when you create a data synchronization instance. The subscription billing method is more cost-effective than the pay-as-you-go billing method for long-term use. Pay-as-you-go: A pay-as-you-go instance is billed on an hourly basis. The pay-as-you-go billing method is suitable for short-term use. If you no longer require a pay-as-you-go data synchronization instance, you can release the instance to reduce costs.
	Resource Group Settings	The resource group to which the data synchronization instance belongs. Default value: default resource group. For more information, see What is Resource Management?
	Instance Class	DTS provides instance classes that vary in synchronization speed. You can select an instance class based on your business requirements. For more information, see Instance classes of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, specify the subscription duration and the number of data synchronization instances that you want to create. The subscription duration can be one to nine months, one year, two years, three years, or five years. Note This parameter is available only if you select the Subscription billing method.

Read and select Data Transmission Service (Pay-as-you-go) Service Terms.
Click Purchase and Start. In the dialog box that appears, click OK.
You can view the progress of the task on the Data Synchronization page.
Note
If a DTS instance you configured supports both full data synchronization and incremental data synchronization tasks, that is, the Synchronization Types contains both Full Data Synchronization and Incremental Data Synchronization, Incremental Data Synchronization is displayed.