Migrate data from an ApsaraDB for Redis instance to another ApsaraDB for Redis instance across Alibaba Cloud accounts - Data Transmission Service

This topic describes how to migrate data from an ApsaraDB for Redis instance to another ApsaraDB for Redis instance across Alibaba Cloud accounts by using Data Transmission Service (DTS). DTS supports full data migration and incremental data migration. When you configure a data migration task, you can select both of the supported migration types to ensure service continuity.

Prerequisites

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.
If the source ApsaraDB for Redis instance is of the ApsaraDB for Redis Community Edition, the engine version is 4.0 or 5.0. If the source ApsaraDB for Redis instance is of the ApsaraDB for Redis Enhanced Edition (Tair), the engine version is 5.0.

Supported source and destination databases

The following table describes the supported types of Redis databases for which you can configure one-way data migration across Alibaba Cloud accounts.


Source database	Destination database
ApsaraDB for Redis instance Self-managed database hosted on Elastic Compute Service (ECS) Self-managed database connected over Express Connect, VPN Gateway, or Smart Access Gateway Self-managed database connected over CEN	ApsaraDB for Redis instance Self-managed database hosted on ECS Self-managed database connected over Express Connect, VPN Gateway, or Smart Access Gateway Self-managed database connected over CEN

Limits


Category	Migration description
Limits on the source database	Bandwidth requirements: The server to which the source database belongs must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. You must enable the data logging and append-only file (AOF) logging features for the source database. Limits on operations: If you perform only full data migration, do not write data to the source database during data migration. Otherwise, data may be inconsistent between the source and destination databases. To ensure data consistency, we recommend that you select full data migration and incremental data migration as the migration types. Limits on migrating data from a standalone Redis instance to a Redis cluster: Each command can be run only on a single slot in a Redis cluster. 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 migration. This prevents the data migration task from being interrupted. To ensure the stability of data migration, DTS inserts a key prefixed with DTS_REDIS_TIMESTAMP_HEARTBEAT into the source database to record when data is updated. If the source database is deployed in a cluster architecture, DTS inserts the key into each shard of the cluster. The key is filtered out during data migration. After the data migration 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 migration task does not have the permissions to run the SETEX command, the reported latency may be inaccurate.
Other limits	A storage-optimized instance of ApsaraDB for Redis Enhanced Edition (Tair) cannot be configured as the source or destination database. If the destination database is out of memory, data eviction is triggered. By default, the data eviction policy (maxmemory-policy) of an ApsaraDB for Redis instance is set to volatile-lru. Therefore, data inconsistency may occur between the source and destination databases. In this case, the data migration task can run as expected. To prevent data inconsistency between the source and destination databases, we recommend that you set the data eviction policy of the destination database to noeviction. If the destination database is out of memory, DTS fails to write data and the data migration task fails. However, data loss does not occur in the destination database due to data eviction. Note For more information about data eviction policies, see How does ApsaraDB for Redis evict data by default? If you run the EVAL or EVALSHA command to call Lua scripts, DTS cannot identify whether these Lua scripts are executed in the destination database. This is because the destination database does not explicitly return the execution results of Lua scripts during incremental data migration. When you run the `PSYNC` or `SYNC` command to transfer data of the LIST type, DTS does not perform the `FLUSH` operation on the existing data in the destination database. As a result, the destination database may contain duplicate data records. 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. To ensure compatibility, the version of the destination Redis database must be the same as or later than that of the source Redis database. Note If the version of the destination database is earlier than that of the source database, database compatibility issues may occur. Before you migrate data, evaluate the impact of data migration on the performance of the source and destination databases. We recommend that you migrate data during off-peak hours. During full data migration, DTS uses read and write resources of the source and destination databases. This may increase the loads of the database servers. During full data migration, concurrent INSERT operations cause fragmentation in the tables of the destination cluster. After full data migration is complete, the size of used tablespace of the destination cluster is larger than that of the source instance. DTS attempts to resume data migration tasks that failed within the last seven days. Before you switch workloads to the destination instance, stop or release the data migration task. You can also run the `REVOKE` command to revoke the write permissions from the accounts that are used by DTS to access the destination instance. Otherwise, the data in the source database overwrites the data in the destination database after the task is resumed. If both the source and destination databases are of ApsaraDB for Redis Community Edition or Enhanced Edition, take note of the following limits: If the database configurations are changed, such as the specifications or port number, DTS cannot obtain continuous log data or correct connection information. As a result, the data migration task is interrupted. To ensure data consistency, we recommend that you delete the data in the destination database and reconfigure the data migration task after the database configurations are changed. 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 Transparent Data Encryption (TDE) is enabled for the source or destination instance, you cannot use DTS to migrate data.
Special cases	If the source database is a self-managed Redis database, take note of the following limits: If you perform a primary/secondary switchover on the source database when the data migration task is running, the task fails. DTS calculates migration latency based on the timestamp of the latest migrated data in the destination database and the current timestamp in the source database. If no DML operation is performed on the source database for an extended period of time, the migration latency may be inaccurate. If the latency of the data migration task is too high, you can perform a DML operation on the source database to update the latency. Note If you select an entire database as the object to be migrated, you can create a heartbeat table. The heartbeat table is updated or receives data every second.

Migration types


Migration type	Description
Full data migration	DTS migrates the existing data of objects from the source database to the destination database.
Incremental data migration	After full data migration is complete, DTS migrates incremental data from the source database to the destination database. Incremental data migration allows data to be migrated smoothly without interrupting services of self-managed applications during data migration.

Commands that are supported for incremental data migration

APPEND
BITOP, BLPOP, BRPOP, and BRPOPLPUSH
DECR, DECRBY, and DEL
EVAL, EVALSHA, EXEC, EXPIRE, and EXPIREAT
FLUSHALL and FLUSHDB
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

Preparations

Use the Alibaba Cloud account that owns the source ApsaraDB for Redis instance to log on to the Alibaba Cloud Management Console. Then, create a RAM role and specify the Alibaba Cloud account that owns the destination ApsaraDB for Redis instance as a trusted account. For more information, see Configure RAM authorization for cross-account data migration or synchronization.

Procedure

Go to the Data Synchronization Tasks page.
1. Log on to the Data Management (DMS) console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
Note
- Operations may vary based on the mode and layout of the DMS console. For more information, see Simple mode and Configure the DMS console based on your business requirements.
- You can also go to the Data Synchronization Tasks page of the new DTS console.
From the drop-down list to the right of Data Synchronization Tasks, select the region in which the data synchronization instance resides.
Note If you use the new DTS console, you must select the region in which the data synchronization instance resides in the top navigation bar.

Click Create Task. On the page that appears, configure the source and destination databases.

Warning After you select the source and destination instances, we recommend that you read the limits displayed at the top of the page. This helps ensure that the task properly runs or prevent data inconsistency.


Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to specify a unique task name.
Source Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you use an existing instance, DTS automatically applies the parameter settings of the source database. If you do not use an existing instance, you must configure the parameters for the database.
	Database Type	Select Tair/Redis.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	The region where the source ApsaraDB for Redis instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether data is replicated across Alibaba Cloud accounts. In this example, Yes is selected.
	Alibaba Cloud Account	The ID of the Alibaba Cloud account that owns the source ApsaraDB for Redis instance. Note To obtain the ID of the Alibaba Cloud account that owns the source ApsaraDB for Redis instance, log on to the Account Management console by using this account. The account ID is displayed on the Basic Information page.
	RAM Role Name	The name of the RAM role that you created earlier in Preparations.
	Database Password	The database password of the source ApsaraDB for Redis instance. The database account that corresponds to the password must have read permissions. If you forget the password, you can reset the password. For more information, see Change or reset the password. If you use the default account whose username is the same as the instance ID, you can enter only the password. If you create a custom account, you must specify the password in the `<Custom account>:<Password>` format. Example: testaccount:Test1234. Note This parameter is optional and can be left empty if no database password is set.
Destination Database	Select an existing DMS database instance	The database instance that you want to use. You can choose whether to use an existing instance based on your business requirements. If you use an existing instance, DTS automatically applies the parameter settings of the instance. If you do not use an existing instance, you must configure the parameters for the database.
	Database Type	Select Tair/Redis.
	Access Method	Select Alibaba Cloud Instance.
	Instance Region	The region where the destination ApsaraDB for Redis instance resides.
	Instance ID	The ID of the destination ApsaraDB for Redis instance.
	Database Password	The database password of the destination ApsaraDB for Redis instance. The database account that corresponds to the password must have read permissions. If you forget the password, you can reset the password. For more information, see Change or reset the password. If you use the default account whose username is the same as the instance ID, you can enter only the password. If you create a custom account, you must specify the password in the `<Custom account>:<Password>` format. Example: testaccount:Test1234.

In the lower part of the page, click Test Connectivity and Proceed.
Warning If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of a database or an instance, or to the security group rules of an ECS instance, security risks may arise. Therefore, before you use DTS to migrate data, you must understand and acknowledge the potential risks and take preventive measures, including but not limited to the following measures: enhance the security of your username and password, limit the ports that are exposed, authenticate API calls, regularly check the whitelist or ECS security group rules and forbid unauthorized CIDR blocks, or connect the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.

Configure objects to migrate and advanced settings.

Basic Settings


Parameter	Description
Migration Type	To perform only full data migration, select only Full Data Migration. To ensure service continuity during data migration, select Full Data Migration and Incremental Data Migration. Note If Incremental Data Migration is not selected, we recommend that you do not write data to the source instance during data migration. This ensures data consistency between the source and destination instances. For more information, see Migration types.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database contains tables that have the same names as tables in the source database. If the source and destination databases do not contain identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Ignore Errors and Proceed: skips the precheck for identical table names in the source and destination databases. Warning If you select Ignore Errors and Proceed, data inconsistency may occur, and your business may be exposed to potential risks. If the source and destination databases have the same schema, DTS does not migrate data records that have the same primary keys as data records in the destination database. If the source and destination databases have different schemas, only some columns are migrated or the data migration task fails. Proceed with caution.
Select 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 migrated. Keys cannot be selected as objects to be migrated.
Rename Databases and Tables	The objects that you select to migrate. In this scenario, you cannot rename the objects.
Select the SQL operations to be migrated	In the Selected Objects section, right-click an object. In the dialog box that appears, select the commands that you want to migrate. For more information, see Commands that are supported for incremental data migration.

Advanced Settings


Parameter	Description
Set Alerts	Specifies whether to set alerts for the data migration task. If the task fails or the migration latency exceeds the threshold, the alert contacts will receive notifications. Valid values: No: does not set alerts. Yes: sets alerts. If you select Yes, you must also set the alert threshold and alert contacts. For more information, see Configure monitoring and alerting when you create a DTS task.
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 migration 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 the 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 migration task. Otherwise, the data migration task fails. Note If you set different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is set later takes precedence. If DTS retries a connection, you are charged for the operation of the DTS instance. We recommend that you specify the retry time based on your business needs and release the DTS instance at your earliest opportunity after the source and destination instances are released.
Configure ETL	Specifies whether to configure 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.

In the lower part of the page, click Next: Save Task Settings and Precheck.
Note
- Before you can start the data migration task, DTS performs a precheck. You can start the data migration task only after the task passes the precheck.
- If the task fails to pass the precheck, click View Details next to each failed item. After you troubleshoot the issues based on the causes, run a precheck again.
- 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 issues. 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.
Wait until the Success Rate value becomes 100%. Then, click Next: Purchase Instance.

On the Purchase Instance page, specify the Instance Class parameter for the data migration instance. The following table describes the parameter.


Section	Parameter	Description
Parameters	Instance Class	DTS provides several instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Specifications of data migration instances.

Read and select the check box to agree to Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.