Migrate data from a self-managed Redis database to a Tair instance - Data Transmission Service

This topic describes how to migrate data from a self-managed Redis database to a Tair instance by using Data Transmission Service (DTS). DTS supports full data migration and incremental data migration. When you migrate data from a self-managed Redis database to Alibaba Cloud, you can select the two migration types to ensure service continuity.

Prerequisites

A self-managed Redis database and a Tair instance are created. For more information about how to create the destination Tair instance, see Step 1: Create a Tair instance.
Note
- DTS supports only Tair instances for which the direct connection mode is enabled.
- DTS also allows you to migrate data from an ApsaraDB for Redis instance to a Tair instance or between Tair instances. You can refer to the instructions described in this topic to configure the migration task.
The engine version of the self-managed Redis database is 2.8, 3.0, 3.2, 4.0, 5.0, or 6.0.
The PSYNC or SYNC command can be run on the self-managed Redis database.
The available storage space of the destination Tair instance is larger than the total size of the data in the source self-managed Redis database.

Limits


Category	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) features for the source database. Limits on operations: If you perform only a 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 data migration from a standalone Redis database to a cluster instance: Each command can be run only on a single slot in a cluster instance. If you perform operations on multiple keys in the source database and the keys belong to different slots, an 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. If an expiration policy is enabled for specific keys in the source database, these keys may not be deleted immediately after they expire. Therefore, the number of keys in the destination instance may be less than that in the source database. You can run the INFO command to view the number of keys in the destination instance. 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 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	DTS consumes the resources of the source and destination databases during full data migration. This may increase the loads on the database servers. If you migrate a large volume of data or the server specifications cannot meet your requirements, database services may become unavailable. 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. If data eviction is triggered due to insufficient memory of the destination database, data inconsistency may occur between the source and destination databases. This is because the default data eviction policy (maxmemory-policy) of the destination Tair instance is volatile-lru. However, this does not affect the migration task. In this case, we recommend that you set the data eviction policy of the destination instance to noeviction. If the memory of the destination instance is insufficient, DTS fails to write data to the destination instance and the migration task fails, but data of the destination instance is not lost due to data eviction. Note For more information about data eviction policies, see How does ApsaraDB for Redis evict data by default? If Lua scripts are called by using the EVAL or EVALSHA command, 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 migration. When DTS runs 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 instance. As a result, the destination instance may contain duplicate data records. During data migration, if the number of shards in the self-managed 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 migration task. To ensure data consistency, we recommend that you delete the data that has been migrated to the destination Redis database before you reconfigure the data migration task. During data migration, if the endpoint of the self-managed Redis database is changed, you must reconfigure the data migration task. If a data migration task fails, DTS automatically resumes the task. Before you switch your workloads to the destination instance, stop or release the data migration task. This prevents the data in the source database from overwriting the data in the destination instance after the task is resumed. 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 in the destination instance, you cannot use DTS to migrate data.

Billing


Migration type	Task configuration fee	Internet traffic fee
Schema migration and full data migration	Free of charge.	Charged only when data is migrated from Alibaba Cloud over the Internet. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Full data migration
DTS migrates all the data of the objects to be migrated from the self-managed Redis database to the Tair instance.
Note If you perform only full data migration, we recommend that you do not write data to the self-managed Redis database during the full data migration. This ensures data consistency.
Incremental data migration
After a full data migration is complete, DTS migrates incremental data from the self-managed Redis database to the Tair instance. Incremental data migration allows data to be migrated smoothly without interrupting services of self-managed applications during data migration.

Commands that can be incrementally migrated

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 before incremental data migration

To ensure that the incremental data migration task runs as expected, we recommend that you remove the limit on the replication output buffer. In this topic, a server that runs on Linux is used in the example.

Note If you perform only full data migration, skip the following steps.

Use the redis-cli program to connect to the self-managed Redis database.
Note You can use the redis-cli program after you install the Redis client. For more information, visit Redis community official website.
```
redis-cli -h <host> -p <port> -a <password>
```
Note
- <host>: the endpoint that is used to connect to the self-managed Redis database. You can use 127.0.0.1 in this example.
- <port>: the service port number used to connect to the self-managed Redis database. The default port number is 6379.
- <password>: the password used to connect to the self-managed Redis database.
Example:
```
redis-cli -h 127.0.0.1 -p 6379 -a Test123456
```
Run the following command to remove the limit on the replication output buffer:
```
config set client-output-buffer-limit 'slave 0 0 0'
```

Procedure

Go to the Data Migration 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 Migration.
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 Migration Tasks page of the new DTS console.
From the drop-down list next to Data Migration Tasks, select the region in which the data migration instance resides.
Note If you use the new DTS console, you must select the region in which the data migration instance resides in the upper-left corner.

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


Section	Parameter	Description
N/A	Task Name	DTS automatically generates a task name. We recommend that you specify an informative name to identify the task. You do not need to use a unique task name.
Source Database	Select Instance	Select whether to use an existing instance. If you select an existing instance, DTS automatically applies the parameter settings of the instance. You do not need to configure the corresponding parameters again. If you do not use an existing instance, you must configure parameters for the source database.
	Database Type	The type of the source database. Select ApsaraDB for Redis Enhanced Edition (Tair).
	Access Method	The access method based on the deployment location of the source database. In this example, Self-managed Database on ECS is selected. Note If your source database is a self-managed database, you must deploy the network environment for the database. For more information, see Preparation overview.
	Instance Region	The region in which the source Redis database resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	ECS Instance ID	The ID of the Elastic Compute Service (ECS) instance that hosts the source Redis database. Note If the source Redis database is deployed in a cluster architecture, select the ID of the ECS instance on which a master node resides.
	Instance Mode	The architecture in which the source Redis database is deployed. Select Standalone or Cluster.
	Port Number	The service port number of the source Redis database. Default value: 6379. Note If the source Redis database is deployed in a cluster architecture, enter the service port number of a master node.
	Database Password	The password of the source Redis database. Note This parameter is optional and can be left empty if no password is set. The database password is in the <user>:<password> format. For example, if the username of the account that you use to log on to the source Redis database is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.
Destination Database	Select Instance	Select whether to use an existing instance. If you select an existing instance, DTS automatically applies the parameter settings of the instance. You do not need to configure the corresponding parameters again. If you do not use an existing instance, you must configure parameters for the source database.
	Database Type	The type of the destination instance. Select ApsaraDB for Redis Enhanced Edition (Tair).
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination Tair instance resides.
	Instance ID	The ID of the destination Tair instance.
	Database Password	The password of the destination Tair instance. Note The database password is in the <user>:<password> format. For example, if the username of the account that you use to log on to the destination Tair instance is admin and the password is Rp829dlwa, the database password is admin:Rp829dlwa.

In the lower part of the page for this step, click Test Connectivity and Proceed.
Warning
- If the source or destination database is an Alibaba Cloud database instance, such as an ApsaraDB RDS for MySQL or ApsaraDB for MongoDB instance, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the instance. If the source or destination database is a self-managed database hosted on an Elastic Compute Service (ECS) instance, DTS automatically adds the CIDR blocks of DTS servers to the security group rules of the ECS instance. For more information, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases. If the source or destination database is a self-managed database that is deployed in a data center or provided by a third-party cloud service provider, you must manually add the CIDR blocks of DTS servers to the whitelist of the database to allow DTS to access the database.
- If the CIDR blocks of DTS servers are automatically or manually added to the whitelist of the database, Alibaba Cloud database instance, or ECS security group rules, 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: enhancing the security of your username and password, limiting the ports that are exposed, authenticating API calls, regularly checking the whitelist or ECS security group rules and forbidding unauthorized CIDR blocks, or connecting the database to DTS by using Express Connect, VPN Gateway, or Smart Access Gateway.
- After the DTS task is complete or released, we recommend that you manually detect and remove the added CIDR blocks from the whitelist or ECS security group rules.

Select objects for the task and configure advanced settings.


Parameter	Description
Migration Types	The migration type. Select Full Data Migration + Incremental Data Migration.
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.
Use Slave Node	If the Instance Mode parameter of the source self-managed Redis database is set to Cluster, you can pull data from the master or slave nodes.
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 migrate. Keys cannot be selected as objects to migrate.
Selected Objects	The objects that you select to migrate. In this scenario, you cannot rename the objects.

Click Next: Advanced Settings to configure advanced settings.

Data Verification Settings
For more information about how to enable data verification, see Enable data verification.

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 Connection	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: 120. 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. 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 needs. You can also release the DTS instance at your earliest opportunity after the source database and destination instances are released.
The wait time before a retry when other issues occur in the source and destination databases.	The retry time range for other issues. For example, if the DDL or DML operations fail to be performed after the data migration 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 the parameter to a value greater than 10. If the failed operations are successfully performed within the specified time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Important The value of the The wait time before a retry when other issues occur in the source and destination databases parameter must be smaller than the value of the Retry Time for Failed Connections parameter.
Enable Throttling for Incremental Data Migration	The load on the destination instance may increase when DTS migrates incremental data to the destination instance. You can configure throttling thresholds for the number of rows and the amount of data that can be incrementally migrated per second based on your business requirements. This helps reduce the load on the destination instance.
Extend Expiration Time of Destination Database Key	The extended time period for keys migrated 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 the parameter to 600 to ensure data consistency: `EXPIRE key seconds PEXPIRE key milliseconds EXPIREAT key timestamp PEXPIREAT key timestampMs`
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 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 for 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.