Migrate data between Tair (Redis OSS-compatible) instances - Data Transmission Service

This topic describes how to migrate data between Tair (Redis OSS-compatible) instances by using Data Transmission Service (DTS).

Prerequisites

The source and destination Tair (Redis OSS-compatible) instances are created.
Note
- For more information about how to create an Tair (Redis OSS-compatible) instance, see Step 1: Create an instance.
- For more information about the supported database versions, see Overview of data migration scenarios.
The available storage space of the destination Tair (Redis OSS-compatible) instance is larger than the total size of the data in the source Tair (Redis OSS-compatible) instance.

Usage notes

Category	Description
Limits on the source database	Bandwidth requirements: The server on which the source database is deployed must have sufficient outbound bandwidth. Otherwise, the data migration speed decreases. The database version of the source Tair (Redis OSS-Compatible) instance cannot be 2.8. 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 data migration from a standalone Redis database to a Redis database deployed in the cluster architecture: Each command can be run only on a single slot in a Redis database deployed in the cluster architecture. 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. Otherwise, the migration task is 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. If the source is a Storage Medium of Persistent Memory Tair (Enterprise Edition) instance, ensure that the appendonly parameter value is set to `yes`. For more information, see procedure.
Other limits	A storage-optimized instance of Tair (Redis OSS-Compatible) Enhanced Edition cannot be configured as the source or destination database. 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 database 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 database to noeviction. If the memory of the destination database is insufficient, DTS fails to write data to the destination database and the migration task fails, but data of the destination database is not lost due to data eviction. Note For more information about data eviction policies, see How does Tair (Redis OSS-Compatible) evict data by default? If you call Lua scripts by running the EVAL or EVALSHA command, DTS cannot identify whether these Lua scripts are executed on the destination database. This is because the destination database 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. If an expiration policy is enabled for specific keys in the source database, these keys may not be immediately deleted 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 database. Note The number of keys that do not have the expiration policy enabled or have not expired is the same in 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 database. After full data migration is complete, the size of used tablespace of the destination database is larger than that of the source database. DTS attempts to resume the data migration task that failed within the last seven days. Before you switch workloads to the destination database, you must stop or release the failed tasks. You can also execute the `REVOKE` statement to revoke the write permissions from the accounts that are used by DTS to access the destination database. Otherwise, the data in the source database overwrites the data in the destination instance after the task is resumed. If both the source and destination databases are of Tair (Redis OSS-Compatible) instances, 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 the Transparent Data Encryption (TDE) feature is enabled for the destination database, you cannot use DTS to migrate data. If one of the following issues occurs during data migration, full data may be migrated to the destination database again. This may cause data inconsistency between the source and destination databases. The resumable upload fails due to transient connections that occur on the source or destination database. A primary/secondary switchover or failover occurs on the source or destination database. The endpoint of the source or destination database changes. If the ApsaraDB Tair (compatible with Redis) instance has enabled the TLS (Transport Layer Security) encryption feature, you must connect to DTS using SSL-encrypted (does not support TLSv1.3). Currently, it is not supported to connect an ApsaraDB Tair (compatible with Redis) instance with SSL enabled to DTS as an Alibaba Cloud Instance. If a data migration instance contains both full data and incremental data migration tasks, DTS may restart the full data and incremental data migration tasks after the instance is restarted. If a DTS task fails to run, DTS technical support will try to restore the task within 8 hours. During the restoration, the task may be restarted, and the parameters of the task may be modified. Note Only the parameters of the task may be modified. The parameters of databases are not modified. The parameters that may be modified include but are not limited to the parameters in the "Modify instance parameters" section of the Modify the parameters of a DTS instance topic.
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 data migration 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 excessively 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. If the Access Method of the self-managed Redis database is Public IP Address, you cannot specify Instance Mode to Cluster.

Billing

Migration type	Instance configuration fee	Internet traffic fee
Full data migration	Free of charge.	When the Access Method parameter of the destination database is set to Public IP Address, you are charged for Internet traffic. For more information, see Billing overview.
Incremental data migration	Charged. For more information, see Billing overview.

Migration types

Migration type	Description
Full data migration	DTS migrates the historical data of required 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 the 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
XADD, XCLAIM, XDEL, XAUTOCLAIM, XGROUP CREATECONSUMER, and XTRIM

Procedure

Use one of the following methods to go to the Data Migration page and select the region in which the data migration instance resides.
DTS console
1. Log on to the DTS console.
2. In the left-side navigation pane, click Data Migration.
3. In the upper-left corner of the page, select the region in which the data migration instance resides.
DMS console
Note
The actual operation 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 + AI > DTS (DTS) > Data Migration.
3. From the drop-down list to the right of Data Migration Tasks, select the region in which the data synchronization instance resides.
Click Create Task to go to the task configuration page.

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

Section	Parameter	Description
N/A	Task Name	The name of the DTS task. DTS automatically generates a task name. We recommend that you specify an informative name that makes it easy to identify the task. You do not need to specify a unique task name.
Task Name	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	The type of the source database. Select Tair/Redis.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source Tair (Redis OSS-compatible) instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
	Instance ID	The ID of the source Tair (Redis OSS-compatible) instance.
	Authentication Method	Select an authentication method based on your business requirements. In this example, select Password Login. Note Only Redis databases of version 6.0 or later support Account + Password Login. If you select Secret-free login, make sure that you enable the password-free access feature in the Redis database. For information about how to enable password-free access for a Tair (Redis OSS-Compatible) instance, see Enable password-free access.
	Database Password	The database password of the source Tair (Redis OSS-compatible) instance. The database account that corresponds to the password must have the 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 need to enter only the password. If you use a custom account, specify the password in the `<Custom account username>:<Password>` format. Example: testaccount:Test1234. Note This parameter is optional and can be left empty if no database password is set for the source Tair (Redis OSS-compatible) database.
	Encryption	Specifies whether to encrypt the connection to the source database. Select Non-encrypted or SSL-encrypted based on your business requirements. Note If you set Access Method is not to Alibaba Cloud Instance and select SSL-encrypted for the self-managed Redis database, you must upload a CA Certificate and enter a CA Key.
Task Name	Select Existing Connection	If you use a database instance that is registered with DTS, select the instance from the drop-down list. DTS automatically populates the following database parameters for the instance. For more information, see Manage database connections. Note In the DMS console, you can select the database instance from the Select a DMS database instance drop-down list. If you fail to register the instance with DTS, or you do not need to use the instance that is registered with DTS, you must configure the following database information.
	Database Type	The type of the destination database. Select Tair/Redis.
	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the destination Tair (Redis OSS-compatible) instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. Select No.
	Instance ID	The ID of the destination Tair (Redis OSS-compatible) instance.
	Authentication Method	Select an authentication method based on your business requirements. In this example, select Password Login. Note Only Redis databases of version 6.0 or later support Account + Password Login. If you select Secret-free login, make sure that you enable the password-free access feature in the Redis database. For information about how to enable password-free access for a Tair (Redis OSS-Compatible) instance, see Enable password-free access.
	Database Password	The database password of the destination Tair (Redis OSS-compatible) instance. The database account that corresponds to the password must have the 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 need to enter only the password. If you use a custom account, specify the password in the `<Custom account username>:<Password>` format. 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. Note If you set Access Method is not to Alibaba Cloud Instance and select SSL-encrypted for the self-managed Redis database, you must upload a CA Certificate and enter a CA Key.

In the lower part of the page, click Test Connectivity and Proceed.
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 migrated.

On the Configure Objects page, configure the objects that you want to migrate.

Parameter	Description
Migration Types	The migration type. Select Full Data Migration + Incremental Data Migration. If you do not have the permissions to run the SYNC or PSYNC command on the source database, select Full Data Migration.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination database is empty. If the destination database is empty, 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 Check the existence of objects in the destination database. check item. Warning If you select Ignore Errors and Proceed, the data in the source database overwrites the data in the destination database that has the same keys as the source data. This may cause data loss in the destination database. Proceed with caution.
Source Objects	Select one or more objects from the Source Objects section. Click the icon to add the objects to the Selected Objects section. Note You can select databases as the objects to be migrated. Keys cannot be selected as objects to be migrated.
Selected Objects	If you want to select a database to which data is migrated from DB 0 to DB 255 or filter the data to be migrated 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 migrate. In the Edit Schema dialog box, configure the parameters. For more information, see Map object names and Set 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 data migration task to the shared cluster if you do not specify a dedicated cluster. If you want to improve the stability of data migration 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 migration task is started, DTS immediately retries a connection within the retry time range. Valid values: 10 to 1,440. Unit: minutes. Default value: 720. We recommend that you set the parameter to a value greater than 30. If DTS is reconnected to the source and destination databases within the specified retry time range, DTS resumes the data migration task. Otherwise, the data migration task fails. Note If you specify different retry time ranges for multiple data migration tasks that share the same source or destination database, the value that is specified 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 requirements. You can also release the DTS instance at the earliest opportunity after the source database and destination instance are released.
Retry Time for Other Issues	The retry time range for other issues. For example, if DDL or DML operations fail to be performed after the data migration task is started, DTS immediately retries the operations within the retry 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 retry time range, DTS resumes the data migration task. Otherwise, the data migration 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	Specifies whether to enable throttling for full data migration. During full data migration, DTS uses the read and write resources of the source and destination databases. This may increase the loads of the database servers. You can enable throttling for full data migration based on your business requirements. To configure throttling, you must 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. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Full Data Migration for the Migration Types parameter.
Enable Throttling for Incremental Data Migration	Specifies whether to enable throttling for incremental data migration. To configure throttling, you must configure the RPS of Incremental Data Migration and Data migration speed for incremental migration (MB/s) parameters. This reduces the loads of the destination database server. Note You can configure this parameter only if you select Incremental Data Migration for the Migration Types parameter.
Extend Expiration Time of Destination Database Key	The extended time period for keys migrated from the source database to the destination database to remain valid. Unit: seconds. If specific commands such as the following commands are run, we recommend that you set the value of the parameter to ensure data consistency. Note In scenarios that involve distributed locks, the distributed locks may fail to be released in time. `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, you do not need to select an environment tag.
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 migration task. If the task fails or the migration latency exceeds the specified threshold, the alert contacts receive notifications. Valid values: No: does not configure 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 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 analyze the causes based on the check results, troubleshoot the issues. Then, 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 the 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 Purchase Instance page, configure the Instance Class parameter for the data migration instance. The following table describes the parameters.

Section	Parameter	Description
New Instance Class	Resource Group	The resource group to which the data migration instance belongs. Default value: default resource group. For more information, see What is Resource Management?
New Instance Class	Instance Class	DTS provides instance classes that vary in the migration speed. You can select an instance class based on your business scenario. For more information, see Instance classes of data migration instances.

Read and agree to Data Transmission Service (Pay-as-you-go) Service Terms by selecting the check box.
Click Buy and Start. In the message that appears, click OK.
You can view the progress of the task on the Data Migration page.
Note
If a DTS instance contains both full data and incremental data tasks (select Full Data Migration and Incremental Data Migration for Migration Types), Incremental Data Migration is displayed on the Data Migration page.