Data Transmission Service：Migrate data from a PolarDB for MySQL cluster to an Elasticsearch cluster

Prerequisites

• The destination Elasticsearch cluster is created. For more information, see Getting started.
• The available storage space of the destination Elasticsearch cluster is larger than the total size of the data in the source PolarDB for MySQL cluster.

Limits

Billing

Migration types

• Schema migration

  Data Transmission Service (DTS) migrates the schemas of objects from the source database to the destination database.

• 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.

SQL operations that can be migrated during incremental data migration

Permissions required for database accounts

Procedure

1. 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.
2. 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.
3. Click Create Task. On the page that appears, configure the source and destination databases.

   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 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 PolarDB for MySQL.
   	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
   	Instance Region	The region in which the source PolarDB for MySQL cluster resides.
   	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to migrate data across Alibaba Cloud accounts. In this example, No is selected.
   	PolarDB Cluster ID	The ID of the source PolarDB for MySQL cluster.
   	Database Account	The database account of the source PolarDB for MySQL cluster. For more information about the permissions that are required for the account, see the Permissions required for database accounts section of this topic.
   	Database Password	The password of the database account.
   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 database. Select Elasticsearch.
   	Access Method	The access method of the destination database. Select Alibaba Cloud Instance.
   	Instance Region	The region in which the destination Elasticsearch cluster resides.
   	Instance ID	The ID of the destination Elasticsearch cluster.
   	Database Account	The database account of the Elasticsearch cluster. Default value: elastic.
   	Database Password	The password of the database account is the one that is specified when you create the Elasticsearch cluster.

4. In the lower part of the page, click Test Connectivity and Proceed.
   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, and you must make sure that the ECS instance can access the database. 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. For more information about the CIDR blocks of DTS servers, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.

   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.
5. Configure objects to migrate and advanced settings.

   Parameter	Description
   Migration Type	To perform only full data migration, select Schema Migration and Full Data Migration. To ensure service continuity during data migration, select Schema Migration, 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.
   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 tables that have identical table names, the precheck is passed. Otherwise, an error is returned during the precheck and the data migration task cannot be started. Note You can use the object name mapping feature to rename the tables that are migrated to the destination database. You can use this feature if the source and destination databases contain identical table names and the tables in the destination database cannot be deleted or renamed. For more information, see Map object names. 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 schemas, and a data record has the same primary key value as an existing data record in the destination database: During full data migration, DTS does not migrate the data record to the destination database. The existing data record in the destination database is retained. During incremental data migration, DTS migrates the data record to the destination database. The existing data record in the destination database is overwritten. If the source and destination databases have different schemas, data may fail to be initialized. In this case, only some columns are migrated or the data migration task fails.
   Index Name	Table Name If you select Table Name, the index created in the Elasticsearch cluster uses the same name as the table in the PolarDB for MySQL cluster. Database Name_Table Name If you select DatabseName_TableName, the index created in the Elasticsearch cluster is named in the format of Database name_Table name.
   Capitalization of Object Names in Destination Instance	The capitalization of database names, table names, and column names in the destination instance. By default, DTS default policy is selected. You can select other options to make sure that the capitalization of object names is consistent with that in the source or destination database. For more information,see Specify the capitalization of object names in the destination instance.
   Source Objects	Select one or more objects from the Source Objects section. Click the icon and add the objects to the Selected Objects section. Note You can select tables or databases as the objects to be migrated. If you select tables as the objects to be migrated, DTS does not migrate other objects such as views, triggers, and stored procedures to the destination database.
   Selected Objects	To rename an object that you want to migrate to the destination instance, right-click the object in the Selected Objects section. For more information, see Map the name of a single object. To rename multiple objects at a time, click Batch Edit in the upper-right corner of the Selected Objects section. For more information, see Map multiple object names at a time. Note To specify WHERE conditions such as index name, type name, and column name to filter data, right-click an object in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Use SQL conditions to filter data. To select the SQL operations performed on a specific database or table, right-click an object in the Selected Objects section. In the dialog box that appears, select the SQL operations that you want to migrate. For more information about the SQL operations that can be migrated, see the SQL operations that can be migrated during incremental data migration section of this topic.

6. Click Next: 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.
   Source Objects	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 have the same source or destination database, the shortest retry time range that is set 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.
   Shard Configuration	The number of primary shards and replica shards based on the sharding configuration of indexes of the destination Elasticsearch cluster.
   String Index	The method used to compile the strings to the indexes of the destination Elasticsearch cluster. analyzed: The strings are analyzed before indexing. You must select a specific analyzer. For more information about the analyzer types, see Built-in analyzer reference. not analyzed: The strings are indexed with the original values. no: The strings are not indexed.
   Time Zone	The time zone of the date and time data types such as DATETIME and TIMESTAMP. You can select a time zone during the data migration to the destination Elasticsearch cluster. Note If the date and time data types in the destination cluster do not need a time zone, you must specify the document type for the date and time data types.
   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.
   Whether to delete SQL operations on heartbeat tables of forward and reverse tasks	Specifies whether to write SQL operations on heartbeat tables to the source database while the DTS instance is running. Yes: does not write SQL operations on heartbeat tables. In this case, a latency of the DTS instance may be displayed. No: writes SQL operations on heartbeat tables. In this case, specific features such as physical backup and cloning of the source database may be affected.

7. In the lower part of the page, click Next: Configure Database and Table Fields. On the page that appears, set the _routing policy and _id value of the tables that you want to migrate to the destination Elasticsearch cluster.

   Parameter	Description
   Set _routing.	Specifies whether to store a document on a shard of the destination Elasticsearch cluster. For more information, see _routing. If you select Yes, you can specify custom columns for routing. If you select No, the _id value is used for routing. Note If the version of the destination Elasticsearch cluster is 7.x, you must select No.
   Value of _id	Primary key column Multiple columns are merged into one composite primary key. Business key If you select a business key, you must also specify the business key column.

8. 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.
9. Wait until the Success Rate value becomes 100%. Then, click Next: Purchase Instance.
10. Read and select the check box to agree to Data Transmission Service (Pay-as-you-go) Service Terms.
11. Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.
12. Click Buy and Start to start the data migration task. You can view the progress of the task in the task list.