Synchronize data from a PolarDB-X 1.0 instance to an Elasticsearch cluster - Data Transmission Service

This topic describes how to synchronize data from a PolarDB-X 1.0 instance to an Elasticsearch cluster by using Data Transmission Service (DTS).

Prerequisites

The storage type of the source PolarDB-X 1.0 instance is ApsaraDB RDS for MySQL, including custom ApsaraDB RDS instances and purchased ApsaraDB RDS instances. PolarDB for MySQL is not supported as the storage type.
The destination Elasticsearch cluster is created. For more information, see Create an Alibaba Cloud Elasticsearch cluster.
The available storage space of the destination Elasticsearch cluster is larger than the total size of the data in the source PolarDB-X 1.0 instance.

Limits

Category	Description
Limits on the source database	The tables to be synchronized must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination database may contain duplicate data records. The tables that only have UNIQUE constraints do not support schema synchronization. Therefore, we recommend that you synchronize the tables that have PRIMARY KEY constraints. The tables that have secondary indexes cannot be synchronized. If you select tables as the objects to be synchronized and you need to modify the tables in the destination database, such as renaming tables or columns, you can synchronize up to 1,000 tables in a single data synchronization task. If you run a task to synchronize more than 1,000 tables, a request error occurs. In this case, we recommend that you configure multiple tasks to synchronize the tables in batches or configure a task to synchronize the entire database. The ApsaraDB RDS for MySQL instances attached to the PolarDB-X 1.0 instance must meet the following requirements for binary logs: By default, the binary logging feature is enabled for an ApsaraDB RDS for MySQL instance. Make sure that the binlog_row_image parameter is set to full. For more information, see View the parameters of an ApsaraDB RDS for MySQL instance. Otherwise, error messages are returned during the precheck and the data synchronization task cannot be started. If you perform only incremental data synchronization, the binary logs of the source database must be retained for at least 24 hours. If you perform both full data synchronization and incremental data synchronization, the binary logs of the source database must be retained for at least seven days. Otherwise, DTS may fail to obtain the binary logs, which causes the task to fail, or even data inconsistency and data loss. After full data synchronization is complete, you can set the retention period to more than 24 hours. Make sure that you set the retention period of binary logs based on the preceding requirements. Otherwise, the Service Level Agreement (SLA) of DTS does not guarantee service reliability or performance. Limits on operations to be performed on the source database: If you change the network type of the PolarDB-X 1.0 instance during data synchronization, you must also modify the network connection information of the data synchronization task. During data synchronization, do not scale the capacity of the source instance, synchronize frequently accessed tables, change shards, or perform DDL operations. Otherwise, the data synchronization task fails or data inconsistency occurs. If you perform only full data synchronization, do not write data to the source instance during data synchronization. Otherwise, data inconsistency may occur between the source and destination instances. To ensure data consistency, we recommend that you select schema synchronization, full data synchronization, and incremental data synchronization as the synchronization types.
Other limits	To add columns to a table that you want to synchronize, perform the following operations: Modify the mappings of the table in the Elasticsearch cluster, perform DDL operations in the source PolarDB-X 1.0 instance, and then pause and start the data synchronization task. Before you 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. During full data synchronization, DTS uses the read and write resources of the source and destination databases. This may increase the loads on the database servers. DTS attempts to resume data synchronization tasks that failed within the last seven days. Before you switch workloads to the destination instance, 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 instance. Otherwise, the data in the source instance overwrites the data in the destination instance after a failed task is resumed.
Special cases	DTS updates the `dts_health_check`.`ha_health_check` table in the source database as scheduled to move forward the binary log file position.

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.

SQL operations that can be incrementally synchronized

Operation type	SQL statement
DML	INSERT, UPDATE, and DELETE

Data type mappings

For more information, see Data type mappings for schema synchronization.

Permissions required for database accounts

Instance type	Required permission	References
Source PolarDB-X 1.0 instance	The read permissions on the objects to be synchronized.	Manage accounts
Destination Elasticsearch cluster	The read and write permissions on the destination cluster. In most cases, the account is elastic.

Procedure

Go to the Data Synchronization Tasks page.
1. Log on to the DMS console.
2. In the top navigation bar, click DTS.
3. In the left-side navigation pane, choose DTS (DTS) > Data Synchronization.
Note
- The actual operation may vary depending on the mode and layout of DMS. For more information, see Simple mode and Customize the layout and style of the DMS console.
- 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 you want to create the data synchronization task.
Note
If you use the new DTS console, select the region in which you want to create the data synchronization task in the upper-left corner of the page.

Click Create Task. In the Create Task wizard, configure the source and destination databases.

Section	Parameter	Description
N/A	Task Name	The name of the task. DTS automatically assigns a name to the task. 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 an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the database.
	Database Type	The type of the source database. Select PolarDB-X 1.0.
	Access Method	The access method of the source database. Select Alibaba Cloud Instance.
	Instance Region	The region in which the source PolarDB-X 1.0 instance resides.
	Replicate Data Across Alibaba Cloud Accounts	Specifies whether to synchronize data across Alibaba Cloud accounts. In this example, No is selected.
	Instance ID	The ID of the source PolarDB-X 1.0 instance.
	Database Account	The database account of the source PolarDB-X 1.0 instance.
	Database Password	The password of the database account.
Destination Database	Select an existing DMS database instance. (Optional. If you have not registered a DMS database instance, ignore this option and configure database settings in the section below.)	The database instance that you want to use. You can choose whether to select an existing instance based on your business requirements. If you select an existing instance, DTS automatically populates the parameters for the database. If you do not select an existing instance, you must manually configure parameters for the 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 username that is used to connect to the Elasticsearch cluster. Enter the username that you specified when you created the Elasticsearch cluster. The default account in an Elasticsearch clusters is elastic.
	Database Password	The password of the database account.

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 ensure 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, 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 the database or instance, or to the ECS security group rules, security risks may arise. Therefore, before you use DTS to synchronize 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.

Configure the objects to be synchronized and advanced settings.

Parameter	Description
Synchronization Types	By default, Incremental Data Synchronization is selected. You must also select Schema Synchronization and Full Data Synchronization. After the precheck is complete, DTS synchronizes the historical data of selected objects from the source instance to the destination instance. The historical data is the basis for subsequent incremental synchronization.
Processing Mode of Conflicting Tables	Precheck and Report Errors: checks whether the destination cluster contains indexes that have the same names as the source tables. If the destination cluster does not contain indexes that have the same names as the source tables, the precheck is passed. Otherwise, an error is returned during the precheck and the data synchronization task cannot be started. Note You can use the object name mapping feature to rename the tables that are synchronized to the destination cluster. You can use this feature if the source instance and destination cluster contain identical table names and the tables in the destination cluster cannot be deleted or renamed. For more information, see Rename an object to be synchronized. Ignore Errors and Proceed: skips the precheck for indexes in the destination cluster that have the same names as the source tables. Warning If you select Ignore Errors and Proceed, data inconsistency may occur and your business may be exposed to the following potential risks: If the source instance and destination cluster have the same mappings and the primary key of a record in the destination cluster is the same as that in the source instance, the record remains unchanged during initial data synchronization. However, the record is overwritten during incremental data synchronization. If the source instance and destination cluster have different mappings, initial data synchronization may fail. In this case, only some columns are synchronized or the data synchronization task fails.
Index Name	If you select Table Name, the index created in the destination Elasticsearch cluster uses the same name as the table in the PolarDB-X 1.0 instance. If you select Database Name_Table Name, the index created in the destination Elasticsearch cluster is named in the format of Database name_Table name. Note The index name mapping rule takes effect for all tables.
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 ensure 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 and click the icon to add the objects to the Selected Objects section. Note You can select tables or databases as the objects to be synchronized.
Selected Objects	To rename an object that you want to synchronize 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 to filter data, right-click a table in the Selected Objects section. In the dialog box that appears, specify the conditions. For more information, see Use SQL conditions to filter data. If you use the object name mapping feature to rename an object, other objects that are dependent on the object may fail to be synchronized.

Click Next: Advanced Settings to configure advanced settings.

Parameter	Description
Select the dedicated cluster used to schedule the task	By default, DTS schedules tasks to shared clusters. You do not need to configure this parameter. You can purchase a dedicated cluster of specified specifications to run DTS synchronization tasks. For more information, see What is a DTS dedicated cluster.
Set Alerts	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 configure alerting. Yes: configures alerting. In this case, you must also configure 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 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 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 synchronization task. Otherwise, the data synchronization task fails. Note If you set different retry time ranges for multiple DTS 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.
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 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 the 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 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 Connection parameter.
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 configure the Queries per second (QPS) to the source database, RPS of Full Data Migration, and BPS of Full Data Migration parameters for full data synchronization tasks to reduce the pressure on the destination database. Note This parameter can be configured only if Full Data Synchronization is selected as Synchronization Types.
Enable Throttling for Incremental Data Synchronization	You can configure the RPS of Incremental Data Migration and BPS of Incremental Data Migration parameters for incremental data synchronization tasks to reduce the pressure on the destination database.
Environment Tag	The environment tag that is used to identify the DTS instance. You can select an environment tag based on your business requirements.
Shard Configuration	The number of primary shards and replica shards based on the shard configurations of indexes of the destination Elasticsearch cluster.
String Index	The method used to index the strings that are synchronized to the destination Elasticsearch cluster. Valid values: 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 for synchronizing date and time data 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 in the destination cluster before you perform data synchronization.
DOCID	The default value of the parameter is the primary key of the table in the Elasticsearch cluster. If the table does not have a primary key, the value of the parameter is the ID column that is automatically generated by Elasticsearch.
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: Configure Database and Table Fields. On the page that appears, set the _routing policy and _id value of the tables that you want to synchronize to the destination Elasticsearch cluster.

Parameter	Description
Set _routing	Specifies whether to store a document on a specific shard of the destination Elasticsearch cluster. For more information, see _routing. Valid values: Yes: You can specify custom columns for routing. No: The _id value is used for routing. Note If the version of the destination Elasticsearch cluster is 7.x, you must select No.
_routing Column	The column that is used for routing. Note This parameter is required only if the Set _routing parameter is set to Yes.
Value of _id	The column that is used to store the IDs of documents.

Click Next: Save Task Settings and Precheck in the lower part of the page.
You can move the pointer over Next: Save Task Settings and Precheck and click Preview OpenAPI parameters to view the parameter settings of the API operation that is called to configure the instance.
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 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, 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 the instance when you create an 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 charged 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 instance, you can release the pay-as-you-go instance to reduce costs.
	Resource Group	The resource group on which the instance is run. Default value: default resource group. For more information, see What is Resource Management?.
	Instance Class	DTS provides various synchronization specifications that provide different performance. The synchronization speed varies based on the synchronization specifications that you select. You can select a synchronization specification based on your business scenario. For more information, see Specifications of data synchronization instances.
	Subscription Duration	If you select the subscription billing method, set the subscription duration and the number of 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 the check box to agree to the Data Transmission Service (Pay-as-you-go) Service Terms.
Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.
Wait until the success rate becomes 100%. Then, click Next: Purchase Instance.