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Data Transmission Service:Synchronize data from a PolarDB-X 2.0 instance to an Elasticsearch cluster

Last Updated:Jul 12, 2023

This topic describes how to synchronize data from a PolarDB-X 2.0 instance to an Elasticsearch cluster by using Data Transmission Service (DTS).

Prerequisites

  • The source PolarDB-X 2.0 instance that is compatible with MySQL 5.7 is created.

  • The destination Elasticsearch cluster is created. For more information, see Create an Alibaba Cloud Elasticsearch cluster.

  • The engine versions of the source instance and the destination cluster are supported. For more information, see Overview of data synchronization scenarios.

  • The available storage space of the destination Elasticsearch cluster is larger than the total size of the data in the source PolarDB-X 2.0 instance.

Limits

Note
  • During schema synchronization, DTS synchronizes foreign keys from the source database to the destination database.
  • During full synchronization and incremental synchronization, DTS temporarily disables checking of foreign key constraints and foreign key cascade operations at the session level. If you perform the cascade update and delete operations on the source database during data synchronization, data inconsistency may occur.
CategoryDescription
Limits on the source database
  • The tables to be migrated must have PRIMARY KEY or UNIQUE constraints, and all fields must be unique. Otherwise, the destination database may contain duplicate data records.
  • If you select tables as the objects to synchronize and you need to edit tables (such as renaming tables or columns) in the destination database, you can synchronize up to 5,000 tables in a single data synchronization task. If you run a task to synchronize more than 5,000 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 following requirements for binary logs must be met:
    • The binary logging feature must be enabled in the PolarDB-X 2.0 console. For more information, see Parameter settings. The binlog_row_image parameter value is set to full. 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 are retained for at least 24 hours. If you perform both full data synchronization and incremental data synchronization, the binary logs of the source database are retained for at least seven days. After full data synchronization is complete, you can set the retention period to more than 24 hours. Otherwise, DTS may fail to obtain the binary logs and the task may fail. In exceptional circumstances, data inconsistency or loss may occur. Make sure that you set the retention period of binary logs in accordance with the preceding requirements. Otherwise, the service reliability and performance stated in the Service Level Agreement (SLA) of DTS cannot be achieved.

  • The PolarDB-X 2.0 instance must be compatible with MySQL V5.7.
Other limits
  • DTS cannot be used to synchronize DDL operations. If a DDL operation is performed on a source table during data synchronization, you must remove the table from the data synchronization task. Then, you must remove the index that corresponds to the table from your Elasticsearch cluster, and add the table to the data synchronization task again. For more information, see Remove an object from a data synchronization task and Add an object to a data synchronization task.
  • If you want to add columns to a source table, modify the mappings of the index that corresponds to the table in the Elasticsearch cluster. Then, perform DDL operations on the source table, pause the data synchronization task, and start the task again.
  • 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 initial 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.
  • During initial full data synchronization, concurrent INSERT operations cause fragmentation in the tables of the destination database. After full data synchronization is complete, the size of used tablespace of the destination database is larger than that of the source database.
  • We recommend that you do not use pt-online-schema-change to perform DDL operations on objects. Otherwise, data synchronization may fail.
  • During data synchronization, we recommend that you use only DTS to write data to the destination database. This prevents data inconsistency between the source and destination databases. If you use tools other than DTS to write data to the destination database, data loss may occur in the destination database when you use DMS to perform online DDL operations.
PrecautionsDTS 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 typeTask configuration fee
Schema synchronization and full data synchronizationFree of charge.
Incremental data synchronizationCharged. For more information, see Billing overview.

Supported synchronization topologies

  • One-way one-to-one synchronization

  • One-way one-to-many synchronization

  • One-way many-to-one synchronization

For more information about the synchronization topologies that are supported by DTS, see Synchronization topologies.

SQL operations that can be synchronized

Operation type

SQL statement

DML

INSERT, UPDATE, and DELETE

Mappings

The MySQL data types supported by PolarDB-X 2.0 do not match the data types supported by Elasticsearch. DTS converts the data types of the source database to those of the Elasticsearch cluster during schema synchronization based on the data type mappings for schema synchronization. For more information, see Data type mappings for schema synchronization.

Procedure

  1. 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
  2. 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.
  3. 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 in the upper part of the page. This helps you create and run the data synchronization task.

    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

    Database Type

    The type of the source database. Select PolarDB-X 2.0.

    Access Method

    The access method of the source database. Select Alibaba Cloud Instance.

    Instance Region

    The region in which the source PolarDB-X 2.0 instance resides.

    Instance ID

    The ID of the source PolarDB-X 2.0 instance.

    Database Account

    The database account of the source PolarDB-X 2.0 instance. The account must have the SELECT permission on the objects to be synchronized, and the REPLICATION CLIENT and REPLICATION SLAVE permissions.

    Note

    For more information about how to grant the permissions to the database account, see Permissions required for an account to synchronize data.

    Database Password

    The password of the database account.

    Destination 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 destination Elasticsearch cluster. The default database account in Elasticsearch clusters is elastic and must have the read and write permissions on the objects to be synchronized.

    Database Password

    The password of the database account.

  4. In the lower part of the page, 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, DTS automatically adds the CIDR blocks of DTS servers to the whitelist of the 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 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 need to manually add the CIDR blocks of DTS servers to the whitelist of the self-managed database on the ECS instance to allow DTS to 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.
    • If the CIDR blocks of DTS servers are automatically or manually added to the whitelist or 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.
    • After the DTS task is complete or released, we recommend that you manually remove the CIDR blocks of DTS servers from the whitelist or ECS security group rules. You must remove the IP address whitelist group whose name contains dts from the whitelist of the Alibaba Cloud database instance or the security group rules of the ECS instance. For more information about the CIDR blocks that you must remove from the whitelist of the self-managed databases that are deployed in data centers or databases that are hosted on third-party cloud services, see Add the CIDR blocks of DTS servers to the security settings of on-premises databases.
  5. Select objects for the task and configure advanced settings.

    Parameter

    Description

    Task Stages

    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 the selected objects from the source database to the destination database. The historical data is the basis for subsequent incremental synchronization.

    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 synchronization task cannot be started.

      Note You can use the object name mapping feature to rename the tables that are synchronized 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 synchronization, DTS does not synchronize the data record to the destination database. The existing data record in the destination database is retained.
        • During incremental data synchronization, DTS synchronizes 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 synchronized or the data synchronization task fails.

    Index Name

    • Table Name

      If you select Table Name, the created index name in the destination Elasticsearch cluster is the same as the table name. In this example, order is used.

    • DatabaseName_TableName

      If you select Database Name_Table Name, the created index name in the destination Elasticsearch cluster is in the format of Database name_Table name. In this example, dtstest_order is used.

    Source Objects

    Select one or more objects from the Source Objects section and click the Rightwards arrow icon to add the objects to the Selected Objects section.

    Note You can select columns, tables, or databases as the objects to be synchronized. If you select tables or columns as the objects to be synchronized, DTS does not synchronize other objects such as views, triggers, or stored procedures to the destination database.

    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 select the SQL operations performed on a specific database or table, perform the following steps: In the Selected Objects section, right-click an object. In the dialog box that appears, select the SQL operations that you want to synchronize. For more information about the SQL operations that can be synchronized, see the SQL operations that can be synchronized section of this topic.

    • To specify WHERE conditions 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.

    • 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.

  6. Click Next: Advanced Settings to configure advanced settings.

    Parameter

    Description

    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:

    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 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 the earliest opportunity after the source and destination instances are released.

    Shard Configuration

    The number of primary shards and replica shards based on the shard 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 synchronization 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.

    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.

  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 synchronize to the destination Elasticsearch cluster.
    Set _routing
    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 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 analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
    • If an alert is generated for an item during the precheck, perform the following operations based on the scenario:
      • In scenarios where you cannot ignore the alert item, click View Details next to the failed item. After you analyze the causes based on the check results, troubleshoot the issues. Then, run a precheck again.
      • In scenarios where you can ignore the alert item, click Confirm Alert Details next to the failed item. 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 becomes 100%. Then, click Next: Purchase Instance.
  10. 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.
    Instance Class DTS provides several instance classes that have different performance in synchronization speed. You can select an instance class 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 or one to three years.
    Note This parameter is displayed only if you select the subscription billing method.
  11. Read and select the check box for Data Transmission Service (Pay-as-you-go) Service Terms.
  12. Click Buy and Start to start the data synchronization task. You can view the progress of the task in the task list.

Check the index and data

After the state of the data synchronization task changes to Running, you can use the data visualization tool Kibana to connect to the Elasticsearch cluster. This way, you can check whether the index is created and data is synchronized as expected. For more information about how to log on to the Kibana console, see Log on to the Kibana console.

Note

If the index is not created or data is not synchronized as expected, you can delete the index and data, and then configure the data synchronization task again.