Help Center> Data Replication Service> Real-Time Synchronization> To the Cloud> From DB2 for LUW to GaussDB(DWS)
Updated on 2023-04-26 GMT+08:00
View PDF

From DB2 for LUW to GaussDB(DWS)

Supported Source and Destination Databases

Table 1 Supported databases

Source DB

Destination DB
  • DB2 for LUW

    Versions 9.7, 10.1, 10.5, 11.1, and 11.5
  • GaussDB(DWS)

Prerequisites

  • You have logged in to the DRS console.
  • Your account balance is greater than or equal to $0 USD.
  • For details about the DB types and versions supported by real-time synchronization, see Supported Databases.
  • If a subaccount is used to create a DRS task, ensure that an agency has been added. To create an agency, see Agency Management.

Suggestions

  • When a task is being started or in the full synchronization phase, do not perform DDL operations on the source database. Otherwise, the task may be abnormal.
  • To keep data consistency before and after the synchronization, ensure that no data is written to the destination database during the synchronization.
  • The success of database synchronization depends on environment and manual operations. To ensure a smooth synchronization, perform a synchronization trial before you start the synchronization to help you detect and resolve problems in advance.
  • Start your synchronization task during off-peak hours. A less active database is easier to synchronize successfully. If the data is fairly static, there is less likely to be any severe performance impacts during the synchronization.
    • If network bandwidth is not limited, the query rate of the source database increases by about 50 MB/s during full synchronization, and two to four CPUs are occupied.
    • To ensure data consistency, tables to be synchronized without a primary key may be locked for 3s.
    • The data being synchronized may be locked by other transactions for a long period of time, resulting in read timeout.
    • When DRS concurrently reads data from a database, it will use about 6 to 10 sessions. The impact of the connections on services must be considered.
    • If you read a table, especially a large table, during the full migration, the exclusive lock on that table may be blocked.
    • For more information about the impact of DRS on databases, see What Is the Impact of DRS on Source and Destination Databases?
  • Data-Level Comparison

    To obtain accurate comparison results, start data comparison at a specified time point during off-peak hours. If it is needed, select Start at a specified time for Comparison Time. Due to slight time difference and continuous operations on data, data inconsistency may occur, reducing the reliability and validity of the comparison results.

Precautions

Before creating a synchronization task, read the restrictions listed in the following table.

  • You are advised to create an independent database account for DRS task connection to prevent task failures caused by database account password modification.
  • After changing the account passwords for the source or destination databases, modify the connection information in the DRS task as soon as possible to prevent automatic retry after a task failure. Automatic retry will lock the database accounts.
Table 2 Precautions

Type

Restrictions

Database permissions
  • Source database:
    • To perform full synchronization, the CONNECT and DATAACCESS permissions are required.
    • To perform full+incremental synchronization, the DBADM permission is required.
    • If you select full+incremental synchronization, ensure that the archive log of the source database is enabled and the Datacapture attribute of the table to be synchronized is Y.
    • If there is the DB2SECURITYLABEL data in the table structure of the source database, ensure that the user has the read permission on all data in the table.
  • Destination database:
    • If the destination side does not contain databases, schemas, or tables, the destination database user must have the permission to create databases, the permission to create schemas in a database, or the permission to create tables in a schema.
    • The INSERT, SELECT, UPDATE, and DELETE permissions are required for each table.

Synchronization object constraints
  • During full synchronization, tables, common indexes, primary keys, unique constraints, and data can be synchronized. Tables can be synchronized in real time during incremental synchronization.
  • User-defined types are not supported.
  • The XML type is not supported in the incremental phase.
  • The maximum precision supported by the timestamp type is 6.
  • Full synchronization and structure migration do not support bitmap indexes, inverted indexes, function indexes, and XML indexes.
  • The LOB type supported by incremental synchronization cannot exceed 10 MB.
  • Tables whose default values contain expressions of functions cannot be synchronized.
  • Temporary tables in the source database cannot be synchronized.
  • DDL statements executed in the source database cannot be synchronized.
  • The number of synchronization objects of a single schema in the source database cannot exceed 32,766.
  • If the index name in the source database contains more than 63 characters, the index will be automatically renamed when it is being replayed in the destination database.
  • In incremental synchronization, the Datacapture attribute of the table must be set to Y.

Source database
  • Database object names, such as the database name and table name, support English characters and symbols such as #, $, and _. DRS does not support non-ASCII characters or special characters .>`<'\,|?!" Object names will be converted to lowercase letters after being synchronized to the destination database. To avoid synchronization failures, ensure that the selected source database tables do not contain tables with the same name but different letter cases.
  • If you select full+incremental synchronization, ensure that archive log of the source database is enabled.
  • Only the GBK and UTF8 character sets can be synchronized.

Destination database
  • Ensure that a database named in lowercase letters has been created in destination database.
  • Do not use foreign keys for tables during synchronization. Otherwise, the sequence of writing data to different tables may be inconsistent with that in the source database, which may trigger foreign key constraints and cause synchronization failures.
  • The destination table can contain more columns than the source table. However, the following failures must be avoided:
    • Assume that extra columns on the destination cannot be null or have default values. If newly inserted data records are synchronized from the source to the destination, the extra columns will become null, which does not meet the requirements of the destination and will cause the task to fail.
    • Assume that extra columns on the destination must be fixed at a default value and have a unique constraint. If newly inserted data records are synchronized from the source to the destination, the extra columns will contain multiple default values. That does not meet the unique constraint of the destination and will cause the task to fail.

Precautions
  • Do not use an imprecise value type as the primary key in the database. This feature affects the synchronization of UPDATE and DELETE statements in the DRS incremental scenario and causes value comparison to be unavailable.
  • ARM VMs are not supported.
  • If a table that does not have a primary key contains LOB or LONG data types, data may be inconsistent during incremental synchronization.
  • If the table structure contains the DB2SECURITYLABEL data, reading data in the full phase may be affected by label-based access control (LBAC) of DB2. As a result, data in the source database is inconsistent with that in the destination database.
  • If the character sets of the source database are different from those of the destination database, adjust the field length of the destination database based on the site requirements. For example, the source character set is GBK and the destination character set is UTF8, a Chinese character of GBK occupies two bytes, and a Chinese character of UTF8 occupies three bytes. When CHAR or VARCHAR data type is synchronized to the destination database, the field length may exceed the defined length, so you need to increase the field length to 1.5 times of that in the source database.
  • During synchronization, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases.
  • During the synchronization, the source database cannot contain uncommitted DDL transactions.
  • Full synchronization consists of two phases: table structure synchronization (including indexes) and real-time synchronization. If the structure of a table is created in the destination database, real-time synchronization starts. If a table fails to be synchronized, you can restart the task to synchronize the table data. However, the table structure is not synchronized, so you must manually create the table in the destination database.
  • When the structure of a partitioned table is fully synchronized, the partitioned table is converted to a non-partitioned table.
  • During the full synchronization of table structures, only default value constraints of the character string or number type are supported. Default value constraints of the function or sequence type are not supported. If necessary, create default value constraints for the corresponding table in the destination database.
  • Do not write data to the destination database table during full synchronization. Otherwise, data will be inconsistent.
  • During an incremental synchronization, 0x00 at the end of BLOB and the spaces at the end of CLOB are truncated.
  • You can add additional objects in the incremental synchronization phase.

Procedure

  1. On the Data Synchronization Management page, click Create Synchronization Task.
  2. On the Create Synchronization Instance page, select a region and project, specify the task name, description, and the synchronization instance details, and click Create Now.

    • Task information description
      Figure 1 Synchronization task information
      Table 3 Task and recipient description

      Parameter

      Description

      Region

      The region where the synchronization instance is deployed. You can change the region.

      Project

      The project corresponds to the current region and can be changed.

      Task Name

      The task name must start with a letter and consist of 4 to 50 characters. It can contain only letters, digits, hyphens (-), and underscores (_).

      Description

      The description consists of a maximum of 256 characters and cannot contain special characters !=<>'&"\
    • Synchronization instance information
      Figure 2 Synchronization instance information
      Table 4 Synchronization instance settings

      Parameter

      Description

      Data Flow

      Select To the cloud. The destination database is Databases on the current cloud.

      Source DB Engine

      Select DB2 for LUW.

      Destination DB Engine

      Select GaussDB(DWS).

      Network Type

      The public network is used as an example.

      Available options: Public network, VPC, VPN or Direct Connect

      Destination DB Instance

      The GaussDB(DWS) instance you created.

      Synchronization Instance Subnet

      Select the subnet where the synchronization instance is located. You can also click View Subnet to go to the network console to view the subnet where the instance resides.

      By default, the DRS instance and the destination DB instance are in the same subnet. You need to select the subnet where the DRS instance resides, and there are available IP addresses for the subnet. To ensure that the synchronization instance is successfully created, only subnets with DHCP enabled are displayed.

      Synchronization Mode

      Available options: Full+Incremental and Incremental

      • Full+Incremental

        This synchronization mode allows you to synchronize data in real time. After a full synchronization initializes the destination database, an incremental synchronization parses logs to ensure data consistency between the source and destination databases.

        NOTE:

        If you select Full+Incremental, data generated during the full synchronization will be continuously synchronized to the destination database, and the source remains accessible.

      • Incremental

        Through log parsing, incremental data generated on the source database is synchronized to the destination database.
    • Enterprise Projects and Tags
      Figure 3 Enterprise projects and tags
      Table 5 Enterprise Projects and Tags

      Parameter

      Description

      Enterprise Project

      An enterprise project you would like to use to centrally manage your Global Accelerator resources. Select an enterprise project from the drop-down list. The default project is default. For more information about enterprise project, see Enterprise Management User Guide.

      To customize an enterprise project, click Enterprise in the upper right corner of the console. The Enterprise Management page is displayed. For details, see Creating an Enterprise Project in Enterprise Management User Guide.

      Tags
      • This setting is optional. Adding tags helps you better identify and manage your tasks. Each task can have up to 10 tags.
      • After a task is created, you can view its tag details on the Tags tab. For details, see Tag Management.

    If a task fails to be created, DRS retains the task for three days by default. After three days, the task automatically ends.

  3. On the Configure Source and Destination Databases page, specify source and destination database information and click Test Connection for both the source and destination databases to check whether they have been connected to the synchronization instance. After the connection tests are successful, click Next.

    Figure 4 Source database information
    Table 6 Source database settings

    Parameter

    Description

    IP Address or Domain Name

    IP address or domain name of the source DB2 for LUW database.

    Port

    The port of the source database. Range: 1 – 65535

    Database Username

    The username for accessing the source DB2 for LUW database.

    Database Password

    The password for the source database username.

    Database Name

    The name of the database to which the synchronization objects belong in the source DB2 for LUW.

    SSL Connection

    SSL encrypts the connections between the source and destination databases. If SSL is enabled, upload the SSL CA root certificate. Currently, only DB2 for LUW 10.5 and later versions support SSL. DB2 for LUW 9.7 and 10.1 do not support SSL.

    NOTE:
    • The maximum size of a single certificate file that can be uploaded is 500 KB.
    • If the SSL certificate is not used, your data may be at risk.
    • Three certificate files need to be uploaded for the DB2 for LUW SSL connection: JKS, kdb, and sth
    • DRS does not verify the kdb and sth certificates during the connection test. You need to ensure that the files are correct to prevent subsequent task failures.

    The IP address, username, and password of the source database are encrypted and stored in DRS and will be cleared after the task is deleted.

    Figure 5 Destination database information
    Table 7 Destination database settings

    Parameter

    Description

    DB Instance Name

    The GaussDB(DWS) instance that you selected during task creation and cannot be changed.

    Database Username

    The username for logging in to the destination database.

    Database Password

    Password for the destination database username.

    The username and password of the destination database are encrypted and stored in DRS, and will be cleared after the task is deleted.

  4. On the Set Synchronization Task page, select the synchronization object, enter the name of the destination database, and click Next.

    Figure 6 Synchronization Mode
    Table 8 Synchronization object

    Parameter

    Description

    Synchronization Object Type

    Available options: Table structure, Data, and Constraint

    • Data is selected by default.
    • If Table structure is selected, the destination database cannot contain tables whose names are the same as the source tables to be synchronized.
    • If Table structure is not selected, the destination database must have tables that match the source tables, and the table structure must be the same as the selected source table structures.

    Synchronization Object

    The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables or Import object files for Synchronization Object based on your service requirements.

    • If the synchronization objects in source and destination databases have different names, you can map the source object name to the destination one. For details, see Mapping Object Names.
    NOTE:
    • To quickly select the desired database objects, you can use the search function.
    • If there are changes made to the source databases or objects, click in the upper right corner to update the objects to be synchronized.
    • If the object name contains spaces, the spaces before and after the object name are not displayed. If there are multiple spaces between the object name and the object name, only one space is displayed.
    • The name of the selected synchronization object cannot contain spaces.

  5. On the Check Task page, check the synchronization task.

    • If any check fails, review the cause and rectify the fault. After the fault is rectified, click Check Again.

      For details about how to handle check failures, see Checking Whether the Source Database Is Connected in Data Replication Service User Guide.

    • If all check items are successful, click Next.
      Figure 7 Pre-check

      You can proceed to the next step only when all checks are successful. If there are any items that require confirmation, view and confirm the details first before proceeding to the next step.

  6. On the displayed page, specify Start Time, Send Notification, SMN Topic, Synchronization Delay Threshold, and Stop Abnormal Tasks After, confirm that the configured information is correct, select the check box before the agreement, and click Submit to submit the task.

    Figure 8 Task startup settings
    Table 9 Task startup settings

    Parameter

    Description

    Started Time

    Set Start Time to Start upon task creation or Start at a specified time based on site requirements.

    NOTE:

    After a synchronization task is started, the performance of the source and destination databases may be affected. You are advised to start a synchronization task during off-peak hours.

    Send Notifications

    SMN topic. This parameter is optional. If an exception occurs during synchronization, the system will send a notification to the specified recipients.

    SMN Topic

    This parameter is available only after you enable Send Notifications and create a topic on the SMN console and add a subscriber.

    For details, see Simple Message Notification User Guide.

    Synchronization Delay Threshold

    During an incremental synchronization, a synchronization delay indicates a time difference (in seconds) of synchronization between the source and destination database.

    If the synchronization delay exceeds the threshold you specify, DRS will send alarms to the specified recipients. The value ranges from 0 to 3,600. To avoid repeated alarms caused by the fluctuation of delay, an alarm is sent only after the delay has exceeded the threshold for six minutes.

    NOTE:
    • If the delay threshold is set to 0, no notifications will be sent to the recipient.
    • In the early stages of an incremental synchronization, the synchronization delay is long because a large quantity of data is awaiting synchronization. In this case, no notifications will be sent.
    • Before setting the delay threshold, enable Send Notification.

    Stop Abnormal Tasks After

    Number of days after which an abnormal task is automatically stopped. The value must range from 14 to 100. The default value is 14.

    NOTE:

    Tasks in the abnormal state are still charged. If tasks remain in the abnormal state for a long time, they cannot be resumed. Abnormal tasks run longer than the period you set (unit: day) will automatically stop to avoid unnecessary fees.

  7. After the task is submitted, you can view and manage it on the Data Synchronization Management page.

    • You can view the task status. For more information about task status, see Task Statuses.
    • You can click in the upper-right corner to view the latest task status.
    • By default, DRS retains a task in the Configuration state for three days. After three days, DRS automatically deletes background resources, and the task status remains unchanged. When you restart the task configuration, DRS applies for resources again.

Parent topic: To the Cloud