If you want to synchronize data from Oracle to Hologres, the source is Oracle, and the destination is Hologres. Before you run a data synchronization task, you must refer to the operations in this topic to prepare the configurations, such as network environments and whitelists, for both the source and destination.

Prerequisites

Before you configure a data source, make sure that the following operations are performed:
  • Prepare data sources: A source Oracle data source and a destination Hologres data source are created.
  • Plan and prepare resources: An exclusive resource group for data integration is purchased and configured. For more information, see Plan and configure resources.
  • Evaluate and plan the network environment: Before you perform data integration, connect data sources to exclusive resource groups for data integration based on your business requirements. After data sources and exclusive resource groups for data integration are connected, you can refer to the operations in this topic to configure access settings such as vSwitches and whitelists.
    • If data sources and exclusive resource groups for data integration reside in the same region and virtual private cloud (VPC), they are automatically connected.
    • If data sources and exclusive resource groups for data integration reside in different network environments, you must connect data sources and resource groups by using methods such as a VPN gateway.

Background information

Before you synchronize data from source data sources to destination data sources, make sure that data sources and exclusive resource groups for data integration are connected. You must also make sure that the exclusive resource groups for data integration can be used to access the data sources. In addition, the Oracle data source must contain only the character encoding formats and data types that are supported for data integration.
  • Configure whitelists for data sources
    If data sources and exclusive resource groups for data integration reside in the same VPC, you need to add the CIDR block of the exclusive resource group to the whitelists of data sources. This ensures that the exclusive resource group for data integration can be used to access data sources.VPC connection
  • Create an account and authorize the account

    You must create an account that can be used to access data sources, read data from the source data source, and write data to the destination data source in the data integration process.

  • Enable generation of database-level redo log files and enable database-level supplemental logging
    You must enable generation of database-level redo log files and enable database-level supplemental logging for the Oracle database to be configured as a source data source.
    • Redo log files: Oracle uses redo log files to ensure that database transactions can be re-executed. This way, data can be recovered in the case of a failure such as power outage.
    • Supplemental logging: Supplemental logging is used to supplement the information recorded in redo log files. In Oracle, a redo log file is used to record the values of the fields that are modified. Supplemental logging is used to supplement the change history in the redo log file. This ensures that the redo log file contains complete information that describes data changes. If operations such as data recovery and data synchronization are performed, you can view complete statements and data updates. Some features of the Oracle database can be better implemented after supplemental logging is enabled. Therefore, you must enable supplemental logging for the database.

      For example, if you do not enable supplemental logging, after you execute the UPDATE statement, the redo log file records only the values of the fields that are modified when the UPDATE statement is executed. If you enable supplemental logging, the redo log file records the values of fields before and after a modification. The conditions that are used to modify destination fields are also recorded. When an exception such as power outage occurs in the database, you can recover data based on the modification details.

      We recommend that you enable supplemental logging for primary key columns or unique index columns.
      • After you enable supplemental logging for primary key columns, the columns that compose a primary key are recorded in logs if the database is updated.
      • After you enable supplemental logging for unique index columns, the columns that compose a unique key or bitmap index are recorded in logs if a column is modified.
  • Check character encoding formats

    You must make sure that the Oracle database contains only the character encoding formats that are supported for data integration to prevent a data synchronization failure. The following encoding formats are supported for data synchronization: UTF-8, AL32UTF8, AL16UTF16, and ZHS16GBK.

  • Check data types

    You must make sure that the Oracle database contains only the data types that are supported for data integration to prevent data synchronization failures. The following data types are not supported for real-time data synchronization: LONG, BFILE, LONG RAW, and NCLOB.

Limits

  • You can configure the supplemental logging feature only in a primary Oracle database. Supplemental logging can be enabled for a primary or secondary database.
  • The following encoding formats are supported for data synchronization: UTF-8, AL32UTF8, AL16UTF16, and ZHS16GBK.
  • The following data types are not supported for real-time data synchronization: LONG, BFILE, LONG RAW, and NCLOB.

Procedure

  1. Configure a whitelist for an Oracle database.
    Add the CIDR block of the VPC where the exclusive resource group resides to the whitelist of the Oracle database.
    1. View and record the EIP and CIDR block of the exclusive resource group.
    2. Add the EIP and CIDR block of the exclusive resource group to the whitelist of the Oracle database.
  2. Create an account and grant the required permissions to the account.
    You must create an account to log on to the database. The account must have the required permissions on the Oracle database.
    1. Create an account.
      For more information, see Create an Oracle database account.
    2. Grant permissions to the account.
      You can run the following commands to grant permissions to the account. Replace Account for data synchronization with the created account when you execute the specific statement.
      grant create session to 'Account for data synchronization';  // Authorize the synchronization account to access the database.
      grant connect to 'Account for data synchronization';  // Authorize the synchronization account to connect to the database.
      grant select on nls_database_parameters to 'Account for data synchronization';  // Authorize the synchronization account to query the settings of nls_database_parameters.
      grant select on all_users to 'Account for data synchronization';  // Authorize the synchronization account to query all users in the database.
      grant select on all_objects to 'Account for data synchronization';  // Authorize the synchronization account to query all objects in the database.
      grant select on DBA_MVIEWS to 'Account for data synchronization';  // Authorize the synchronization account to check the materialized view of the database.
      grant select on DBA_MVIEW_LOGS to 'Account for data synchronization';  // Authorize the synchronization account to view the materialized view logs of the database.
      grant select on DBA_CONSTRAINTS to 'Account for data synchronization';  // Authorize the synchronization account to view the constraints on all tables of the database.
      grant select on DBA_CONS_COLUMNS to 'Account for data synchronization';  // Authorize the synchronization account to view information about all columns under specified constraints on all tables of the database.
      grant select on all_tab_cols to 'Account for data synchronization';  // Authorize the synchronization account to view information about columns in tables, views, and clusters of the database.
      grant select on sys.obj$ to 'Account for data synchronization';  // Authorize the synchronization account to view objects in the database. sys.obj$ indicates an object table that is contained in the data dictionary table. The object table contains all objects.
      grant select on SYS.COL$ to 'Account for data synchronization';  // Authorize the synchronization account to view definitions of columns in tables of the database. SYS.COL$ stores column definitions.
      grant select on sys.USER$ to 'Account for data synchronization';  // Authorize the synchronization account to view the system table of the database. sys.USER$ indicates a default user session service.
      grant select on sys.cdef$ to 'Account for data synchronization';  // Authorize the synchronization account to view the system table of the database.
      grant select on sys.con$ to 'Account for data synchronization';  // Authorize the synchronization account to view the constraints of the database. sys.con$ records the constraints.
      grant select on all_indexes to 'Account for data synchronization';  // Authorize the synchronization account to view all indexes of the database.
      grant select on v_$database to 'Account for data synchronization';  // Authorize the synchronization account to check the v_$database view of the database.
      grant select on V_$ARCHIVE_DEST to 'Account for data synchronization';  // Authorize the synchronization account to check the V_$ARCHIVE_DEST view of the database.
      grant select on v_$log to 'Account for data synchronization';  // Authorize the synchronization account to check the v_$log view of the database. v_$log displays log information about control files.
      grant select on v_$logfile to 'Account for data synchronization';  // Authorize the synchronization account to check the v_$logfile view of the database. v_$logfile contains information about redo log files.
      grant select on v_$archived_log to 'Account for data synchronization';  // Authorize the synchronization account to check the v$archived_log view of the database. v$archived_log contains information about archived logs.
      grant select on V_$LOGMNR_CONTENTS to 'Account for data synchronization';  // Authorize the synchronization account to check the V_$LOGMNR_CONTENTS view of the database.
      grant select on DUAL to 'Account for data synchronization';   // Authorize the synchronization account to view the DUAL table of the database. DUAL is a virtual table that contains SELECT syntax rules. In Oracle, only one record is retained in the DUAL table.
      grant select on v_$parameter to 'Account for data synchronization';  // Authorize the synchronization account to check the v_$parameter view of the database. v$parameter is a dynamic dictionary table that stores the values of parameters in the database.
      grant select any transaction to 'Account for data synchronization';  // Authorize the synchronization account to view transactions of the database.
      grant execute on SYS.DBMS_LOGMNR to 'Account for data synchronization';  // Authorize the synchronization account to use the LOGMNR tool. The LOGMNR tool helps you analyze transactions and retrieve lost data.
      grant alter session to 'Account for data synchronization';  // Authorize the synchronization account to modify connection configurations of the database.
      grant select on dba_objects to 'Account for data synchronization';  // Authorize the synchronization account to view all objects of the database.
      grant select on v_$standby_log to 'Account for data synchronization';  // Authorize the synchronization account to check the v_$standby_log view of the database. v_$standby_log contains archived logs of the secondary database.
      grant select on v_$ARCHIVE_GAP to 'Account for data synchronization';  // Authorize the synchronization account to query missing archived logs.
      To synchronize full offline data, you must also run the following command to grant the query permission on all tables to the synchronization account:
      grant select any table to 'Account for data synchronization'; 
      In Oracle 12c and later, you must run the following command to grant the log mining permission to the synchronization account. The log mining feature is built in Oracle versions earlier than 12c. You do not need to run the command in these versions.
      grant LOGMINING TO 'Account for data synchronization';
  3. Enable supplemental logging and switch a redo log file.
    Log on to the primary database and perform the following steps:
    1. Enable supplemental logging.

      SQL statements:

      alter database add supplemental log data(primary key) columns; // Enable supplemental logging for primary key columns.
      alter database add supplemental log data(unique) columns; // Enable supplemental logging for unique index columns.
    2. Switch a redo log file.
      After you enable supplemental logging, you must run the following command multiple times to switch a redo log file. We recommend that you run the following command for five times:
      alter system switch logfile;
      Note This ensures that data can be written to the next log file after the current log file is full. Data about historical operations will not be lost. This facilitates data recovery.
  4. Check character encoding formats of the database.
    Run the following command to check character encoding formats of the database:
    select * from v$nls_parameters where PARAMETER IN ('NLS_CHARACTERSET', 'NLS_NCHAR_CHARACTERSET');
    • v$nls_parameters stores values of parameters in the database.
    • NLS_CHARACTERSET indicates a database character set. NLS_NCHAR_CHARACTERSET indicates a national character set. These two sets are used to store data of the character type.
    The following encoding formats are supported for data synchronization: UTF-8, AL32UTF8, AL16UTF16, and ZHS16GBK. If the database contains the character encoding formats that are not supported for data synchronization, change the formats before you synchronize data.
  5. Check the data types of tables in the database.
    You can execute the SELECT statement to query the data types of tables in the database. Sample statement that is executed to query the data types of the 'tablename' table:
    select COLUMN_NAME,DATA_TYPE from all_tab_columns where TABLE_NAME='tablename'; 
    • COLUMN_NAME: the name of the column.
    • DATA_TYPE: the data type of the column.
    • all_tab_columns: the view that stores information about all columns in tables of the database.
    • TABLE_NAME: the name of the destination table for a query. When you execute the preceding statement, replace 'tablename' with the name of the destination table for a query.
    You can also execute the select * from 'tablename'; statement to query the information about the destination table and obtain data types.
    The following data types are not supported for real-time data synchronization: LONG, BFILE, LONG RAW, and NCLOB. If a table contains one of these data types, remove the table from the real-time synchronization solution list or change the data type before you synchronize data.

What to do next

After data sources are configured, the source data source, destination data source, and exclusive resource group for data integration are connected. Then, the exclusive resource group for data integration can be used to access data sources. You can add the source data source and destination data source to DataWorks, and associate them with a data synchronization solution when you create the solution.

For more information about how to add a data source, see Add a data source.