From Oracle to GaussDB Primary/Standby

Supported Source and Destination Databases

**Table 1** Supported databases
Source DB	Destination DB
On-premises databases ECS databases	GaussDB primary/standby

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.
- 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, compare data 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 following notes:

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: Full synchronization requires the following permissions: CREATE SESSION, SELECT ANY DICTIONARY, and SELECT for single tables (GRANT SELECT <userName.tbName> to drsUser) Full+incremental synchronization and incremental synchronization: To synchronize a container database (CDB) of Oracle 12c or later, you must have the following permissions: CREATE SESSION, SELECT ANY DICTIONARY, SELECT for a single table (GRANT SELECT <userName.tbName> to drsUser), EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, LOGMINING, SELECT ON SYS.COL$, SELECT ON SYS.OBJ$, and SET CONTAINER (GRANT SET CONTAINER TO <userName> CONTAINER=ALL). To synchronize a pluggable database (PDB) of Oracle 12c or later, you must have the following permissions: CREATE SESSION, SELECT ANY DICTIONARY, SELECT for a single table (GRANT SELECT <userName.tbName> to drsUser), EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, LOGMINING, SELECT ON SYS.COL$, and SELECT ON SYS.OBJ$, and CREATE SESSION, SELECT ANY DICTIONARY, EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, LOGMINING and SET CONTAINER (GRANT SET CONTAINER TO <userName> CONTAINER=ALL) permissions for a CDB. To synchronize a database of Oracle 11g or earlier, you must have the following permissions: CREATE SESSION, SELECT ANY DICTIONARY, SELECT for a single table (GRANT SELECT <userName.tbName> to drsUser), EXECUTE_CATALOG_ROLE, SELECT ANY TRANSACTION, SELECT ON SYS.COL$, and SELECT ON SYS.OBJ$. During incremental synchronization, enable PK, UK, or ALL supplemental logging for the source Oracle database at the database level or table level. If supplemental logging is enabled at table level, enable supplemental logging again after you rebuild or rename tables. During the synchronization, ensure that the preceding settings are always enabled. Oracle 12c or later does not support incremental synchronization using accounts whose ORACLE_MAINTAINED is Y (except system/sys), because accounts with this attribute do not have the permission to parse logs. Destination database: Database-level permissions: Log in to the postgres base database as user root or user DATABASE with the Sysadmin role, and grant the CREATE and CONNECT permissions to user DATABASE. Schema-level permission: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the database, and grant the CREATE and USAGE permissions of the schema to the user. Table-level permission: Log in to the database as user root or user DATABASE with the Sysadmin role, or the owner of the database, and grant the SELECT, UPDATE, INSERT, and DELETE permissions for all tables in the SCHEMA to the user.
Synchronization object	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. Full synchronization does not support the following column types: bfile, xml, sdo_geometry, urowid, and user-defined types. Incremental synchronization does not support the following column types: bfile, xml, sdo_geometry, urowid, interval, and user-defined types. The maximum precision supported by timestamp and interval day to second is 6. During the incremental synchronization, if the source database is a physical standby Oracle database, data of the LOB type cannot be parsed (the data dictionary cannot be generated). If the table to be synchronized contains data of the LOB type, the incremental synchronization will fail. Full synchronization and structure migration do not support bitmap indexes, inverted indexes, and function indexes. During incremental synchronization, if the source or destination database is abnormal, the task fails. After the database is recovered, the task is globally started. The status of the original capture or replay component is ignored, and the replay component is started from the capture interruption point. For incremental synchronization, the LOB type supports only the BasicFiles attribute and does not support the SecureFiles attribute. The size of the LOB type must be less than 10 MB. For the TIMESTAMP WITH TIME ZONE data type, the value cannot be greater than 9999-12-31 23:59:59.999999 after being converted based on the time zone of the destination database. The default values of the source database can be to_date and sys_guid functions. To use other functions as default values, ensure that the destination database has the same functions. If the destination database does not have the corresponding function, the following results may be displayed: The default value may be left empty. The table fails to be created. As a result, the object comparison result is inconsistent or the task fails. If the table contains only LOB columns, data inconsistency may occur. If the empty function of the LOB type is used to write data in the Oracle database, the value queried through JDBC is an empty string. Whether the value is an empty string or NULL after being written to the destination database depends on the processing of the empty string in the destination database. For a table that does not have a primary key or index, the number of columns of non-large fields must be greater than 3. Otherwise, incremental synchronization may fail because all columns cannot be matched. Tables whose default values contain expressions of functions cannot be synchronized. Temporary tables in the source database cannot be synchronized. When you manually create a table structure, the time type in the destination database must be the same as that in the source database. Otherwise, time data may be inconsistent due to time zone conversion.
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. Only the following character sets are supported: ZHS16GBK, AL32UTF8, UTF8, US7ASCII, WE8MSWIN1252, WE8ISO8859P1, WE8ISO8859P2, WE8ISO8859P4, WE8ISO8859P5, WE8ISO8859P7, WE8ISO8859P9, WE8ISO8859P13, WE8ISO8859P15.
Destination database	The destination database must be a GaussDB primary/standby instance. 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	Cascading one-way synchronization is not supported. For example, data cannot be synchronized from instance A to instance B and then from instance B to instance C. 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. . The size of an Oracle archive log file must be greater than the maximum size of a single data record to prevent incremental data parsing exceptions caused by cross-file (more than two log files) of a single data record. If the Oracle character set is WE8MSWIN1252 or WE8ISO8859P1, the CLOB column synchronized to the destination database may contain garbled characters. You can change the character set of the source database to AL32UTF8 before the synchronization. If the PDB database is used for synchronization, all PDBs must be enabled during incremental synchronization. For an Oracle RAC cluster, use the scan IP address and service name to create a task. The SCAN IP address can provide better fault tolerance, load capability, and synchronization experience. If the source is an Oracle RAC database and the SCAN IP address is used to configure a DRS task, ensure that the SCAN IP address and DRS node IP address can communicate with all virtual IP addresses of the source database. Otherwise, the connectivity check fails. If the SCAN IP address is not used, the virtual IP address of a node can be used. In this case, DRS logs are parsed only on the RAC node specified by the virtual IP address. If the source is an RAC database, all RAC nodes must be online when incremental synchronization is started for the first time. Otherwise, an error occurs during incremental synchronization. If the source is an RAC database, the number of nodes cannot be increased or decreased during incremental synchronization to avoid incremental synchronization exceptions and ensure strong data consistency. The table without a primary key lacks a unique identifier for rows. When the network is unstable, you may need to retry the task several times, or data inconsistency may occur. 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 ZHS16GBK and the destination character set is UTF8, a Chinese character of ZHS16GBK 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. If you use DRS to synchronize table structures, the tables, constraints, and indexes in the same schema cannot have the same name with different letter cases. For example, table A contains an index named inx1, and table B contains an index name a. Table A and index a have the same name with different letter cases, which will cause table structure synchronization to fail. If multiple schemas are mapped to one schema, the source schemas cannot contain tables, constraints, and indexes with the same name but different letter cases. During synchronization, do not modify or delete the usernames, passwords, permissions, or ports of the source and destination databases. During the synchronization, do not perform the resetlogs operation on the source Oracle database. Otherwise, data cannot be synchronized and tasks cannot be restored. During synchronization, the rollback operation of the LOB type is not supported. Otherwise, the synchronization task fails. Do not write data to the destination database table during full synchronization. Otherwise, data will be inconsistent. 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. During table structure synchronization, if the destination database has a constraint with the same name as the source database, the table fails to be created. In a full synchronization for the table structure, the length of the char and varchar2 characters in the source database is automatically increased by at least 1.5 times by byte in the destination database (because the length of the destination database is in the unit of byte). The increase multiple depends on the character set of the source and destination databases. For example, if the character set is UTF8, increase the length (byte) by three times by default. If the character set is GBK, increase the length (byte) by two times by default. During full synchronization of the partitioned table structure, the table is converted to a non-partitioned table. During incremental synchronization, operations related to the partitioned table in the source database may fail to be executed in the destination database. When a table structure is fully synchronized, only default value constraints of the character string or number type are supported. Default value constraints of the function and sequence types are not supported. During an incremental synchronization, 0x00 at the end of BLOB and the spaces at the end of CLOB are truncated. During incremental synchronization, the following DDL operations are supported: Table-level synchronization supports alter table add column, alter table drop column, alter table rename column, alter table modify column, and truncate table. The modification of default values is not supported. Database-level synchronization supports create table. (Table definitions cannot contain functions.) During incremental synchronization, modify the start point of a capture task to resynchronize data. After the capture point is modified, the previous object-level comparison result is not displayed. If the start point of a capture task is changed separately, the change is synchronized to the start point of the replay task. That is, the start point of the replay task is the same as that of the capture task. This does not affect the change of the start point of the replay task. Full and incremental synchronization does not support the STRING extended data type (EXTENDED DATA TYPE) of Oracle 12c or later. Full and incremental synchronization does not support hidden columns (UNUSED, INVISIBLE). If the source database uses XStream for log reading, you need to insert data during incremental synchronization. Otherwise, the incremental synchronization delay keeps increasing. When DRS reads incremental Oracle logs in XStream mode, an Oracle XStream outbound is created on the source database. If another XStream outbound that reports an error already exists on the source database, the new XStream outbound created by DRS may be affected. As a result, data cannot be read. You can run the following command in the source database to check whether there are other XStream outbound errors: select o.server_name, c.capture_name, c.error_message from SYS.ALL_XSTREAM_OUTBOUND O, SYS.ALL_CAPTURE C where o.capture_name = c.capture_name When editing the task to add a new table, ensure that transactions of the new table have been committed. Otherwise, transactions that are not committed may fail to be synchronized to the destination database. You are advised to add tables during off-peak hours.

Procedure

On the Data Synchronization Management page, click Create Synchronization Task.

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 details

Figure 2 Synchronization instance details

**Table 4** Synchronization instance settings
Parameter	Description
Data Flow	Choose Self-built to self-built.
Source DB Engine	Select Oracle.
Destination DB Engine	Select GaussDB Primary/Standby.
Network Type	The public network is used as an example. Available options: Public network and VPN or Direct Connect
VPC	Select an available VPC.
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 ensure that there are available IP addresses. To ensure that the synchronization instance is successfully created, only subnets with DHCP enabled are displayed.
Security Group	Select a security group. You can use security group rules to allow or deny access to the instance.
Synchronization Mode	Available options: Full, Incremental, and Full+Incremental.
AZ	Select the AZ where you want to create the DRS instance. Selecting the one housing the source or destination database can provide better performance.

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.

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	The IP address or domain name of the source database. NOTE: For a RAC cluster, use a Scan IP address to improve access performance.
Port	The port of the source database. Range: 1 – 65535
Database Service Name	Enter a database service name (Service Name/SID). The client can connect to the Oracle database through the database service name. For details about how to query the database service name, see the prompt on the GUI.
PDB Name	Container database (CDB) and pluggable database (PDB) are new features in Oracle 12c and later versions. This function is optional, but it must be enabled if you want to migrate only PDB tables. Enter the service name, SID, username, and password of the CDB that contains the PDB tables to be migrated.
Database Username	The username for accessing the source database.
Database Password	The password for the database username.
SSL Connection	SSL encrypts the connections between the source and destination databases. If SSL is enabled, upload the SSL CA root certificate. NOTE: The maximum size of a single certificate file that can be uploaded is 500 KB. If SSL is not enabled, your data may be at risk.

Figure 5 Destination database information

**Table 7** Destination database settings
Parameter	Description
IP Address or Domain Name	IP address or domain name of the destination database in the IP address/Domain name:Port format. The port of the destination database. Range: 1 - 65535 You can enter up to 10 groups of IP addresses or domain names of the destination database. Separate multiple values with commas (,). Example: 192.168.0.1:8000,192.168.0.2:8000.
Database Username	The username for accessing the destination database.
Database Password	The password for the database username.

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
Flow Control	You can choose whether to control the flow. Yes You can customize the maximum migration speed. In addition, you can set the time range based on your service requirements. The traffic rate setting usually includes setting of a rate limiting time period and a traffic rate value. Flow can be controlled all day or during specific time ranges. The default value is All day. A maximum of three time ranges can be set, and they cannot overlap. The flow rate must be set based on the service scenario and cannot exceed 9,999 MB/s. Figure 7 Flow control No The synchronization speed is not limited and the outbound bandwidth of the source database is maximally used, which will increase the read burden on the source database. For example, if the outbound bandwidth of the source database is 100 MB/s and 80% bandwidth is used, the I/O consumption on the source database is 80 MB/s. NOTE: The flow control mode takes effect only in the full synchronization phase. You can also change the flow control mode after creating a task. For details, see Modifying the Flow Control Mode.
Synchronization Object	The left pane displays the source database objects, and the right pane displays the selected objects. You can select Tables, Import object file, or Databases for Synchronization Object as required. 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. For details about how to import an object file, see Importing Synchronization Objects. 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.

On the Advanced Settings page, view the parameters you set for full synchronization or incremental synchronization in 2. The default parameter values cannot be modified. Click Next.

Figure 8 Full synchronization

**Table 9** Full synchronization settings
Parameter	Description	Default Value
Synchronization Object Type	Available options: Table structure, Data, and Constraint Data is mandatory.	All options
Stream Mode	In this mode, data is written to the destination database by shard. Data is submitted once for each shard. Otherwise, The data is submitted once every 16 MB of data is written to the destination database.	Enabled
Concurrent Export Tasks	The number of threads that can be started to export data from the Oracle database.	8
Concurrent Import Tasks	The number of threads that can be started to concurrently write data to GaussDB.	8
Import Mode	COPY With the COPY interface, writing efficiency is relatively high, but task errors may occur due to data conflicts. INSERT Writing data using the INSERT statement can avoid data conflicts but the writing efficiency is low.	COPY
Rows per Shard	Export tables in shards to improve the efficiency of real-time synchronization. 0 All tables are not sharded, and each table is synchronized as a whole. Other values The table is sharded based on the specified value (or the primary key column). If the number of records in a table is less than the value of this parameter, the table is not sharded. If the table is a partitioned table, each partition is synchronized as a shard instead of being sharded based on the value you set. If a table has no primary key or unique index, the table is not sharded. In this case, this parameter is meaningless. If a table is not analyzed in a timely manner, the value of NUM_ROWS in the ALL_TABLES view is empty, and the table is not sharded.	520000
Synchronization Point	Set this parameter to the current system change number (SCN). If you set this parameter to a future SCN or the SCN range where deleted archive logs are located, the task will fail.	The default value is the SCN generated when the task is started.

Figure 9 Incremental synchronization

**Table 10** Incremental synchronization settings
Parameter	Description	Default Value
Concurrent Log Capture Tasks	The number of concurrent threads for reading Oracle logs. The value ranges from 1 to 16.	1
Capture Start Point	Specifies the SCN for starting the capture. SCNs are designed to meet service requirements. It consists of a start SCN for capturing and a valid SCN. For details, see the SCN concepts of Oracle.	If this parameter is left blank, the current SCN of the database is used as the start point by default.
Concurrent Replay Tasks	The number of concurrent threads for writing data to the destination database. The value ranges from 1 to 64.	64
Replay Policy	Automated After the task is started, the replay component is started automatically. Manual After a task is started, the replay component needs to be started manually.	Auto
Conflict Policy	Overwrite The data captured by DRS will overwrite the data in the destination database. Report error An error message is displayed, indicating that the synchronization task is abnormal. Ignore The system skips the error record and continues the data replay.	Overwrite
Replay Start Point	Specifies the SCN where the replay starts.	If this parameter is not specified, the replay start point is the same as the capture start point by default.

On the Process Data page, set the filtering rules for data processing.
- If data processing is not required, click Next.
- If you need process columns or filter out data, set the corresponding rules by referring to Processing Data.
Figure 10 Processing data
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 11 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.

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 12 Task startup settings

**Table 11** 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.

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.