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PolarDB for Oracle Migration Synchronization to PolarDB PostgreSQL

Use this page to replicate data from PolarDB for Oracle to PolarDB PostgreSQL in NineData. The link supports schema, full, and incremental replication.

Before you begin​

  • The source and target data sources have been added to NineData. For details, see Add Data Source.

  • The source data source is Alibaba Cloud PolarDB for Oracle.

  • The target data source is Alibaba Cloud PolarDB PostgreSQL V2.0.

  • As described in Alibaba Cloud documentation, before NineData connects directly to PolarDB for Oracle, add the NineData service addresses to the source cluster allowlist. When you connect to the target PolarDB PostgreSQL instance, make sure access from NineData is also allowed on the target side. For details, see the Alibaba Cloud document Set IP address whitelists for a cluster.

  • You must have the following permissions on the source and target data sources:

    Replication Type
    		Source Data SourceTarget Data Source
    Schema ReplicationCONNECT, USAGE (schema), SELECT (system catalogs)CONNECT, CREATE (schema), DDL (CREATE / ALTER / DROP)
    Full ReplicationCONNECT, USAGE (schema), SELECT (source tables)CONNECT, USAGE (schema), table privileges (CREATE, ALTER, DROP, SELECT, INSERT, UPDATE, DELETE)
    Incremental ReplicationREPLICATION or SUPERUSERCONNECT, USAGE (schema), table privileges (ALTER, DROP, SELECT, INSERT, UPDATE, DELETE)

  • For incremental replication, confirm the following parameters on the Alibaba Cloud cluster parameter page instead of editing instance files directly. For parameter details, see the Alibaba Cloud document Default values of cluster parameters.

    • wal_level=logical
    • max_replication_slots > 1
    • max_wal_senders > 1
    • Set wal_sender_timeout to 0 to avoid timeout interruptions on replication connections

Limitations​

  • Before starting replication, evaluate the performance of the source and target data sources and run the task during off-peak hours whenever possible. Otherwise, full initialization can consume read and write resources on both sides and increase database load.
  • Make sure each synchronized table has a primary key or unique constraint, and that column names are unique. Otherwise, duplicate data can be replicated.

Procedure​

  1. Sign in to the NineData Console.

  2. In the left navigation pane, click Replication > Data Replication.

  3. On the Replication page, click Create Replication.

  4. On the Source & Target tab, configure the fields in the table, and click Next.

    Parameter
    		Description
    NameEnter a name for the data synchronization task. To make the task easier to find and manage later, use a meaningful name. Up to 64 characters are supported.
    SourceThe data source that contains the objects to synchronize.
    Datahub ProjectSelect the target Datahub Project. Data from the source data source will be written to the specified Project.
    TypeSelect the replication type.
    • Schema: Synchronize only the database and table schemas of the source data source, without synchronizing data.
    • Full: Synchronize all objects and data from the source data source, namely full data replication. The switch on the right enables periodic full replication. For more information, see Periodic Full Replication.
    • Incremental: After full synchronization completes, perform incremental synchronization based on the logs of the source data source.
    Incremental StartedRequired only when Type is Incremental.
    • From Started: Use the current replication task start time as the baseline for incremental replication.
    • Customized Time: Select the point in time from which incremental replication starts. Select a time zone based on the region of your business. If the configured time point is earlier than the current replication task start time and DDL operations occurred during that period, the replication task will fail.
    Spec (Unavailable only when Schema is selected)The specification of the replication task. A larger specification provides a higher replication rate. Hover over the details icon to view the rate and configuration information of each specification. Each specification shows the available quantity and total quantity. When the available quantity is 0, the specification is grayed out and cannot be selected.
    If target table already exists (Required when Schema is selected)
    • Pre-Check Error and Stop Task: Stop the task when a table with the same name is detected during the precheck stage.
    • Skip and Continue Task: When a table with the same name is detected during the precheck stage, display a message and continue the task. During schema replication, ignore the table with the same name. If you also perform data replication, data is appended to the table with the same name and existing data is not overwritten.
    • Delete Objects and Rewrite: When a table with the same name is detected during the precheck stage, display a message and continue the task. During schema replication, delete the table with the same name in the target database and replicate the table schema again based on the source database. If you also perform data replication, data is written after schema replication completes.
    Target Table Exists Data (Required when Full is selected)
    • Pre-Check Error and Stop Task: Stop the task when data is detected in the target table during the precheck stage.
    • Ignore existing target data and append to it.: When data is detected in the target table during the precheck stage, ignore that data and append other data.
    • Clear target existing data before write: When data is detected in the target table during the precheck stage, delete that data and write it again.
    Incremental data conflict handling strategy for target table (Required when Incremental is selected)
    • Runtime error: During incremental replication, report an error when target data already exists and wait for manual intervention.
    • Do not update target data: During incremental replication, do not write data when target data already exists, and continue subsequent tasks.
    • Update target data: During incremental replication, overwrite the target data when target data already exists.

  5. On the Objects tab, configure the parameters in the table, and click Next.

    Parameter
    		Description

    To create multiple replication tasks with the same replication objects, import a configuration file. Click Import Config, click Download Template to download the template, edit the file, and then click Upload to upload it and import the objects in bulk. The configuration file uses these fields:

    Parameter
    		Description
    source_table_nameThe source table name of the object to synchronize.
    destination_table_nameThe target table name that receives the synchronized object.
    source_schema_nameThe source schema name of the object to synchronize.
    destination_schema_nameThe target schema name that receives the synchronized object.
    source_database_nameThe source database name of the object to synchronize.
    target_database_nameThe target database name that receives the synchronized object.
    column_listThe list of columns to synchronize.
    extra_configurationAdditional configuration information. This field supports:
    • column_rules: Defines column mappings and value rules. Field descriptions:
      • column_name: Original column name.
      • destination_column_name: Specifies the target column name.
      • column_value: Specifies the column value, which can be an SQL function or a constant value.
    • filter_condition: Specifies row-level data filtering conditions. Only rows that meet the conditions are replicated.
    tip

    • Example of extra_configuration:

      {
        "extra_config":{
          "column_rules":[
            {
               "column_name": "created_time",
               "destination_column_name": "migrated_time",
               "column_value": "current_timestamp()"
            }
          ],
           "filter_condition": "id != 0"
        }
      }

      In this example, created_time is mapped to migrated_time, the target column value is changed to current_timestamp(), and only rows whose id value is not 0 are synchronized.

    • For a complete example of the configuration file, see the downloaded template.

  6. On the "Mapping" tab, configure the mapping that matches the selected replication type, then click Save and Pre-Check. If source or target metadata changes while you configure mappings, click Refresh Metadata to refresh the metadata.

    • Includes Schema: Configure the table name after synchronization to the target data source.

    • Does not include Schema: NineData selects the database with the same name in the target data source by default. If no such database exists, select the target database manually. The table names and column names in the target database must match the synchronization objects. If they do not match, map the table names and column names manually.

    Other available actions:

    • Click Mapping & Filtering to customize the column names after synchronization to the target data source.
    • On the Mapping & Filtering page, click Data Filter to configure filtering conditions by using comparison expressions. Only data that meets the filtering conditions is synchronized to the target data source. For example, if the filtering condition is set to emp_no>=10005, data whose emp_no column value is less than 10005 is not synchronized to the target data source.
    • Click the replace_tablename icon to the right of "Target Table" to search for a table name and replace it with the target name.
    • Enter a table name in the Search Table text box to quickly locate the target table.
    • Click Batch Configuration to define common rules in batches, such as table name and column name case conversion, prefix or suffix addition, and replacement. Use this option to apply mapping configuration to many tables and columns at the same time.
  • Click the drop-down menu to the right of Object Owner to specify the owner of the object. If you do not select an owner, An account with the same name as schema is used by default.

Other available actions:

  • Select Mapping & Filtering to customize target column names after synchronization.
  • On the Mapping & Filtering page, enter a comparison expression in the text box below Data Filter as the filtering condition. Only data that meets the filtering condition is synchronized to the target data source. For example, if the filtering condition is emp_no>=10005, data whose emp_no column value is less than 10005 is not synchronized to the target data source.
  • Select the replace_tablename icon next to "Target Table" to search for table names and replace them with target names.
  • Enter a table name in the Search Table text box to quickly locate the target table.
  • Select Batch Configuration to define common rules in batches, such as table or column name case conversion, prefix or suffix addition, and replacement. Use batch rules to apply consistent mapping to a large number of tables and columns.

  1. On the Pre-check tab, wait for NineData to complete the precheck. After the precheck passes, click Launch.

    • Select Enable data consistency comparison to start a data consistency comparison task based on the source data source after synchronization completes. Based on the selected Type, Enable data consistency comparison starts at these times:

      • Schema: Starts after schema replication completes.
      • Schema+Full: Starts after full replication completes.
      • Full: Starts after full replication completes.
      • Schema+Full+Incremental, Incremental: Starts when incremental data is consistent with the source data source for the first time and Delay is 0 seconds. Click View Details to view synchronization delay on the Details page. sync_delay

    • If the precheck fails, click Details in the Actions column for the failed check item, review the cause, fix the issue, and then click Check Again to run the precheck again until it passes.

    • Items with Warning in Result can be fixed or ignored if required.

  2. On the Launch page, the Launch Successfully message appears, indicating that the synchronization task has started. Then perform these actions:

    • Click View Details to view the execution status of each stage of the synchronization task.
    • Click Back to list to return to the Replication task list page.

Results​

  1. Sign in to the NineData Console.

  2. In the navigation menu, select Replication > Data Replication.

  3. On the Replication page, click the Task ID of the target synchronization task. The task details page shows the following information.

    result

    Number
    		Function
    		Description
    1Sync DelayThe synchronization delay between the source and target data sources. 0 seconds means the target has caught up with the source. Switch traffic based on your migration plan.
    2Configure AlertsWhen the task fails, NineData notifies the selected channel through the configured alert.
    3More
    • Pause: Pause the task. Only tasks with Running status are selectable.
    • Duplicate: Create a new replication task with the same configuration as the current task.
    • Terminate: Terminate tasks that are incomplete or still listening (that is, in incremental synchronization). After a task is terminated, it cannot be restarted, so proceed with caution. If the synchronization objects contain triggers, trigger replication options appear for selection.
    • Delete: Delete the task. Once deleted, it cannot be recovered, so proceed with caution.
    4Structure Replication (displayed in scenarios involving structure replication)Displays the progress and detailed information of structure replication.
    • Select Log to view the execution logs of structure replication.
    • Select the refresh to view the latest information.
    • Select View DDL in the Actions column for the target object in the list to view SQL replay.
    5Full Replication (displayed in scenarios involving full replication)Displays the progress and detailed information of full replication.
    • Select Monitor to view various monitoring indicators during full replication. During full replication, select Flow Control Settings on the monitoring page to limit the rate of writing to the target data source per second. The unit is rows/second.
    • Select Log to view the execution logs of full replication.
    • Select the refresh to view the latest information.
    6Incremental Replication (displayed in scenarios involving incremental replication)Displays incremental replication indicators.
    • Select View Threads to view the operations currently being executed by the current replication task, including:
      • Thread ID: Replication tasks are executed in multiple threads, and this shows the current thread number.
      • Execute SQL: Details of the SQL statement currently being executed by the current thread.
      • Response Time: The response time of the current thread. If this value increases, it indicates that the current thread may be stuck for some reason.
      • Event Time: The timestamp when the current thread was started.
      • Status: The status of the current thread.
    • Select Flow Control Settings to limit the rate of writing to the target data source per second. The unit is rows/second.
    • Select Log to view the execution logs of incremental replication.
    • Select the refresh to view the latest information.
    7Modify ObjectDisplays the modification records of synchronization objects.
    • Select Modify Objects to configure the synchronization objects.
    • Select the refresh to view the latest information.
    8Data ComparisonDisplays the comparison results between the source and target data sources. If data comparison is not enabled, select Enable Comparison on the page to enable it.
    • Select Re-compare to rerun the comparison for the current source and target data sources.
    • Select Stop to stop the comparison task immediately after it starts.
    • Select Log to view the execution logs of consistency comparison.
    • Select Monitor (displayed only in data comparison) to view the trend chart of RPS (records per second) comparison. Select Details to view earlier records.
    • Select the details in the Actions column in the comparison list (displayed under the Data tab only when inconsistencies are found) to view details of the comparison between the source and target data sources.
    • Select the sql in the Actions column in the comparison list (displayed only when inconsistencies are found): Generate change SQL. Copy this SQL to the target data source and run it to fix the mismatch.
    9ExpandDisplays detailed information of the current replication task. Common actions:
    • Export table configuration: Export the current task's database and table configuration for quick import when creating another replication task with the same objects.
    • Alert Rules: Configure alerts for the current task.

Appendix: Pre-Check Item List​

Check ItemCheck Content
Target database permission checkCheck whether the target account has the required permissions
Target database same-name object existence checkCheck whether objects with the same name already exist in the target database
Source data source connection checkCheck the gateway status of the source data source, whether the instance is reachable, and whether the username and password are correct
Target data source connection checkCheck the gateway status of the target data source, whether the instance is reachable, and whether the username and password are correct
Source database permission checkCheck whether the source account has the required permissions
Source and target version checkCheck whether the source and target versions are compatible
Target database data existence checkCheck whether data already exists in the target objects to be synchronized
Cyclic replication checkCheck whether a replication loop exists
Source configuration checkCheck whether the source configuration is ready for incremental log reading
Target read-only status checkCheck whether the target database instance is read-only