Migrate data from a PostgreSQL database to OceanBase Database Community Edition

This topic describes how to use OceanBase Migration Service (OMS) Community Edition to migrate data from a PostgreSQL database to OceanBase Database Community Edition.

Background information

OMS Community Edition allows you to create a task to migrate the existing business data and incremental data from a PostgreSQL database to OceanBase Database Community Edition through schema migration, full migration, and incremental synchronization.

PostgreSQL databases in the following modes are supported as the sources: primary database only, standby database only, and primary/standby databases. The following table describes the data migration operations supported by each mode.

Prerequisites

• You have created a corresponding schema in the target database. OMS Community Edition allows you to migrate tables and columns. You must create a corresponding schema in the target database before the migration.

• You have created dedicated database users for data migration in the source PostgreSQL database and OceanBase Database Community Edition that serves as the target, and granted required privileges to the users. For more information, see Create a database user.

Limitations

• Take note of the following limitations on the source database:

  Do not perform DDL operations that modify database or table schemas during schema migration or full migration. Otherwise, the data migration task may be interrupted.

• At present, PostgreSQL 10.x, 11.x, 12.x, 13.x, 14.x, 15.x, and 16.x are supported.

• OMS Community Edition allows you to migrate tables with or without a primary key and tables with non-null unique keys from a PostgreSQL database to OceanBase Database Community Edition.

• When you use OMS Community Edition to migrate data from a PostgreSQL database to OceanBase Database Community Edition, DDL synchronization is not supported.

• If the target is a database, OMS Community Edition does not support triggers in the target database. If triggers exist in the target database, the data migration may fail.

• When you migrate partitioned tables from a PostgreSQL database, take note of the following limitations:

  • The parent table and child table must have the same schema.

  • The parent table and child table must have the same primary key columns, NOT NULL unique key columns, and partitioning columns, or the primary key columns or NOT NULL unique key columns must include the partitioning columns.

  • The primary keys or NOT NULL unique keys must be unique in the parent table.

• The REPLICA IDENTITY parameter must be set to FULL for all parent tables and child tables to be migrated from the PostgreSQL database.

  • If the REPLICA IDENTITY parameter is not set to FULL, the operation to update or delete the business data may fail.

  • If you use a wildcard to specify the migration objects, the PostgreSQL database must subscribe to all tables in the selected database, including the selected tables, unselected tables, and new tables. The REPLICA IDENTITY parameter must be set to FULL for all tables. Otherwise, the operation to update or delete the business data may fail.

• OMS Community Edition does not support the migration of unlogged tables and temporary tables from the PostgreSQL database.

• The data source identifiers and user accounts must be globally unique in OMS Community Edition.

• OMS Community Edition supports the migration of only objects whose database name, table name, and column name are ASCII-encoded without special characters. The special characters are line breaks and | " ' ` ( ) = ; / &.

Considerations

• Data source identifiers and user accounts must be globally unique in OMS Community Edition.

• OMS Community Edition only supports migrating databases, tables, and column objects with ASCII-compliant names that do not contain special characters (spaces, |"'`()=;/&).

Considerations

* Data source identifiers and user accounts must be globally unique in OMS Community Edition.

* OMS Community Edition only supports migrating databases, tables, and column objects with ASCII-compliant names that do not contain special characters (spaces, |"'`()=;/&).

* OceanBase Community Edition does not support specifying array indexes, whereas PostgreSQL does. The format for specifying array indexes in PostgreSQL is `[start index: number of elements]={x,x,x,x}`.

For example, if the array indexes specified in PostgreSQL are `[-1:10]={0,0,0,100,101,102,NULL,NULL,NULL,NULL,NULL,200}`, they are written to OceanBase Community Edition as `{0,0,0,100,101,102,NULL,NULL,NULL,NULL,NULL,200}`. When data is written from OceanBase Community Edition to PostgreSQL, the index values are reset to 1. This poses a problem if your application depends on specific index values.

* An error is returned when an item in a character array contains a line break.

* PostgreSQL supports multidimensional arrays. For example, a VARCHAR(255)[] data type can store multidimensional array data when you write data to it:

Considerations

• To ensure the performance of a data migration task, we recommend that you migrate no more than 1,000 tables at a time.

• If a source table does not have a primary key or all columns of the table have a non-null unique key, duplicate data may exist during migration to the target database.

• In a reverse incremental synchronization scenario, if data migration is performed in full-column matching mode for UPDATE and DELETE operations, the following issues may occur:

  • Poor performance

    Due to the absence of primary key indexes, each UPDATE or DELETE operation is performed after a full-table scan.

  • Data inconsistency

    The LIMIT syntax is not supported for UPDATE and DELETE operations in PostgreSQL databases. Therefore, if multiple data records are matched in full-column matching mode, the data in the source database may be more than that in the target database after UPDATE or DELETE operations. Assume that the t1 table without a primary key has two columns: c1 and c2. Two data records where c1 = 1 and c2 = 2 exist in the source table. When you delete only one data record from the source table based on the where c1 = 1 and c2 = 2 condition, the two data records that match the condition in the target table will be deleted accordingly, causing data inconsistency between the source and target tables.

• In reverse incremental synchronization from a PostgreSQL database to OceanBase Database Community Edition of a version earlier than V3.2.x, if a source table is a multi-partition table with a global unique index and the values of the partitioning key of the table are updated, data can be lost during the migration.

• If you change the unique index in the target database, you must restart the Incr-Sync component. Otherwise, the data may be inconsistent.

• If the clocks between nodes or between the client and the server are out of synchronization, the latency may be inaccurate during incremental synchronization or reverse incremental synchronization.

  For example, if the clock is earlier than the standard time, the latency can be negative. If the clock is later than the standard time, the latency can be positive.

• Take note of the following considerations if you want to perform data merge migration:

  • We recommend that you configure the mappings between the source and target databases by importing objects or specifying matching rules.

  • We recommend that you manually create schemas in the target database. If you use OMS Community Edition to create schemas, skip failed objects in the schema migration step.

• A difference between the source and target table schemas may result in data consistency. Some known scenarios are described as follows:

  • When you manually create a table schema, if the data type of a column in the source is not supported by OMS Community Edition, implicit data type conversion may occur, which causes inconsistent column types between the source and target databases.

  • If the length of a column in the target database is shorter than that in the source database, the data of this column may be automatically truncated, which causes data inconsistency between the source and target databases.

• If you select only Incremental Synchronization when you create the data migration task, OMS Community Edition requires that the local incremental logs in the source database be retained for more than 48 hours.

  ​​​If you select Full Migration and Incremental Synchronization when you create the data migration task, OMS Community Edition requires that the local incremental logs of the source database be retained for at least seven days. Otherwise, the data migration task may fail or the data in the source and target databases may be inconsistent because OMS Community Edition cannot obtain incremental logs.

Data type mappings

Procedure

1. Create a data migration task.

   1. Log in to the console of OMS Community Edition.

   2. In the left-side navigation pane, click Data Migration.

   3. On the Data Migration page, click New Task in the upper-right corner.

2. On the Select Source and Target page, configure the parameters.

   Parameter	Description
   Data Migration Task Name	We recommend that you set it to a combination of digits and letters. It must not contain any spaces and cannot exceed 64 characters in length.
   Tag	Click the field and select a tag from the drop-down list. You can also click Manage Tags to create, modify, and delete tags. For more information, see Use tags to manage data migration tasks.
   Source	If you have created a PostgreSQL data source, select it from the drop-down list. If not, click New Data Source in the drop-down list and create one in the dialog box that appears on the right. For more information, see Create a PostgreSQL data source. You can select a PostgreSQL data source in primary database only mode or primary/standby databases mode. This topic describes how to create a data migration task with a PostgreSQL data source in primary/standby databases mode.
   Target	If you have created an OceanBase-CE data source, select it from the drop-down list. If not, click New Data Source in the drop-down list and create one in the dialog box that appears on the right. For more information about the parameters, see Create an OceanBase-CE data source.
   Scenario Type	Valid values: Tables with Unique Key and All Tables. ​If a table has a primary key or non-null unique key, this table is a table with a unique key. If you select All Tables, tables with a primary key or a unique key and those without a unique key, except for temporary tables, are included.

3. Click Next.

   If you have selected Tables with Unique Key for Scenario Type, click OK in the dialog box that appears.

4. On the Select Migration Type page, configure the parameters.

   Options for Migration Type are Schema Migration, Full Migration, Incremental Synchronization, Full Verification, and Reverse Incremental Migration.

   Migration type	Description
   Schema migration	The definitions of data objects, such as tables, indexes, constraints, comments, and views, are migrated from the source database to the target database. Temporary tables are automatically filtered out.
   Full migration	After a full migration task is started, OMS Community Edition migrates existing data of tables in the source database to corresponding tables in the target database. If you select Full Migration, we recommend that you use the ANALYZE statement to collect the statistics of the PostgreSQL database before data migration.
   Incremental synchronization	Changed data in the source database is synchronized to the corresponding tables in the target database after an incremental synchronization task starts. Data changes are data addition, modification, and deletion. Options for DML Synchronization in the Incremental Synchronization section include Insert, Delete, and Update. You can select the operations as needed. For more information, see DML filtering. OMS automatically creates publications and slots for incremental synchronization from a PostgreSQL database. However, you need to monitor the usage of the disk for storing archive files. By default, OMS Community Edition instructs the database to update the confirmed_flush_lsn value of a slot every 10 minutes. The interval can be customized. By default, archive files need to be retained for 48 hours. Therefore, OMS instructs the database to clean up only archive logs that have been retained for more than 48 hours. The retention period can be customized. If the archive logs cannot be cleared during the migration because slots exist, you need to destroy the data migration task and then clear the archive logs.
   Full verification	If you select Full Verification, we recommend that you collect the statistics of both the source and target databases before full verification. For more information about how to collect statistics of OceanBase Database Community Edition, see Manual statistics collection. If you select Incremental Synchronization but do not select all DML operations in the DML Synchronization section, you cannot select Full Verification. OMS Community Edition supports full verification only for tables with a primary key or a non-null unique key.
   Reverse incremental migration	When a reverse incremental migration task starts, OMS migrates the data changed in the target database after the business switchover back to the source database in real time. You cannot select Reverse Incremental Migration in the following cases: Data merge migration that involves multiple tables is enabled. Multiple source schemas map to the same target schema.

5. (Optional) Click Next. If you have selected Reverse Incremental Migration but the ConfigUrl or the username or password of the Data Replication Center (DRC) user is not configured for the target OceanBase-CE data source, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information about the parameters, see Create an OceanBase-CE data source.

   After you configure the parameters, click Test Connectivity. After the test succeeds, click Save.

6. Click Next. On the Select Migration Objects page, select the migration objects and migration scope.

   You can select Specify Objects or Match Rules to specify the migration objects. The following procedure describes how to specify migration objects by using the Specify Objects option. For information about the procedure for specifying migration objects by using the Match Rules option, see Configure matching rules for migration objects.

   Notice

   • The name of a table to be migrated, as well as the names of columns in the table, must not contain Chinese characters.

   • If a database or table name contains double dollar signs ("$$"), you cannot create the migration task.

   

   1. In the Select Migration Objects section, select Specify Objects.

   2. In the Specify Migration Scope section, select the objects to be migrated from the Source Object(s) list. You can select tables and views of one or more databases as the migration objects.

   3. Click > to add the selected objects to the Target Object(s) list.

   When you migrate data from a PostgreSQL database to OceanBase Database Community Edition, OMS Community Edition allows you to import objects from text, rename objects, set row filters, view column information, and remove a single migration object or all migration objects.

   Operation	Description
   Import objects	In the list on the right of the Specify Migration Scope section, click Import Objects in the upper-right corner. In the dialog box that appears, click OK. Notice This operation will overwrite previous selections. Proceed with caution. In the Import Objects dialog box, import the objects to be migrated. You can import CSV files to rename databases/tables and set row filtering conditions. For more information, see Download and import the settings of migration objects. Click Validate. After the validation succeeds, click OK.
   Rename objects	OMS Community Edition allows you to rename migration objects. For more information, see Rename a database table.
   Configure settings	OMS Community Edition allows you to filter rows by using WHERE conditions. For more information, see Use SQL conditions to filter data. You can also view column information of the migration objects in the View Column section.
   Remove one or all objects	OMS Community Edition allows you to remove a single object or all objects to be migrated to the target database during data mapping. To remove a single migration object: In the list on the right of the Specify Migration Scope section, move the pointer over the target object and click Remove. To remove all migration objects: In the list on the right of the Specify Migration Scope section, click Remove All in the upper-right corner. In the dialog box that appears, click OK.

7. Click Next. On the Migration Type page, configure the parameters.

   To view or modify parameters of the Full-Import or Incr-Sync component, click Configuration Details in the upper-right corner of the Full Migration or Incremental Synchronization section. For more information about the parameters, see Component parameters.

   • Full migration

     The following parameters are displayed only if you have selected Full Migration on the Select Migration Type page.

     Parameter	Description
     Concurrency Speed	Valid values: Stable, Normal, Fast, and Custom. The amount of resources to be consumed by a full migration task varies based on the migration performance. If you select Custom, you can set Read Concurrency, Write Concurrency, and JVM Memory as needed.
     Processing Strategy When Target Table Has Records	Valid values: Ignore and Stop Migration. If you select Ignore, when the data to be inserted conflicts with the existing data of a target table, OMS Community Edition retains the existing data and records the conflict data. Notice If you select Ignore, data is pulled in IN mode for full verification. In this case, the scenario where the target contains more data than the source cannot be verified, and the verification efficiency will be decreased. If you select Stop Migration and a target table contains data, an error is returned during full migration, indicating that the migration is not allowed. In this case, you must clear the data in the target table before you can continue with the migration. Notice After an error is returned, if you click Resume in the dialog box, OMS Community Edition ignores this error and continues to migrate data. Proceed with caution.
     Writing Method	Valid values: SQL (specifies to write data to tables by using INSERT or REPLACE) and Direct Load (specifies to write data through direct load). For more information about the direct load method, see Direct load.
     Post-Indexing	Specifies whether to create indexes after the full migration is completed. Post-indexing can shorten the time required for full migration. For more information about the considerations on post-indexing, see the description below. Notice This feature is supported only if you have selected both Schema Migration and Full Migration on the Select Migration Type page.

     If post-indexing is allowed, we recommend that you adjust the parameters based on the hardware conditions of the target database and the business traffic.

     • If you use OceanBase Database Community Edition V4.x, adjust the following parameters of the sys tenant and business tenants by using a command-line interface (CLI) client.

       • Adjust the parameters of the sys tenant

         // parallel_servers_target specifies the queuing conditions for parallel queries on each server.
         // To maximize performance, we recommend that you set this parameter to a value greater than, for example, 1.5 times, the number of physical CPU cores. In addition, make sure that the value does not exceed 64, to prevent database kernels from contending for locks.
         set global parallel_servers_target = 64; 
         

       • Adjust the parameters of a business tenant

         // Specify the limit on the file memory buffer size.
         alter system set _temporary_file_io_area_size = '10' tenant = 'xxx'; 
         // Disable throttling in V4.x.
         alter system set sys_bkgd_net_percentage = 100;  
         

     • If you use OceanBase Database Community Edition V3.x, adjust the following parameters of the sys tenant by using a CLI client.

       // parallel_servers_target specifies the queuing conditions for parallel queries on each server.
       // To maximize performance, we recommend that you set this parameter to a value greater than, for example, 1.5 times, the number of physical CPU cores. In addition, make sure that the value does not exceed 64, to prevent database kernels from contending for locks.
       set global parallel_servers_target = 64; 
       // `data_copy_concurrency` specifies the maximum number of concurrent data migration and replication tasks allowed in the system.
       alter system set data_copy_concurrency = 200; 
       

   • Incremental synchronization

     The following parameters are displayed only if you have selected Incremental Synchronization on the Select Migration Type page.

     Parameter	Description
     Concurrency Speed	Valid values: Stable, Normal, Fast, and Custom. The amount of resources to be consumed by an incremental synchronization task varies based on the synchronization performance. If you select Custom, you can set Read Concurrency, Write Concurrency, and JVM Memory as needed.
     Incremental Synchronization Start Timestamp	If you have set the migration type to Full Migration, this parameter is not displayed. If you have selected Incremental Synchronization but not Full Migration, specify a point in time after which the data is to be synchronized. The default value is the current system time. For more information, see Set an incremental synchronization timestamp.
     Incremental Record Retention Time	The duration that incremental parsed files are cached in OMS Community Edition. A longer retention period results in more disk space occupied by the Store component of OMS Community Edition.

   • Full verification

     The following parameters are displayed only if you have selected Full Verification on the Select Migration Type page.

     Parameter	Description
     Concurrency Speed	Valid values: Stable, Normal, Fast, and Custom. Through resource configuration for the Full-Verification component, you can limit the resource consumption of a task in the full verification phase. If you select Custom, you can set Read Concurrency, Write Concurrency, and JVM Memory as needed.

8. Click Precheck to start a precheck on the data migration task.

   During the precheck, OMS Community Edition checks the read and write privileges of the database users and the network connectivity of the databases. A data migration task can be started only after it passes all check items. If an error is returned during the precheck, you can perform the following operations:

   • Identify and troubleshoot the problem and then perform the precheck again.

   • Click Skip in the Actions column of the failed precheck item. In the dialog box that prompts the consequences of the operation, click OK.

9. Click Start Task. If you do not need to start the task now, click Save to go to the details page of the task. You can start the task later as needed.

   OMS Community Edition allows you to modify the migration objects when the data migration task is running. For more information, see View and modify migration objects. After the data migration task is started, it is executed based on the selected migration types. For more information, see the Migration Details section in the View details of a data migration task topic.

References

• Create a PostgreSQL data source

• Create an OceanBase-CE data source

• Component parameters

• View and modify migration objects

• View details of a data migration task