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 data 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.
| Mode | Supported operation |
|---|---|
| Primary database only | Schema migration, full data migration, incremental synchronization, full verification, and reverse incremental migration |
| Standby database only | Schema migration, full data migration, and full verification |
| Primary/Standby databases | Primary database: incremental synchronization and reverse incremental migration Standby database: schema migration, full data migration, and full verification |
Prerequisites
You have created a corresponding schema in OceanBase Database Community Edition that serves as the destination. OMS Community Edition allows you to migrate tables and columns. You must create a corresponding schema in the destination 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 destination, and granted corresponding privileges to the users. For more information, see Create a database user.
Limitations
Limitations on the source database
Do not perform DDL operations that modify database or table schemas during schema migration or full data 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 primary keys and tables with NOT 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 destination is a database, OMS Community Edition does not support triggers in the destination database. If triggers exist in the destination database, the data migration may fail.
When you migrate partitioned tables from a PostgreSQL database, take note of the following limits:
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 key columns, or the primary key columns or NOT NULL unique key columns must include the partitioning key columns.
The primary keys or NOT NULL unique keys must be unique in the parent table.
REPLICA IDENTITYmust be set to FULL for all parent tables and child tables to be migrated from the PostgreSQL database.If
REPLICA IDENTITYis 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.
REPLICA IDENTITYmust be set to FULL for all parent 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 in 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
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 NOT NULL unique key, duplicate data may exist during migration to the destination.
In a reverse incremental migration 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 at the source may be more than that at the destination 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 at the source. When you delete only one data record from the source based on the
where c1 = 1 and c2 = 2condition, the two data records that match the condition at the destination will be deleted accordingly, causing data inconsistency between the source and the destination.
In reverse incremental migration 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 of the destination, 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 migration.
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 destination databases by importing objects or specifying matching rules.
We recommend that you manually create schemas at the destination. If you use OMS Community Edition to create schemas, skip failed objects in the schema migration step.
A difference between the source and destination 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 destination.
If the length of a column at the destination is shorter than that at the source, the data of this column may be automatically truncated, which causes data inconsistency between the source and destination.
If you select only 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 more than 48 hours.
If you select Full Data 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 7 days. Otherwise, the data migration task may fail or the data in the source and destination databases may be inconsistent because OMS Community Edition cannot obtain incremental logs.
Data type mappings
| PostgreSQL database | OceanBase Database Community Edition |
|---|---|
| bigint | BIGINT |
| bigserial | BIGINT |
| bit [(n)] | BIT |
| Boolean | TINYINT(1) |
| box | POLYGON |
| bytea | LONGBLOB |
| character [(n)] | CHAR LONGTEXT |
| character varying [(n)] | VARCHAR MEDIUMTEXT LONGTEXT |
| cidr | VARCHAR(43) |
| circle | POLYGON |
| date | DATE |
| double precision | DOUBLE |
| inet | VARCHAR(43) |
| interval [fields] [(p)] | TIME |
| JSON | LONGTEXT JSON |
| jsonb | LONGTEXT JSON |
| line | LINESTRING |
| lseg | LINESTRING |
| macaddr | VARCHAR(17) |
| money | DECIMAL(19,2) |
| numeric [(p, s)] | DECIMAL |
| path | LINESTRING |
| real | FLOAT |
| smallint | SMALLINT |
| smallserial | SMALLINT |
| serial | INT |
| text | LONGTEXT |
| time [(p)] [without time zone] | TIME |
| time [(p)] with time zone | TIME |
| timestamp [(p)] [without time zone] | DATETIME |
| timestamp [(p)] with time zone | DATETIME |
| tsquery | LONGTEXT |
| tsvector | LONGTEXT |
| uuid | VARCHAR(36) |
| xml | LONGTEXT |
| point | POINT |
| linestring | LINESTRING |
| polygon | POLYGON |
| multipoint | MULTIPOINT |
| multilinestring | MULTILINESTRING |
| multipolygon | MULTIPOLYGON |
| geometrycollection | GEOMETRYCOLLECTION |
| triangle | POLYGON |
| tin | MULTIPOLYGON |
Procedure
Create a data migration task.
Log on to the console of OMS Community Edition.
In the left-side navigation pane, click Data Migration.
On the Data Migration page, click Create Migration Task in the upper-right corner.
On the Select Source and Destination 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 target 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.Destination If you have created a data source of OceanBase Database Community Edition, 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 a data source of OceanBase Database Community Edition. Click Next.
In the dialog box that appears, click OK.
Note that this task supports only tables with a primary key or a non-null unique index. Other tables are automatically filtered out.
On the Select Migration Type page, configure the parameters.
Options for Migration Type are Schema Migration, Full Data Migration, Incremental Synchronization, Full Verification, and Reverse Increment.
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 destination database. Temporary tables are automatically filtered out. Full data migration The existing data is migrated from tables in the source database to the corresponding tables in the destination database. If you select Full Data Migration, we recommend that you use the ANALYZEstatement 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 destination database after an incremental synchronization task starts. Data changes are data addition, modification, and deletion.
Options for DML Synchronization in the Incremental Synchronization section includeInsert,Delete, andUpdate. For more information, see DML filtering.
OMS Community Edition 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 theconfirmed_flush_lsnvalue of a slot every 10 minutes. The interval can be customized. By default, archive files need to be retained for 48 hours. Therefore, OMS Community Edition 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 destination databases before full verification. For more information about how to collect statistics of OceanBase Database Community Edition, see Manually collect statistics.
- 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 data verification of only tables with a unique key.
Reverse incremental migration When a reverse incremental migration task starts, OMS Community Edition migrates the data changed in the destination database after the business switchover back to the source database in real time. You cannot select Reverse Increment in the following cases: - Data merge migration that involves multiple tables is enabled.
- Multiple source schemas map to the same destination schema.
(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 OceanBase Database Community Edition that serves as the destination, the More about Data Sources dialog box appears, prompting you to configure related parameters. For more information about the parameters, see Create a data source of OceanBase Database Community Edition.
After you configure the parameters, click Test Connectivity. After the test succeeds, click Save.
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.
- Select Specify Objects. Then select the objects to be migrated on the left and click > to add them to the list on the right. You can select tables and views of one or more databases as the migration objects.
<h4>Notice</h4>
<ul>
<li>
<p>The names of tables to be migrated, as well as the names of columns in the tables, must not contain Chinese characters. </p>
</li>
<li>
<p>If a database or table name contains double dollar signs ($$), you cannot create the migration task. </p>
</li>
</ul>
</main>
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 | <ol><li> In the list on the right of the **Specify Migration Scope** section, click **Import Objects** in the upper-right corner. <li>In the dialog box that appears, click **OK**.<br> **Notice**<br>This operation will overwrite previous selections. Proceed with caution. <li>In the **Import Objects** dialog box, import the objects to be migrated. <br>You can import CSV files to rename migration objects and set row filtering conditions. For more information, see [Download and import the settings of migration objects](../600.data-migration/1500.manage-data-migration-projects/400.download-and-import-the-settings-of-migration-objects.md). <li> Click **Validate**. <li> After the validation succeeds, click **OK**. </ol> |
| Rename objects | OMS Community Edition allows you to rename migration objects. For more information, see [Rename a database table](../600.data-migration/1600.migration-function-introduction/500.db-table-rename.md). |
| Configure settings | OMS Community Edition allows you to filter rows by using `WHERE` conditions. For more information, see [Use SQL conditions to filter data](../600.data-migration/1600.migration-function-introduction/600.migration-row-filters.md). <br>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 destination database during data mapping. <ul><li>To remove a single migration object:<br>In the list on the right of the **Specify Migration Scope** section, move the pointer over the target object, and click **Remove**. <li> To remove all migration objects:<br>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**. </ul> |
- Select Match Rules. For more information, see Configure matching rules for migration objects.
Click Next. On the Migration Options 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 Data Migration or Incremental Synchronization section. For more information about the parameters, see Coordinator.
Full data migration
The following parameters are displayed only if you have selected Full Data 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 data 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 Records Exist in Target Object Valid values: Ignore and Stop Migration. - If you select Ignore, when the data to be inserted conflicts with the existing data of a destination 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 destination contains more data than the source cannot be verified, and the verification efficiency will be decreased.
- If you select Stop Migration and a destination table contains records, an error is returned during full data migration, indicating that the migration is not allowed. In this case, you must clear the data in the destination 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.
Whether to Allow Post-indexing Specifies whether to create indexes after the full data migration is completed. Post-indexing can shorten the time required for full data 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 Data 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 destination 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;
- If you select Ignore, when the data to be inserted conflicts with the existing data of a destination table, OMS Community Edition retains the existing data and records the conflict data.
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 Data Migration, this parameter is not displayed.
- If you have selected Incremental Synchronization but not Full Data 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.
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.
Click Start Task. If you do not need to start the task now, click Save to go to the details page of the data migration 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 will be executed based on the selected migration types. For more information, see the "View migration details" section in the View details of a data migration task topic.