PostgreSQL

This section explains how to create data migration tasks through the Explorer interface to migrate data from PostgreSQL to the current TDengine cluster.

Function Overview

PostgreSQL is a powerful open-source client/server relational database management system that has many features found in large commercial RDBMSs, including transactions, subqueries, triggers, views, foreign key referential integrity, and complex locking capabilities.

TDengine can efficiently read data from PostgreSQL and write it to TDengine for historical data migration or real-time data synchronization.

Creating a Task

1. Add a Data Source

Click the +Add Data Source button in the upper left corner of the data writing page to enter the Add Data Source page, as shown below:

2. Configure Basic Information

In the Name field, enter a task name, such as test_postgres_01.

Select PostgreSQL from the Type dropdown list, as shown below (the fields on the page will change after selection).

The Agent field is optional; if needed, you can select a specified agent from the dropdown or click the +Create New Agent button on the right to create a new agent.

The Target Database field is required; you can first click the +Create Database button on the right to create a new database.

3. Configure Connection Information

In the Connection Configuration area, fill in the source PostgreSQL database connection information, as shown below:

4. Configure Authentication Information

In the User field, enter the user for the source PostgreSQL database; this user must have read permissions in the organization.

In the Password field, enter the login password for the user in the source PostgreSQL database.

5. Configure Connection Options

In the Application Name field, set the application name to identify the connecting application.

In the SSL Mode field, set whether to negotiate a secure SSL TCP/IP connection with the server or prioritize how to negotiate it. The default value is PREFER. Optional values include DISABLE, ALLOW, PREFER, and REQUIRE.

Then click the Check Connectivity button; users can click this button to check if the information filled in above can successfully retrieve data from the source PostgreSQL database.

6. Configure SQL Query

The Subtable Fields are used to split the subtable fields. It is a select distinct SQL statement that queries unique combinations of specified fields, typically corresponding to tags in the transform section:

This configuration is primarily aimed at solving the problem of data migration disorder and needs to be used in conjunction with the SQL Template; otherwise, the expected effect cannot be achieved. Here are usage examples:

1. Fill in the subtable fields with the statement select distinct col_name1, col_name2 from table, indicating that the fields col_name1 and col_name2 from the source table will be used to split the subtables of the target supertable.
2. In the SQL Template, add placeholders for the subtable fields, such as ${col_name1} and ${col_name2} in select * from table where ts >= ${start} and ts < ${end} and ${col_name1} and ${col_name2}.
3. In the transform section, configure the tag mappings for col_name1 and col_name2.

The SQL Template is an SQL statement template used for querying. The SQL statement must include time range conditions, and the start and end times must appear in pairs. The time range defined in the SQL statement template consists of a column representing time from the source database and the placeholders defined below.

SQL uses different placeholders to represent different time format requirements, specifically the following placeholder formats:

1. ${start} and ${end}: Represent RFC3339 formatted timestamps, e.g., 2024-03-14T08:00:00+0800
2. ${start_no_tz} and ${end_no_tz}: Represent RFC3339 strings without timezone: 2024-03-14T08:00:00
3. ${start_date} and ${end_date}: Represent only the date, e.g., 2024-03-14

To solve the problem of migration data disorder, sorting conditions should be added to the query statement, such as order by ts asc.

Start Time is the starting time for migrating data; this is a required field.

End Time is the end time for migrating data and can be left blank. If set, the migration task will complete automatically when it reaches the end time; if left blank, it will continuously synchronize real-time data, and the task will not automatically stop.

Query Interval is the time interval for segmenting queries. The default is 1 day. To avoid querying an excessive amount of data, a sub-task for data synchronization will query data by time segments according to the query interval.

Delay Duration is an integer range from 1 to 30; to avoid the loss of delayed written data in real-time synchronization scenarios, each synchronization task will read data before the specified delay duration.

7. Configure Data Mapping

In the Data Mapping area, fill in the parameters related to data mapping.

Click the Retrieve from Server button to get sample data from the PostgreSQL server.

In the Extract or Split from Columns section, fill in the fields to extract or split from the message body. For example, split the vValue field into vValue_0 and vValue_1 using the split extractor, specifying , as the separator and 2 for the number.

In the Filtering section, enter filtering conditions; for example, entering Value > 0 means that only data where Value is greater than 0 will be written to TDengine.

In the Mapping section, select the supertable to map to TDengine and specify the columns to map to the supertable.

Click Preview to view the mapping results.

8. Configure Advanced Options

The Advanced Options area is folded by default; click the > button on the right to expand, as shown below:

Maximum Read Concurrency limits the number of connections to the data source or the number of reading threads. Modify this parameter when the default parameters do not meet your needs or when you need to adjust resource usage.

Batch Size is the maximum number of messages or rows sent at one time. The default is 10,000.

9. Completion

Click the Submit button to complete the creation of the data synchronization task from PostgreSQL to TDengine. Return to the Data Source List page to view the task execution status.