Incremental Migration of Relational Databases

CDM supports incremental migration of relational databases. After a full migration is complete, data in a specified period can be incrementally migrated. For example, data added on the previous day can be exported at 00:00:00 every day.

Migrating incremental data within a specified period of time
- Application scenarios: The source end is a relational database. The destination end can be of any type.
- Key configurations: WHERE Clause and Schedule Execution
- Prerequisites: The data table contains a date and time field or timestamp field.

In incremental migration, only the specified data is written to the data table. The existing records are not updated or deleted.

If you have configured a macro variable of date and time and schedule a CDM job through DataArts Studio DataArts Factory, the system replaces the macro variable of date and time with (Planned start time of the data development job – Offset) rather than (Actual start time of the CDM job – Offset).

WHERE Clause

Parameter position: When creating a table/file migration job, if the source end is a relational database, the Where Clause parameter is available in the advanced attributes of Source Job Configuration.
Parameter principle: Set WHERE Clause to an SQL statement, for example, age > 18 and age <= 60, CDM exports only the data that meets the SQL statement requirement. If WHERE Clause is not specified, the entire table is exported.
Where Clause can be set to macro variables of date and time. When the data table contains the date or timestamp field, Where Clause and Schedule Execution can be used together to extract data of a specified date.
Example configurations:
Suppose that the database table contains column DS indicating the time, the value type of the column is varchar(30), and the inserted time format is similar to 2017-xx-xx. See Figure 1. Set the parameters as follows:

Figure 1 Table data
1. WHERE Clause: Set this parameter to DS='${dateformat(yyyy-MM-dd,-1,DAY)}'.
  Figure 2 WHERE Clause
2. Scheduling job execution: Set Cycle (days) to 1 and Start Time to 00:00:00.
In this way, all data generated on the previous day can be exported at 00:00:00 every day. WHERE Clause can be configured to various macro variables of date and time. You can use the macro variables of date and time and scheduled jobs with specified cycle of minutes, hours, days, weeks, or months together to automatically export data at a specific time.