# Log-based and trigger-based capture modes The log-based mode and the trigger-based mode are two different modes of capture. | Capture mode | Description | | --- | --- | | Log-based | The journal (.JRN file) is created at the
installation step (during the [journalization](https://help.qlik.com/talend/r/en-US/7.3/change-data-capture-user-guide/journalizing-database)
process), in the selected directory.

The capture engine stores the transactions in the .JRN file and
those transactions are then read by the source engine.

Information noteNote: With an AS/400 IBMi source database, there is no
.JRN file. The capture engine
directly reads the database. | | Trigger-based | A dd\_journal table of transaction logs
is created in each source database.

![](https://help.qlik.com/talend/en-US/change-data-capture-installation-guide/Resources/images/tcdc-trigger-ddjournal-table.png)

The capture engine reads transactions from this
intermediate table. They are then stored in the
.JRN file and deleted from the
intermediate table. Eventually, the source engine reads those
transactions.

Information noteNote: The source database may be triggered by other programs
than Talend Change Data Capture (for example, an ERP), and only one trigger can be
performed on a table. These limitations can raise
performance issues and have an impact on the user
profiles.


Trigger functions are created by Talend Change Data Captureand can be viewed in their database client management software,
next to the table or next to the database.

In case of structural
changes of the database (e.g. a column addition), it is possible
to rebuild the trigger manually, so that the database trigger
functions can take these changes into account.

To do so:
from Journal Management window,
right-click the table to access rebuild the
trigger. ![](https://help.qlik.com/talend/en-US/change-data-capture-installation-guide/Resources/images/tcdc-rebuild-trigger.png) | ## Support according to the source database Some source databases support only one of the two modes: * log-based mode only: AS/400 IBMi and Oracle between v10 and v19c (through the LogMiner), * trigger-based mode only: PostgreSQL≥9.2, MySQL, MariaDB and Oracle between v8 and v10. For all other source databases, both modes are supported. Information noteNote: Oracle≥v10 support log-based as well as trigger-based modes. Follow the requirements detailed for each source database, as they are different according to the capture mode.