Home | Table of Contents | Check Interval, Task and Use Cases | CloverETL 4.6.1
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### Check Interval, Task and Use Cases

- User may specify the minimum time interval between two checks. The interval is specified in seconds. Check every

- Each listener defines a task, which will be processed as a reaction for the file event. All task types and theirs attributes are described in Scheduling and GraphEventListeners sections.

  - Graph Execution, when a file with input data is accessible

  - Graph Execution, when a file with input data is updated

  - Graph Execution, when a file with generated data is removed and must be recreated

#### How to use source of event during task processing

A file(s), which caused event (considered as source of the event) may be used during task processing. CloverETL graph/jobflow components with "File URL" attribute (e.g. reader or writer components) may directly use event source by parameter placeholder: `${EVENT_FILE_URLS}`. Please see Executed by Task "graph execution" by File Event Listener to see another parameters.

Please note that previous versions used lower-case placeholders. Since version 3.3, placeholders are upper-case, however lower-case still work for backward compatibility.

For "graph execution" task this works only if the graph is not pooled. Thus "keep in pool interval" must be set to 0 (default value).

#### Delayed triggering for incomplete files

It is possible to delay task execution for incomplete files. This is useful in cases, when the condition to execute the listener's task has been met, but there is still some work that needs to be done on the file, e.g. the whole file needs to be uploaded.

##### Ignore empty files

If the process creating the file creates an empty file and does something else for several minutes or even hours, and finally writes the content, tick Ignore empty files checkbox. The task will be triggered only if a non-empty file appears.

##### Trigger task when file has not changed for n checks

If the file size slowly rises till the file is complete, tick the checkbox Trigger task when file has not changed. Then specify the number of additional file size checks that are to be performed on the file. The listener's task will not be triggered until the checks are performed and the file's size stays the same between these checks.

##### Combination

If you use Ignore empty files and Trigger task when file has not changed for n checks together, the first one filters out empty files and the later one the files that are being changed. The task will be triggered only on files that are not empty and that have not changed for the specified number of checks.

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