To access feature type format parameters, open the Feature Type Properties dialog by clicking the properties 
button on a feature type in the workspace.
These parameters apply only to a selected feature type, not to the entire writer.
Tip: If a feature type parameter listed here conflicts with a writer-level parameter, then the writer parameter will be ignored and this feature type parameter will be used.
Layer Settings
Writer Mode
This parameter sets the default writer mode for the feature type, which can be overridden by the fme_db_operation attribute on features.
See Writer Mode Selection for details.
Truncate First
If Yes, the writer deletes all features from the layer upon receiving the first feature for the corresponding feature type.
The ArcGIS Online Feature Service writer performs a truncation by reading all feature IDs from the layer, and then making deletion requests in batches according to the Features Per Request advanced parameter.