Skip to main content

Error Handling at Source

Errors from stream elements that subscribe to a source are propagated to the source that emitted the event. This behavior can now be modified by implementing the OnError.action property within the stream definition.

The following actions are supported for error handling at source:

  • log - Logs the error, and drops the message.
  • stream - Forward the error and the event to fault stream. This stream, indicated as !<StreamName>, is created implicitly and captures both the event that led to the error and the error details. A fault stream will be composed of the base stream’s attributes, plus an _error attribute containing error details.

OnError.action Property​

Apply the OnError.action property to a source to handle errors.

CREATE SOURCE <stream name> WITH (type='<source type>', OnError.action='<action>', <other properties>) (<attribute name> <attribute type>, ...);

Fault Stream Details​

The fault stream automatically captures errors from the associated base stream. The system generates this stream without explicit user definition.

Example: Source with Fault Stream​

-- Stream definition with OnError.action='stream' to capture errors
CREATE SOURCE CountStream WITH (type='inMemory', map.type='passthrough', OnError.action='stream') (c long, t long);

-- Automatically created fault stream schema
CREATE STREAM !CountStream (c long, t long, _error object);

-- Insert logic for the main stream
INSERT INTO CountStream
SELECT count() as c, eventTimestamp() as t
FROM EventTrigger;

-- Error handling by redirection to the fault stream
INSERT INTO CountStreamErrorStream
SELECT c, t, convert(_error, 'string') as error
FROM !CountStream;

The provided example illustrates the application of OnError.action='stream' to a stream source, which directs error handling to a fault stream.