Repeatable streams and DataWeave streaming
How Mule 4 repeatable and non-repeatable streams behave, how to size file-store and in-memory buffers, how auto-paged objects are buffered by instance count, why streams should be consumed promptly, and how to make DataWeave read and write large documents as streams.
Design Mule applications using available streaming features in Mule.
~7 min read · 6 practice questions
What the exam expects
- Choose between repeatable file-store, repeatable in-memory and non-repeatable streams from how a flow reads the payload and which Mule edition runs it.
- Size a stream buffer for the payload and concurrency, and know which components silently consume a whole stream.
- Estimate memory for auto-paged connector output, whose buffer counts objects rather than bytes.
- Enable DataWeave streaming on input and output, and judge whether a script can run in streaming mode.
Repeatable stream: a stream Mule buffers so it can be read more than once and concurrently. Non-repeatable stream: a stream that can be read only once, with repeatable buffering disabled. inMemorySize: the file-store buffer size held in memory before Mule writes to disk. Streaming reader property: streaming=true on a source's MIME type, which makes DataWeave read the data as a stream. Deferred mode: deferred=true on a DataWeave output directive, which passes the output stream directly to the next processor (Streaming in Mule Apps, Streaming in DataWeave).
Key facts
- Detail
- Repeatable streams
- Detail
- Mule EE default and EE only; 512 KB in memory, then a temporary file
- Detail
- Mule Kernel default; 512 KB, grows by 512 KB; fails past the maximum
- Detail
- Fewer disk writes, fewer concurrent requests
- Detail
- Proportional to stream size
- Detail
- Instance count
- Detail
- 500 objects in memory, rest serialized to disk
- Detail
- Off; needs
streaming=trueon the source MIME type
- Detail
- Needs both
collectionPathandstreaming=true
deferred=true- Detail
- Output goes straight to the next processor; exceptions are not handled
- When does the
@StreamCapable()validator accept a script? - Why can
@StreamCapable()reject a JSON script that streams correctly in your tests? - Which connectors does the streaming page list among the components that support repeatable streams?
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