Source Contract — Streaming Sources for Micro-Batch Stream Processing (Data Source API V1)

Source is the extension of the BaseStreamingSource contract for streaming sources that work with "continuous" stream of data identified by offsets.

Source is part of Data Source API V1 and used in Micro-Batch Stream Processing only.

For fault tolerance, Source must be able to replay an arbitrary sequence of past data in a stream using a range of offsets. This is the assumption so Structured Streaming can achieve end-to-end exactly-once guarantees.

Method Description

commit

commit(end: Offset): Unit

Commits data up to the end offset, i.e. informs the source that Spark has completed processing all data for offsets less than or equal to the end offset and will only request offsets greater than the end offset in the future.

Used exclusively when MicroBatchExecution stream execution engine (Micro-Batch Stream Processing) is requested to write offsets to a commit log (walCommit phase) while running an activated streaming query.

getBatch

getBatch(
  start: Option[Offset],
  end: Offset): DataFrame

Generating a streaming DataFrame with data between the start and end offsets

Start offset can be undefined (None) to indicate that the batch should begin with the first record

Used when MicroBatchExecution stream execution engine (Micro-Batch Stream Processing) is requested to run an activated streaming query, namely:

getOffset

getOffset: Option[Offset]

Latest (maximum) offset of the source (or None to denote no data)

Used exclusively when MicroBatchExecution stream execution engine (Micro-Batch Stream Processing) is requested for latest offsets of all sources (getOffset phase) while running activated streaming query.

schema

schema: StructType

Schema of the source

Note	`schema` seems to be used for tests only and a duplication of StreamSourceProvider.sourceSchema.

Table 2. Sources
Source	Description
FileStreamSource	Part of file-based data sources (`FileFormat`)
KafkaSource	Part of kafka data source

Source

Source Contract — Streaming Sources for Micro-Batch Stream Processing (Data Source API V1)

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