DeltaSourceSnapshot¶

DeltaSourceSnapshot is a SnapshotIterator and a StateCache for DeltaSource.

Creating Instance¶

DeltaSourceSnapshot takes the following to be created:

• SparkSession (Spark SQL)
• Snapshot
• Filter Expressions (Spark SQL)

DeltaSourceSnapshot is created when:

• DeltaSource is requested for the snapshot of a delta table at a given version

Initial Files (Indexed AddFiles)¶

initialFiles: Dataset[IndexedFile]

Dataset of Indexed AddFiles¶

initialFiles requests the Snapshot for all AddFiles (in the snapshot) (Dataset[AddFile]).

initialFiles sorts the AddFile dataset (Dataset[AddFile]) by modificationTime and path in ascending order.

initialFiles indexes the AddFiles (using RDD.zipWithIndex operator) that gives a RDD[(AddFile, Long)].

initialFiles converts the RDD to a DataFrame of two columns: add and index.

initialFiles adds the two new columns:

• version
• isLast as false literal

initialFiles converts (projects) DataFrame to Dataset[IndexedFile].

Creating CachedDS¶

initialFiles creates a CachedDS with the following name (with the version and path of the Snapshot):

Delta Source Snapshot #[version] - [path]

Cached Dataset of Indexed AddFiles¶

In the end, initialFiles requests the CachedDS to getDS.

Usage¶

initialFiles is used when:

• SnapshotIterator is requested for the AddFiles

Closing¶

close(
  unpersistSnapshot: Boolean): Unit

close is part of the SnapshotIterator abstraction.

close requests the Snapshot to uncache when the given unpersistSnapshot flag is enabled.