At least C++ (and the IPC format) a schema can be shared across the many RecordBatch's which might have different sources.
It might be useful to define a reserved metadata key (similar to extension types) so that the data can be interpreted consistently. On Wed, Feb 24, 2021 at 11:29 AM Andrew Lamb <al...@influxdata.com> wrote: > I wonder if you could add the file_name as metadata on the `Schema` of the > RecordBatch rather than the RecordBatch itself? Since every RecordBatch has > a schema, I don't fully understand the need to add something additional to > the RecordBatch > > > https://docs.rs/arrow/3.0.0/arrow/datatypes/struct.Schema.html#method.new_with_metadata > > On Wed, Feb 24, 2021 at 1:20 AM Mike Seddon <seddo...@gmail.com> wrote: > > > Hi, > > > > One of Apache Spark's very useful SQL functions is the 'input_file_name' > > SQL function which provides a simple API for identifying the source of a > > row of data when sourced from a file-based source like Parquet or CSV. > This > > is particularly useful for identifying which chunk/partition of a Parquet > > the row came from and is used heavily by the DeltaLake format to > determine > > which files are impacted for MERGE operations. > > > > I have built a functional proof-of-concept for DataFusion but it requires > > modifying the RecordBatch struct to include a 'metadata' struct > > (RecordBatchMetadata) to carry the source file name attached to each > batch. > > > > It also requires changing the ScalarFunctionImplementation signature to > > support exposing the metadata (and therefore all the functions). > > > > From: <Arc<dyn Fn(&[ColumnarValue]) -> Result<ColumnarValue> + Send + > > Sync>; > > To: <Arc<dyn Fn(&[ColumnarValue], RecordBatchMetadata) -> > > Result<ColumnarValue> + Send + Sync>; > > > > These changes have been made in a personal feature branch and are > available > > for review (still needs cleaning) but conceptually does anyone have a > > problem with this API change or have a better proposal? > > > > Thanks > > Mike > > >
