phillipleblanc opened a new issue, #15173:
URL: https://github.com/apache/datafusion/issues/15173
### Is your feature request related to a problem or challenge?
The `ListingTableProvider` in DataFusion provides an implementation of a
`TableProvider` that organizes a collection of (potentially hive partitioned)
files in an object store into a single table.
Similar to how hive partitions are injected into the listing table schema,
but they don't actually exist in the physical parquet files - I'd like to be
able to request the ListingTable to inject metadata columns that get their data
from the `ObjectMeta` provided by the object store crate. Then I can query for
and filter on the columns `location`, `size` and `last_modified`).
I'd also like queries that filter on the metadata columns to be able to
prune out files, similar to partition pruning. I.e. if I do `SELECT * FROM
my_listing_table WHERE last_modified > '2025-03-10'` then only files that were
modified after `'2025-03-10'` should be passed to the FileScanConfig to be read.
My scenario is I'd like to be able to efficiently ingest files from an
object store bucket that I haven't seen before - and filtering on
`last_modified` seems like a good solution.
This could potentially fold into the work ongoing in #13975 / #14057 /
#14362 to mark these columns as proper system/metadata columns - but it
fundamentally isn't blocked on that work. Since this would be an opt-in from
the consumer, automatic filtering out on a `SELECT *` doesn't seem required.
### Describe the solution you'd like
A new API on the `ListingOptions` struct that is passed to a
`ListingTableConfig` which is passed to `ListingTable::try_new`.
```rust
/// Set metadata columns on [`ListingOptions`] and returns self.
///
/// "metadata columns" are columns that are computed from the
`ObjectMeta` of the files from object store.
///
/// Available metadata columns:
/// - `location`: The full path to the object
/// - `last_modified`: The last modified time
/// - `size`: The size in bytes of the object
///
/// For example, given the following files in object store:
///
/// ```text
/// /mnt/nyctaxi/tripdata01.parquet
/// /mnt/nyctaxi/tripdata02.parquet
/// /mnt/nyctaxi/tripdata03.parquet
/// ```
///
/// If the `last_modified` field in the `ObjectMeta` for
`tripdata01.parquet` is `2024-01-01 12:00:00`,
/// then the table schema will include a column named `last_modified`
with the value `2024-01-01 12:00:00`
/// for all rows read from `tripdata01.parquet`.
///
/// | <other columns> | last_modified |
/// |-----------------|-----------------------|
/// | ... | 2024-01-01 12:00:00 |
/// | ... | 2024-01-02 15:30:00 |
/// | ... | 2024-01-03 09:15:00 |
///
/// # Example
/// ```
/// # use std::sync::Arc;
/// # use datafusion::datasource::{listing::ListingOptions,
file_format::parquet::ParquetFormat};
///
/// let listing_options = ListingOptions::new(Arc::new(
/// ParquetFormat::default()
/// ))
/// .with_metadata_cols(vec![MetadataColumn::LastModified]);
///
/// assert_eq!(listing_options.metadata_cols,
vec![MetadataColumn::LastModified]);
/// ```
pub fn with_metadata_cols(mut self, metadata_cols: Vec<MetadataColumn>)
-> Self {
self.metadata_cols = metadata_cols;
self
}
```
The definition for `MetadataColumn` is a simple enum:
```rust
/// A metadata column that can be used to filter files
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum MetadataColumn {
/// The location of the file in object store
Location,
/// The last modified timestamp of the file
LastModified,
/// The size of the file in bytes
Size,
}
```
The order of the `MetadataColumn` passed into `with_metadata_cols` denotes
the order it will appear in the table schema. Metadata columns will be added
after partition columns.
### Describe alternatives you've considered
I considered what it might look like to make `ListingTableProvider` more
extensible to be able to implement these changes without a core DataFusion
change. I wasn't able to come up with anything simpler than the above though.
Another option might be to make a lot of the internals of
ListingTableProvider public so that it is easier for people to maintain their
own customized versions of ListingTableProvider.
### Additional context
I've already implemented this in my project, I will be upstreaming my change
and linking to this issue. To view what this looks like already implemented,
see: https://github.com/spiceai/datafusion/pull/74
And to see the changes needed to integrate with it from a consuming project,
see: https://github.com/spiceai/spiceai/pull/4970 (It is quite contained, which
I'm happy with)
This change will have no visible effect on consumers - they need to
explicitly opt-in to see the metadata columns.
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