peter-toth opened a new issue, #3596:
URL: https://github.com/apache/parquet-java/issues/3596
### Describe the enhancement requested
`org.apache.parquet.internal.filter2.columnindex.RowRanges` is currently only
constructible internally — instances are produced by column-index filtering
(`ColumnIndexFilter.calculateRowRanges(...)`) or by the package-private
factory/union helpers. All of its constructors are `private`, so there is no
supported way for code outside the package to build a `RowRanges` from an
arbitrary set of selected rows.
This is limiting for external readers that determine which rows to read from
some other source than column-index filtering. A concrete motivating case is
a
materialization path that receives a stream of selected row indices from a
downstream operator (for example, the row positions surviving a filter or
join)
and needs to turn that stream into a `RowRanges` to drive reads — without
knowing page boundaries ahead of time.
#### Proposed change
Add a small `RowRanges.Builder` that lets callers append selected row indices
incrementally and coalesces consecutive indices into `Range` entries:
```java
RowRanges.Builder builder = RowRanges.builder();
for (long row : selectedRowsInOrder) {
builder.addSelected(row);
}
RowRanges ranges = builder.build();
```
Semantics:
- `addSelected(long)` must be called in **strictly increasing** order.
Consecutive indices are merged into a single `Range`; a gap closes the
current
run and starts a new one.
- Calling `addSelected` with a value `<=` the previous value throws
`IllegalArgumentException` (rejects out-of-order and duplicate indices).
- `build()` returns `RowRanges.EMPTY` when no rows were selected.
#### Why a builder (vs. exposing a constructor)
A builder keeps `RowRanges` immutable and its internal `Range` list
encapsulated, while still letting callers feed rows one at a time. The
coalescing logic lives in one place rather than being re-implemented by each
external caller, and the strictly-increasing contract is enforced at the
point
of construction.
#### Scope
- Additive, `Core` only. No change to existing `RowRanges` behavior or to the
column-index filtering path.
- No user-facing API removal or behavioral change to existing methods.
This is the first of two related enhancements opening up
`RowRanges`/reader APIs needed by the materialization feature described
above; a
follow-up will expose per-row-range reader APIs on `ParquetFileReader`.
> Component(s): **Core**
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