docs: document >2GB file advantage over Parquet; add TODO for large-file test

Vortex uses uint64 offsets in the footer and uint32 segment lengths,
avoiding Parquet's 2GB column-chunk limit (int32 page-size field).
The FFM MemorySegment API maps files of arbitrary size, unlike the
legacy FileChannel.map() which caps each mapping at 2GB.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: dfa1

README.md

@@ -18,6 +18,17 @@ reads, making it easier to:
 - build and test on any platform with a standard JDK
 - debug and profile with standard JVM tooling
 
+## Why Vortex instead of Parquet
+
+| | Parquet | Vortex |
+|---|---------|--------|
+| Max column-chunk size | 2 GB (`int32` page offsets) | 4 GB per segment (`uint32` length) |
+| Max file offset | 2 GB (`int32` on some implementations) | 16 EB (`uint64` in footer) |
+| Encoding extensibility | Fixed codec set | Plugin registry, any encoding |
+
+Files larger than 2 GB are a practical problem with Parquet: the `int32` data-page size field in the page header caps individual column chunks at 2 GB.
+Vortex uses `uint64` offsets throughout the footer, and this library maps files with `MemorySegment` (Java FFM API), which has no per-mapping size limit — unlike the legacy `FileChannel.map()` API that caps each mapping at 2 GB.
+
 ## Prior art and inspiration
 
 | Project | Language | Notes |

TODO.md

@@ -123,4 +123,12 @@
 - move the project in a dedicated organization
 - create website
 - publish benchmarks
-- idea is to build something like hardwood.dev but for parquet files
+- idea is to build something like hardwood.dev but for parquet files
+
+## Large-file support
+
+- [ ] **#12 Test read/write of files > 2 GB**
+  - Write a vortex file whose total segment data exceeds 2 GB (e.g., several wide int64 columns × enough rows)
+  - Verify `VortexFile.open()` maps correctly and `ScanIterator` decodes without offset truncation
+  - Parquet baseline for comparison: same data fails or requires splitting when any column chunk > 2 GB
+  - Confirm no `int` casts silently truncate `uint64` offsets or `uint32` lengths in `SegmentSpec`