diff --git a/rust/lance-table/benches/row_id_index.rs b/rust/lance-table/benches/row_id_index.rs
index a951622005c..dd20fccb639 100644
--- a/rust/lance-table/benches/row_id_index.rs
+++ b/rust/lance-table/benches/row_id_index.rs
@@ -27,7 +27,7 @@ use lance_core::utils::deletion::DeletionVector;
 use lance_io::ReadBatchParams;
 use lance_select::{RowAddrMask, RowAddrTreeMap};
 use lance_table::format::pb;
-use lance_table::rowids::FragmentRowIdIndex;
+use lance_table::rowids::{FragmentRowIdIndex, segment::U64Segment};
 use lance_table::{
     rowids::{RowIdIndex, RowIdSequence, read_row_ids, write_row_ids},
     utils::stream::{RowIdAndDeletesConfig, apply_row_id_and_deletes},
@@ -70,6 +70,36 @@ fn make_frag_sequences(
         .collect()
 }
 
+fn make_clustered_range_frag_sequences(num_rows: u64) -> Vec<FragmentRowIdIndex> {
+    let rows_per_fragment = num_rows / 100;
+    (0_u32..100)
+        .map(|fragment_id| {
+            let start = fragment_id as u64 * rows_per_fragment;
+            let end = start + rows_per_fragment;
+            let mut ranges = Vec::new();
+            let mut row_id = start;
+            while row_id < end {
+                let present_end = (row_id + 250).min(end);
+                ranges.push(row_id..present_end);
+                row_id = present_end.saturating_add(250);
+            }
+            let wire_sequence = pb::RowIdSequence {
+                segments: ranges
+                    .into_iter()
+                    .map(|range| pb::U64Segment::from(U64Segment::Range(range)))
+                    .collect(),
+            };
+            // Decode the wire ranges into the compact form used after PR #9311.
+            let sequence = read_row_ids(&wire_sequence.encode_to_vec()).unwrap();
+            FragmentRowIdIndex {
+                fragment_id,
+                row_id_sequence: Arc::new(sequence),
+                deletion_vector: Arc::new(DeletionVector::default()),
+            }
+        })
+        .collect()
+}
+
 // For range of values
 // https://bheisler.github.io/criterion.rs/book/user_guide/benchmarking_with_inputs.html
 
@@ -199,6 +229,11 @@ fn bench_creation(c: &mut Criterion) {
         );
     }
 
+    let clustered_indices = make_clustered_range_frag_sequences(num_rows());
+    group.bench_function("BuildIndexClusteredRanges", |b| {
+        b.iter(|| std::hint::black_box(RowIdIndex::new(&clustered_indices).unwrap()));
+    });
+
     group.finish();
 }
 
diff --git a/rust/lance-table/src/rowids/index.rs b/rust/lance-table/src/rowids/index.rs
index c4d7b8f3771..b04ff744eab 100644
--- a/rust/lance-table/src/rowids/index.rs
+++ b/rust/lance-table/src/rowids/index.rs
@@ -557,6 +557,15 @@ fn decompose_segment_no_deletions(segment: &U64Segment, start_address: u64) -> O
             let coverage = range.start..=range.end - 1;
             Some((coverage, (row_id_segment, address_segment)))
         }
+        U64Segment::Ranges { .. } if !segment.is_empty() => {
+            // Without deletions, a live ID's position is also its physical
+            // offset within this segment.
+            let row_id_segment = segment.clone();
+            let address_segment =
+                U64Segment::Range(start_address..start_address + row_id_segment.len() as u64);
+            let coverage = row_id_segment.range()?;
+            Some((coverage, (row_id_segment, address_segment)))
+        }
         _ if segment.is_empty() => None,
         _ => {
             // Non-Range segments: must iterate to build address mapping.
@@ -801,6 +810,100 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_merged_index_keeps_ranges_segments_compact() {
+        let row_id_ranges = [100..103, 108..110, 115..119];
+        let sequence = RowIdSequence(vec![
+            U64Segment::Range(50..53),
+            U64Segment::from_sorted_ranges(&row_id_ranges).unwrap(),
+        ]);
+        let source = fragment(7, sequence);
+        let index = RowIdIndex::new(std::slice::from_ref(&source)).unwrap();
+
+        let merged = index.merged.as_ref().expect("small input should be merged");
+        assert!(matches!(
+            merged.get(&100).unwrap().0,
+            U64Segment::Ranges { .. }
+        ));
+
+        for (row_id, row_offset) in [
+            (50, 0),
+            (51, 1),
+            (52, 2),
+            (100, 3),
+            (101, 4),
+            (102, 5),
+            (108, 6),
+            (109, 7),
+            (115, 8),
+            (116, 9),
+            (117, 10),
+            (118, 11),
+        ] {
+            assert_eq!(
+                index.get(row_id).unwrap(),
+                Some(RowAddress::new_from_parts(7, row_offset)),
+                "row id {row_id}"
+            );
+        }
+        for missing in [49, 53, 99, 103, 107, 110, 114, 119, 120] {
+            assert_eq!(index.get(missing).unwrap(), None, "row id {missing}");
+        }
+        assert_eq!(
+            index.get_many(&[108, 53, 100, 108]).unwrap(),
+            vec![
+                Some(RowAddress::new_from_parts(7, 6)),
+                None,
+                Some(RowAddress::new_from_parts(7, 3)),
+                Some(RowAddress::new_from_parts(7, 6)),
+            ]
+        );
+    }
+
+    #[test]
+    fn test_overlapping_ranges_chunks_keep_row_addresses() {
+        let left_ranges = [100..103, 108..110, 115..119];
+        let right_ranges = [103..108, 110..115];
+        let sources = [
+            fragment(
+                7,
+                RowIdSequence(vec![U64Segment::from_sorted_ranges(&left_ranges).unwrap()]),
+            ),
+            fragment(
+                8,
+                RowIdSequence(vec![U64Segment::from_sorted_ranges(&right_ranges).unwrap()]),
+            ),
+        ];
+        let index = RowIdIndex::new(&sources).unwrap();
+
+        for row_id in 100..119 {
+            let (fragment_id, row_offset) = if (100..103).contains(&row_id)
+                || (108..110).contains(&row_id)
+                || (115..119).contains(&row_id)
+            {
+                let row_offset = match row_id {
+                    100..=102 => row_id - 100,
+                    108..=109 => row_id - 105,
+                    115..=118 => row_id - 110,
+                    _ => unreachable!(),
+                };
+                (7, row_offset)
+            } else {
+                let row_offset = match row_id {
+                    103..=107 => row_id - 103,
+                    110..=114 => row_id - 105,
+                    _ => unreachable!(),
+                };
+                (8, row_offset)
+            };
+            assert_eq!(
+                index.get(row_id).unwrap(),
+                Some(RowAddress::new_from_parts(fragment_id, row_offset as u32)),
+                "row id {row_id}"
+            );
+        }
+    }
+
     #[test]
     fn test_deep_overlap_merges_however_many_rows_it_reads() {
         // Just past the row budget in total, interleaved so every fragment