Merge pull request #2673 from paradedb/stuhood.fix-order-by-dup-string

Fix `TopDocs::order_by_string_fast_field` for duplicates

src/collector/top_score_collector.rs

@@ -1529,6 +1529,72 @@ mod tests {
         Ok(())
     }
 
+    proptest! {
+        #[test]
+        fn test_top_field_collect_string_prop(
+          order in prop_oneof!(Just(Order::Desc), Just(Order::Asc)),
+          limit in 1..256_usize,
+          offset in 0..256_usize,
+          segments_terms in
+            proptest::collection::vec(
+                proptest::collection::vec(0..32_u8, 1..32_usize),
+                0..8_usize,
+            )
+        ) {
+            let mut schema_builder = Schema::builder();
+            let city = schema_builder.add_text_field("city", TEXT | FAST);
+            let schema = schema_builder.build();
+            let index = Index::create_in_ram(schema);
+            let mut index_writer = index.writer_for_tests()?;
+
+            // A Vec<Vec<u8>>, where the outer Vec represents segments, and the inner Vec
+            // represents terms.
+            for segment_terms in segments_terms.into_iter() {
+                for term in segment_terms.into_iter() {
+                    let term = format!("{term:0>3}");
+                    index_writer.add_document(doc!(
+                        city => term,
+                    ))?;
+                }
+                index_writer.commit()?;
+            }
+
+            let searcher = index.reader()?.searcher();
+            let top_n_results = searcher.search(&AllQuery, &TopDocs::with_limit(limit)
+                .and_offset(offset)
+                .order_by_string_fast_field("city", order.clone()))?;
+            let all_results = searcher.search(&AllQuery, &DocSetCollector)?.into_iter().map(|doc_address| {
+                // Get the term for this address.
+                // NOTE: We can't determine the SegmentIds that will be generated for Segments
+                // ahead of time, so we can't pre-compute the expected `DocAddress`es.
+                let column = searcher.segment_readers()[doc_address.segment_ord as usize].fast_fields().str("city").unwrap().unwrap();
+                let term_ord = column.term_ords(doc_address.doc_id).next().unwrap();
+                let mut city = Vec::new();
+                column.dictionary().ord_to_term(term_ord, &mut city).unwrap();
+                (String::try_from(city).unwrap(), doc_address)
+            });
+
+            // Using the TopDocs collector should always be equivalent to sorting, skipping the
+            // offset, and then taking the limit.
+            let sorted_docs: Vec<_> = if order.is_desc() {
+                let mut comparable_docs: Vec<ComparableDoc<_, _, true>> =
+                    all_results.into_iter().map(|(feature, doc)| ComparableDoc { feature, doc}).collect();
+                comparable_docs.sort();
+                comparable_docs.into_iter().map(|cd| (cd.feature, cd.doc)).collect()
+            } else {
+                let mut comparable_docs: Vec<ComparableDoc<_, _, false>> =
+                    all_results.into_iter().map(|(feature, doc)| ComparableDoc { feature, doc}).collect();
+                comparable_docs.sort();
+                comparable_docs.into_iter().map(|cd| (cd.feature, cd.doc)).collect()
+            };
+            let expected_docs = sorted_docs.into_iter().skip(offset).take(limit).collect::<Vec<_>>();
+            prop_assert_eq!(
+                expected_docs,
+                top_n_results
+            );
+        }
+    }
+
     #[test]
     #[should_panic]
     fn test_field_does_not_exist() {

sstable/src/dictionary.rs

@@ -507,38 +507,58 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
     /// Returns true if and only if all terms have been found.
     pub fn sorted_ords_to_term_cb<F: FnMut(&[u8]) -> io::Result<()>>(
         &self,
-        ord: impl Iterator<Item = TermOrdinal>,
+        mut ords: impl Iterator<Item = TermOrdinal>,
         mut cb: F,
     ) -> io::Result<bool> {
+        let Some(mut ord) = ords.next() else {
+            return Ok(true);
+        };
+
+        // Open the block for the first ordinal.
         let mut bytes = Vec::new();
-        let mut current_block_addr = self.sstable_index.get_block_with_ord(0);
+        let mut current_block_addr = self.sstable_index.get_block_with_ord(ord);
         let mut current_sstable_delta_reader =
             self.sstable_delta_reader_block(current_block_addr.clone())?;
-        let mut current_ordinal = 0;
-        for ord in ord {
-            assert!(ord >= current_ordinal);
-            // check if block changed for new term_ord
-            let new_block_addr = self.sstable_index.get_block_with_ord(ord);
-            if new_block_addr != current_block_addr {
-                current_block_addr = new_block_addr;
-                current_ordinal = current_block_addr.first_ordinal;
-                current_sstable_delta_reader =
-                    self.sstable_delta_reader_block(current_block_addr.clone())?;
-                bytes.clear();
-            }
+        let mut current_block_ordinal = current_block_addr.first_ordinal;
 
-            // move to ord inside that block
-            for _ in current_ordinal..=ord {
+        loop {
+            // move to the ord inside the current block
+            while current_block_ordinal <= ord {
                 if !current_sstable_delta_reader.advance()? {
                     return Ok(false);
                 }
                 bytes.truncate(current_sstable_delta_reader.common_prefix_len());
                 bytes.extend_from_slice(current_sstable_delta_reader.suffix());
+                current_block_ordinal += 1;
             }
-            current_ordinal = ord + 1;
             cb(&bytes)?;
+
+            // fetch the next ordinal
+            let Some(next_ord) = ords.next() else {
+                return Ok(true);
+            };
+
+            // advance forward if the new ord is different than the one we just processed
+            //
+            // this allows the input TermOrdinal iterator to contain duplicates, so long as it's
+            // still sorted
+            if next_ord < ord {
+                panic!("Ordinals were not sorted: received {next_ord} after {ord}");
+            } else if next_ord > ord {
+                // check if block changed for new term_ord
+                let new_block_addr = self.sstable_index.get_block_with_ord(next_ord);
+                if new_block_addr != current_block_addr {
+                    current_block_addr = new_block_addr;
+                    current_block_ordinal = current_block_addr.first_ordinal;
+                    current_sstable_delta_reader =
+                        self.sstable_delta_reader_block(current_block_addr.clone())?;
+                    bytes.clear();
+                }
+                ord = next_ord;
+            } else {
+                // The next ord is equal to the previous ord: no need to seek or advance.
+            }
         }
-        Ok(true)
     }
 
     /// Returns the number of terms in the dictionary.