Fix outdated variable naming and comments to alive bitset (#1387)

* Fix outdated variables and comments for alive bitset

* Fix expired link to delete bitset

ARCHITECTURE.md

@@ -57,8 +57,8 @@ For a better idea of how indexing works, you may read the [following blog post](
 
 Deletes happen by deleting a "term". Tantivy does not offer any notion of primary id, so it is up to the user to use a field in their schema as if it was a primary id, and delete the associated term if they want to delete only one specific document.
 
-On commit, tantivy will find all of the segments with documents matching this existing term and create a [tombstone file](src/fastfield/delete.rs) that represents the bitset of the document that are deleted.
-Like all segment files, this file is immutable. Because it is possible to have more than one tombstone file at a given instant, the tombstone filename has the format ``` segment_id . commit_opstamp . del```.
+On commit, tantivy will find all of the segments with documents matching this existing term and remove from [alive bitset file](src/fastfield/alive_bitset.rs) that represents the bitset of the alive document ids.
+Like all segment files, this file is immutable. Because it is possible to have more than one alive bitset file at a given instant, the alive bitset filename has the format ``` segment_id . commit_opstamp . del```.
 
 An opstamp is simply an incremental id that identifies any operation applied to the index. For instance, performing a commit or adding a document.
 

src/core/segment_component.rs

@@ -24,7 +24,8 @@ pub enum SegmentComponent {
     Store,
     /// Temporary storage of the documents, before streamed to `Store`.
     TempStore,
-    /// Bitset describing which document of the segment is deleted.
+    /// Bitset describing which document of the segment is alive.
+    /// (It was representing deleted docs but changed to represent alive docs from v0.17)
     Delete,
 }
 

src/core/segment_reader.rs

@@ -175,9 +175,9 @@ impl SegmentReader {
         let fieldnorm_readers = FieldNormReaders::open(fieldnorm_data)?;
 
         let original_bitset = if segment.meta().has_deletes() {
-            let delete_file_slice = segment.open_read(SegmentComponent::Delete)?;
-            let delete_data = delete_file_slice.read_bytes()?;
-            Some(AliveBitSet::open(delete_data))
+            let alive_doc_file_slice = segment.open_read(SegmentComponent::Delete)?;
+            let alive_doc_data = alive_doc_file_slice.read_bytes()?;
+            Some(AliveBitSet::open(alive_doc_data))
         } else {
             None
         };
@@ -295,8 +295,7 @@ impl SegmentReader {
         self.delete_opstamp
     }
 
-    /// Returns the bitset representing
-    /// the documents that have been deleted.
+    /// Returns the bitset representing the alive `DocId`s.
     pub fn alive_bitset(&self) -> Option<&AliveBitSet> {
         self.alive_bitset_opt.as_ref()
     }
@@ -305,7 +304,7 @@ impl SegmentReader {
     /// as deleted.
     pub fn is_deleted(&self, doc: DocId) -> bool {
         self.alive_bitset()
-            .map(|delete_set| delete_set.is_deleted(doc))
+            .map(|alive_bitset| alive_bitset.is_deleted(doc))
             .unwrap_or(false)
     }
 

src/indexer/index_writer.rs

@@ -158,9 +158,9 @@ pub(crate) fn advance_deletes(
     if num_deleted_docs > num_deleted_docs_before {
         // There are new deletes. We need to write a new delete file.
         segment = segment.with_delete_meta(num_deleted_docs as u32, target_opstamp);
-        let mut delete_file = segment.open_write(SegmentComponent::Delete)?;
-        write_alive_bitset(&alive_bitset, &mut delete_file)?;
-        delete_file.terminate()?;
+        let mut alive_doc_file = segment.open_write(SegmentComponent::Delete)?;
+        write_alive_bitset(&alive_bitset, &mut alive_doc_file)?;
+        alive_doc_file.terminate()?;
     }
 
     segment_entry.set_meta(segment.meta().clone());