fix doc store cache docs (quickwit-oss#1821)

* fix doc store cache docs

addresses an issue reported in quickwit-oss#1820

* rename doc_store_cache_size

src/core/searcher.rs

@@ -249,7 +249,7 @@ impl SearcherInner {
         index: Index,
         segment_readers: Vec<SegmentReader>,
         generation: TrackedObject<SearcherGeneration>,
-        doc_store_cache_size: usize,
+        doc_store_cache_num_blocks: usize,
     ) -> io::Result<SearcherInner> {
         assert_eq!(
             &segment_readers
@@ -261,7 +261,7 @@ impl SearcherInner {
         );
         let store_readers: Vec<StoreReader> = segment_readers
             .iter()
-            .map(|segment_reader| segment_reader.get_store_reader(doc_store_cache_size))
+            .map(|segment_reader| segment_reader.get_store_reader(doc_store_cache_num_blocks))
             .collect::<io::Result<Vec<_>>>()?;
 
         Ok(SearcherInner {

src/core/segment_reader.rs

@@ -134,9 +134,12 @@ impl SegmentReader {
         &self.fieldnorm_readers
     }
 
-    /// Accessor to the segment's `StoreReader`.
-    pub fn get_store_reader(&self, cache_size: usize) -> io::Result<StoreReader> {
-        StoreReader::open(self.store_file.clone(), cache_size)
+    /// Accessor to the segment's [`StoreReader`](crate::store::StoreReader).
+    ///
+    /// `cache_num_blocks` sets the number of decompressed blocks to be cached in an LRU.
+    /// The size of blocks is configurable, this should be reflexted in the
+    pub fn get_store_reader(&self, cache_num_blocks: usize) -> io::Result<StoreReader> {
+        StoreReader::open(self.store_file.clone(), cache_num_blocks)
     }
 
     /// Open a new segment for reading.

src/reader/mod.rs

@@ -44,7 +44,7 @@ pub struct IndexReaderBuilder {
     index: Index,
     warmers: Vec<Weak<dyn Warmer>>,
     num_warming_threads: usize,
-    doc_store_cache_size: usize,
+    doc_store_cache_num_blocks: usize,
 }
 
 impl IndexReaderBuilder {
@@ -55,7 +55,7 @@ impl IndexReaderBuilder {
             index,
             warmers: Vec::new(),
             num_warming_threads: 1,
-            doc_store_cache_size: DOCSTORE_CACHE_CAPACITY,
+            doc_store_cache_num_blocks: DOCSTORE_CACHE_CAPACITY,
         }
     }
 
@@ -72,7 +72,7 @@ impl IndexReaderBuilder {
             searcher_generation_inventory.clone(),
         )?;
         let inner_reader = InnerIndexReader::new(
-            self.doc_store_cache_size,
+            self.doc_store_cache_num_blocks,
             self.index,
             warming_state,
             searcher_generation_inventory,
@@ -119,8 +119,11 @@ impl IndexReaderBuilder {
     ///
     /// The doc store readers cache by default DOCSTORE_CACHE_CAPACITY(100) decompressed blocks.
     #[must_use]
-    pub fn doc_store_cache_size(mut self, doc_store_cache_size: usize) -> IndexReaderBuilder {
-        self.doc_store_cache_size = doc_store_cache_size;
+    pub fn doc_store_cache_num_blocks(
+        mut self,
+        doc_store_cache_num_blocks: usize,
+    ) -> IndexReaderBuilder {
+        self.doc_store_cache_num_blocks = doc_store_cache_num_blocks;
         self
     }
 
@@ -151,7 +154,7 @@ impl TryInto<IndexReader> for IndexReaderBuilder {
 }
 
 struct InnerIndexReader {
-    doc_store_cache_size: usize,
+    doc_store_cache_num_blocks: usize,
     index: Index,
     warming_state: WarmingState,
     searcher: arc_swap::ArcSwap<SearcherInner>,
@@ -161,7 +164,7 @@ struct InnerIndexReader {
 
 impl InnerIndexReader {
     fn new(
-        doc_store_cache_size: usize,
+        doc_store_cache_num_blocks: usize,
         index: Index,
         warming_state: WarmingState,
         // The searcher_generation_inventory is not used as source, but as target to track the
@@ -172,13 +175,13 @@ impl InnerIndexReader {
 
         let searcher = Self::create_searcher(
             &index,
-            doc_store_cache_size,
+            doc_store_cache_num_blocks,
             &warming_state,
             &searcher_generation_counter,
             &searcher_generation_inventory,
         )?;
         Ok(InnerIndexReader {
-            doc_store_cache_size,
+            doc_store_cache_num_blocks,
             index,
             warming_state,
             searcher: ArcSwap::from(searcher),
@@ -214,7 +217,7 @@ impl InnerIndexReader {
 
     fn create_searcher(
         index: &Index,
-        doc_store_cache_size: usize,
+        doc_store_cache_num_blocks: usize,
         warming_state: &WarmingState,
         searcher_generation_counter: &Arc<AtomicU64>,
         searcher_generation_inventory: &Inventory<SearcherGeneration>,
@@ -232,7 +235,7 @@ impl InnerIndexReader {
             index.clone(),
             segment_readers,
             searcher_generation,
-            doc_store_cache_size,
+            doc_store_cache_num_blocks,
         )?);
 
         warming_state.warm_new_searcher_generation(&searcher.clone().into())?;
@@ -242,7 +245,7 @@ impl InnerIndexReader {
     fn reload(&self) -> crate::Result<()> {
         let searcher = Self::create_searcher(
             &self.index,
-            self.doc_store_cache_size,
+            self.doc_store_cache_num_blocks,
             &self.warming_state,
             &self.searcher_generation_counter,
             &self.searcher_generation_inventory,

src/store/mod.rs

@@ -4,8 +4,8 @@
 //! order to be handled in the `Store`.
 //!
 //! Internally, documents (or rather their stored fields) are serialized to a buffer.
-//! When the buffer exceeds 16K, the buffer is compressed using `brotli`, `LZ4` or `snappy`
-//! and the resulting block is written to disk.
+//! When the buffer exceeds `block_size` (defaults to 16K), the buffer is compressed using `brotli`,
+//! `LZ4` or `snappy` and the resulting block is written to disk.
 //!
 //! One can then request for a specific `DocId`.
 //! A skip list helps navigating to the right block,
@@ -28,8 +28,6 @@
 //! - at the segment level, the
 //! [`SegmentReader`'s `doc` method](../struct.SegmentReader.html#method.doc)
 //! - at the index level, the [`Searcher::doc()`](crate::Searcher::doc) method
-//!
-//! !
 
 mod compressors;
 mod decompressors;

src/store/reader.rs

@@ -114,7 +114,10 @@ impl Sum for CacheStats {
 
 impl StoreReader {
     /// Opens a store reader
-    pub fn open(store_file: FileSlice, cache_size: usize) -> io::Result<StoreReader> {
+    ///
+    /// `cache_num_blocks` sets the number of decompressed blocks to be cached in an LRU.
+    /// The size of blocks is configurable, this should be reflexted in the
+    pub fn open(store_file: FileSlice, cache_num_blocks: usize) -> io::Result<StoreReader> {
         let (footer, data_and_offset) = DocStoreFooter::extract_footer(store_file)?;
 
         let (data_file, offset_index_file) = data_and_offset.split(footer.offset as usize);
@@ -125,8 +128,8 @@ impl StoreReader {
             decompressor: footer.decompressor,
             data: data_file,
             cache: BlockCache {
-                cache: NonZeroUsize::new(cache_size)
-                    .map(|cache_size| Mutex::new(LruCache::new(cache_size))),
+                cache: NonZeroUsize::new(cache_num_blocks)
+                    .map(|cache_num_blocks| Mutex::new(LruCache::new(cache_num_blocks))),
                 cache_hits: Default::default(),
                 cache_misses: Default::default(),
             },