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reader.rs
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reader.rs
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use std::io;
use std::iter::Sum;
use std::ops::AddAssign;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::{Arc, Mutex};
use common::{BinarySerializable, HasLen, VInt};
use lru::LruCache;
use ownedbytes::OwnedBytes;
use super::footer::DocStoreFooter;
use super::index::SkipIndex;
use super::Decompressor;
use crate::directory::FileSlice;
use crate::error::DataCorruption;
use crate::fastfield::AliveBitSet;
use crate::schema::Document;
use crate::space_usage::StoreSpaceUsage;
use crate::store::index::Checkpoint;
use crate::DocId;
pub(crate) const DOCSTORE_CACHE_CAPACITY: usize = 100;
type Block = OwnedBytes;
/// Reads document off tantivy's [`Store`](./index.html)
pub struct StoreReader {
decompressor: Decompressor,
data: FileSlice,
skip_index: Arc<SkipIndex>,
space_usage: StoreSpaceUsage,
cache: BlockCache,
}
/// The cache for decompressed blocks.
struct BlockCache {
cache: Mutex<LruCache<usize, Block>>,
cache_hits: Arc<AtomicUsize>,
cache_misses: Arc<AtomicUsize>,
}
impl BlockCache {
fn get_from_cache(&self, pos: usize) -> Option<Block> {
if let Some(block) = self.cache.lock().unwrap().get(&pos) {
self.cache_hits.fetch_add(1, Ordering::SeqCst);
return Some(block.clone());
}
self.cache_misses.fetch_add(1, Ordering::SeqCst);
None
}
fn put_into_cache(&self, pos: usize, data: Block) {
self.cache.lock().unwrap().put(pos, data);
}
fn stats(&self) -> CacheStats {
CacheStats {
cache_hits: self.cache_hits.load(Ordering::Relaxed),
cache_misses: self.cache_misses.load(Ordering::Relaxed),
num_entries: self.len(),
}
}
fn len(&self) -> usize {
self.cache.lock().unwrap().len()
}
#[cfg(test)]
fn peek_lru(&self) -> Option<usize> {
self.cache
.lock()
.unwrap()
.peek_lru()
.map(|(&k, _)| k as usize)
}
}
#[derive(Debug, Default)]
/// CacheStats for the `StoreReader`.
pub struct CacheStats {
/// The number of entries in the cache
pub num_entries: usize,
/// The number of cache hits.
pub cache_hits: usize,
/// The number of cache misses.
pub cache_misses: usize,
}
impl AddAssign for CacheStats {
fn add_assign(&mut self, other: Self) {
*self = Self {
num_entries: self.num_entries + other.num_entries,
cache_hits: self.cache_hits + other.cache_hits,
cache_misses: self.cache_misses + other.cache_misses,
};
}
}
impl Sum for CacheStats {
fn sum<I: Iterator<Item = Self>>(mut iter: I) -> Self {
let mut first = iter.next().unwrap_or_default();
for el in iter {
first += el;
}
first
}
}
impl StoreReader {
/// Opens a store reader
pub fn open(store_file: FileSlice, cache_size: 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);
let index_data = offset_index_file.read_bytes()?;
let space_usage = StoreSpaceUsage::new(data_file.len(), offset_index_file.len());
let skip_index = SkipIndex::open(index_data);
Ok(StoreReader {
decompressor: footer.decompressor,
data: data_file,
cache: BlockCache {
cache: Mutex::new(LruCache::new(cache_size)),
cache_hits: Default::default(),
cache_misses: Default::default(),
},
skip_index: Arc::new(skip_index),
space_usage,
})
}
pub(crate) fn block_checkpoints(&self) -> impl Iterator<Item = Checkpoint> + '_ {
self.skip_index.checkpoints()
}
pub(crate) fn decompressor(&self) -> Decompressor {
self.decompressor
}
/// Returns the cache hit and miss statistics of the store reader.
pub(crate) fn cache_stats(&self) -> CacheStats {
self.cache.stats()
}
/// Get checkpoint for DocId. The checkpoint can be used to load a block containing the
/// document.
///
/// Advanced API. In most cases use [get](Self::get).
fn block_checkpoint(&self, doc_id: DocId) -> crate::Result<Checkpoint> {
self.skip_index.seek(doc_id).ok_or_else(|| {
crate::TantivyError::InvalidArgument(format!("Failed to lookup Doc #{}.", doc_id))
})
}
pub(crate) fn block_data(&self) -> io::Result<OwnedBytes> {
self.data.read_bytes()
}
fn get_compressed_block(&self, checkpoint: &Checkpoint) -> io::Result<OwnedBytes> {
self.data.slice(checkpoint.byte_range.clone()).read_bytes()
}
/// Loads and decompresses a block.
///
/// Advanced API. In most cases use [get](Self::get).
fn read_block(&self, checkpoint: &Checkpoint) -> io::Result<Block> {
let cache_key = checkpoint.byte_range.start;
if let Some(block) = self.cache.get_from_cache(cache_key) {
return Ok(block);
}
let compressed_block = self.get_compressed_block(checkpoint)?;
let decompressed_block =
OwnedBytes::new(self.decompressor.decompress(compressed_block.as_ref())?);
self.cache
.put_into_cache(cache_key, decompressed_block.clone());
Ok(decompressed_block)
}
/// Reads a given document.
///
/// Calling `.get(doc)` is relatively costly as it requires
/// decompressing a compressed block. The store utilizes a LRU cache,
/// so accessing docs from the same compressed block should be faster.
/// For that reason a store reader should be kept and reused.
///
/// It should not be called to score documents
/// for instance.
pub fn get(&self, doc_id: DocId) -> crate::Result<Document> {
let mut doc_bytes = self.get_document_bytes(doc_id)?;
Ok(Document::deserialize(&mut doc_bytes)?)
}
/// Returns raw bytes of a given document.
///
/// Calling `.get(doc)` is relatively costly as it requires
/// decompressing a compressed block. The store utilizes a LRU cache,
/// so accessing docs from the same compressed block should be faster.
/// For that reason a store reader should be kept and reused.
pub fn get_document_bytes(&self, doc_id: DocId) -> crate::Result<OwnedBytes> {
let checkpoint = self.block_checkpoint(doc_id)?;
let block = self.read_block(&checkpoint)?;
Self::get_document_bytes_from_block(block, doc_id, &checkpoint)
}
/// Advanced API.
///
/// In most cases use [get_document_bytes](Self::get_document_bytes).
fn get_document_bytes_from_block(
block: OwnedBytes,
doc_id: DocId,
checkpoint: &Checkpoint,
) -> crate::Result<OwnedBytes> {
let mut cursor = &block[..];
let cursor_len_before = cursor.len();
for _ in checkpoint.doc_range.start..doc_id {
let doc_length = VInt::deserialize(&mut cursor)?.val() as usize;
cursor = &cursor[doc_length..];
}
let doc_length = VInt::deserialize(&mut cursor)?.val() as usize;
let start_pos = cursor_len_before - cursor.len();
let end_pos = cursor_len_before - cursor.len() + doc_length;
Ok(block.slice(start_pos..end_pos))
}
/// Iterator over all Documents in their order as they are stored in the doc store.
/// Use this, if you want to extract all Documents from the doc store.
/// The alive_bitset has to be forwarded from the `SegmentReader` or the results maybe wrong.
pub fn iter<'a: 'b, 'b>(
&'b self,
alive_bitset: Option<&'a AliveBitSet>,
) -> impl Iterator<Item = crate::Result<Document>> + 'b {
self.iter_raw(alive_bitset).map(|doc_bytes_res| {
let mut doc_bytes = doc_bytes_res?;
Ok(Document::deserialize(&mut doc_bytes)?)
})
}
/// Iterator over all RawDocuments in their order as they are stored in the doc store.
/// Use this, if you want to extract all Documents from the doc store.
/// The alive_bitset has to be forwarded from the `SegmentReader` or the results maybe wrong.
pub(crate) fn iter_raw<'a: 'b, 'b>(
&'b self,
alive_bitset: Option<&'a AliveBitSet>,
) -> impl Iterator<Item = crate::Result<OwnedBytes>> + 'b {
let last_doc_id = self
.block_checkpoints()
.last()
.map(|checkpoint| checkpoint.doc_range.end)
.unwrap_or(0);
let mut checkpoint_block_iter = self.block_checkpoints();
let mut curr_checkpoint = checkpoint_block_iter.next();
let mut curr_block = curr_checkpoint
.as_ref()
.map(|checkpoint| self.read_block(checkpoint).map_err(|e| e.kind())); // map error in order to enable cloning
let mut block_start_pos = 0;
let mut num_skipped = 0;
let mut reset_block_pos = false;
(0..last_doc_id)
.filter_map(move |doc_id| {
// filter_map is only used to resolve lifetime issues between the two closures on
// the outer variables
// check move to next checkpoint
if doc_id >= curr_checkpoint.as_ref().unwrap().doc_range.end {
curr_checkpoint = checkpoint_block_iter.next();
curr_block = curr_checkpoint
.as_ref()
.map(|checkpoint| self.read_block(checkpoint).map_err(|e| e.kind()));
reset_block_pos = true;
num_skipped = 0;
}
let alive = alive_bitset.map_or(true, |bitset| bitset.is_alive(doc_id));
if alive {
let ret = Some((curr_block.clone(), num_skipped, reset_block_pos));
// the map block will move over the num_skipped, so we reset to 0
num_skipped = 0;
reset_block_pos = false;
ret
} else {
// we keep the number of skipped documents to move forward in the map block
num_skipped += 1;
None
}
})
.map(move |(block, num_skipped, reset_block_pos)| {
let block = block
.ok_or_else(|| {
DataCorruption::comment_only(
"the current checkpoint in the doc store iterator is none, this \
should never happen",
)
})?
.map_err(|error_kind| {
std::io::Error::new(error_kind, "error when reading block in doc store")
})?;
// this flag is set, when filter_map moved to the next block
if reset_block_pos {
block_start_pos = 0;
}
let mut cursor = &block[block_start_pos..];
let mut pos = 0;
// move forward 1 doc + num_skipped in block and return length of current doc
let doc_length = loop {
let doc_length = VInt::deserialize(&mut cursor)?.val() as usize;
let num_bytes_read = block[block_start_pos..].len() - cursor.len();
block_start_pos += num_bytes_read;
pos += 1;
if pos == num_skipped + 1 {
break doc_length;
} else {
block_start_pos += doc_length;
cursor = &block[block_start_pos..];
}
};
let end_pos = block_start_pos + doc_length;
let doc_bytes = block.slice(block_start_pos..end_pos);
block_start_pos = end_pos;
Ok(doc_bytes)
})
}
/// Summarize total space usage of this store reader.
pub fn space_usage(&self) -> StoreSpaceUsage {
self.space_usage.clone()
}
}
#[cfg(feature = "quickwit")]
impl StoreReader {
/// Advanced API.
///
/// In most cases use [get_async](Self::get_async)
///
/// Loads and decompresses a block asynchronously.
async fn read_block_async(&self, checkpoint: &Checkpoint) -> crate::AsyncIoResult<Block> {
let cache_key = checkpoint.byte_range.start;
if let Some(block) = self.cache.get_from_cache(checkpoint.byte_range.start) {
return Ok(block.clone());
}
let compressed_block = self
.data
.slice(checkpoint.byte_range.clone())
.read_bytes_async()
.await?;
let decompressed_block =
OwnedBytes::new(self.decompressor.decompress(compressed_block.as_ref())?);
self.cache
.put_into_cache(cache_key, decompressed_block.clone());
Ok(decompressed_block)
}
/// Fetches a document asynchronously.
pub async fn get_document_bytes_async(&self, doc_id: DocId) -> crate::Result<OwnedBytes> {
let checkpoint = self.block_checkpoint(doc_id)?;
let block = self.read_block_async(&checkpoint).await?;
Self::get_document_bytes_from_block(block, doc_id, &checkpoint)
}
/// Reads raw bytes of a given document. Async version of [get](Self::get).
pub async fn get_async(&self, doc_id: DocId) -> crate::Result<Document> {
let mut doc_bytes = self.get_document_bytes_async(doc_id).await?;
Ok(Document::deserialize(&mut doc_bytes)?)
}
}
#[cfg(test)]
mod tests {
use std::path::Path;
use super::*;
use crate::directory::RamDirectory;
use crate::schema::{Document, Field};
use crate::store::tests::write_lorem_ipsum_store;
use crate::store::Compressor;
use crate::Directory;
const BLOCK_SIZE: usize = 16_384;
fn get_text_field<'a>(doc: &'a Document, field: &'a Field) -> Option<&'a str> {
doc.get_first(*field).and_then(|f| f.as_text())
}
#[test]
fn test_store_lru_cache() -> crate::Result<()> {
let directory = RamDirectory::create();
let path = Path::new("store");
let writer = directory.open_write(path)?;
let schema = write_lorem_ipsum_store(writer, 500, Compressor::default(), BLOCK_SIZE);
let title = schema.get_field("title").unwrap();
let store_file = directory.open_read(path)?;
let store = StoreReader::open(store_file, DOCSTORE_CACHE_CAPACITY)?;
assert_eq!(store.cache.len(), 0);
assert_eq!(store.cache_stats().cache_hits, 0);
assert_eq!(store.cache_stats().cache_misses, 0);
let doc = store.get(0)?;
assert_eq!(get_text_field(&doc, &title), Some("Doc 0"));
assert_eq!(store.cache.len(), 1);
assert_eq!(store.cache_stats().cache_hits, 0);
assert_eq!(store.cache_stats().cache_misses, 1);
assert_eq!(store.cache.peek_lru(), Some(0));
let doc = store.get(499)?;
assert_eq!(get_text_field(&doc, &title), Some("Doc 499"));
assert_eq!(store.cache.len(), 2);
assert_eq!(store.cache_stats().cache_hits, 0);
assert_eq!(store.cache_stats().cache_misses, 2);
assert_eq!(store.cache.peek_lru(), Some(0));
let doc = store.get(0)?;
assert_eq!(get_text_field(&doc, &title), Some("Doc 0"));
assert_eq!(store.cache.len(), 2);
assert_eq!(store.cache_stats().cache_hits, 1);
assert_eq!(store.cache_stats().cache_misses, 2);
assert_eq!(store.cache.peek_lru(), Some(9210));
Ok(())
}
}