allow warming partially an sstable for an automaton

Cargo.toml

@@ -66,6 +66,7 @@ tokenizer-api = { version = "0.3", path = "./tokenizer-api", package = "tantivy-
 sketches-ddsketch = { version = "0.3.0", features = ["use_serde"] }
 hyperloglogplus = { version = "0.4.1", features = ["const-loop"] }
 futures-util = { version = "0.3.28", optional = true }
+futures-channel = { version = "0.3.28", optional = true }
 fnv = "1.0.7"
 
 [target.'cfg(windows)'.dependencies]
@@ -120,7 +121,7 @@ zstd-compression = ["zstd"]
 failpoints = ["fail", "fail/failpoints"]
 unstable = []                            # useful for benches.
 
-quickwit = ["sstable", "futures-util"]
+quickwit = ["sstable", "futures-util", "futures-channel"]
 
 # Compares only the hash of a string when indexing data.
 # Increases indexing speed, but may lead to extremely rare missing terms, when there's a hash collision.

src/index/inverted_index_reader.rs

@@ -3,6 +3,12 @@ use std::io;
 use common::json_path_writer::JSON_END_OF_PATH;
 use common::BinarySerializable;
 use fnv::FnvHashSet;
+#[cfg(feature = "quickwit")]
+use futures_util::{FutureExt, StreamExt, TryStreamExt};
+#[cfg(feature = "quickwit")]
+use itertools::Itertools;
+#[cfg(feature = "quickwit")]
+use tantivy_fst::automaton::{AlwaysMatch, Automaton};
 
 use crate::directory::FileSlice;
 use crate::positions::PositionReader;
@@ -219,13 +225,18 @@ impl InvertedIndexReader {
         self.termdict.get_async(term.serialized_value_bytes()).await
     }
 
-    async fn get_term_range_async(
-        &self,
+    async fn get_term_range_async<'a, A: Automaton + 'a>(
+        &'a self,
         terms: impl std::ops::RangeBounds<Term>,
+        automaton: A,
         limit: Option<u64>,
-    ) -> io::Result<impl Iterator<Item = TermInfo> + '_> {
+        merge_holes_under_bytes: usize,
+    ) -> io::Result<impl Iterator<Item = TermInfo> + 'a>
+    where
+        A::State: Clone,
+    {
         use std::ops::Bound;
-        let range_builder = self.termdict.range();
+        let range_builder = self.termdict.search(automaton);
         let range_builder = match terms.start_bound() {
             Bound::Included(bound) => range_builder.ge(bound.serialized_value_bytes()),
             Bound::Excluded(bound) => range_builder.gt(bound.serialized_value_bytes()),
@@ -242,7 +253,9 @@ impl InvertedIndexReader {
             range_builder
         };
 
-        let mut stream = range_builder.into_stream_async().await?;
+        let mut stream = range_builder
+            .into_stream_async_merging_holes(merge_holes_under_bytes)
+            .await?;
 
         let iter = std::iter::from_fn(move || stream.next().map(|(_k, v)| v.clone()));
 
@@ -288,7 +301,9 @@ impl InvertedIndexReader {
         limit: Option<u64>,
         with_positions: bool,
     ) -> io::Result<bool> {
-        let mut term_info = self.get_term_range_async(terms, limit).await?;
+        let mut term_info = self
+            .get_term_range_async(terms, AlwaysMatch, limit, 0)
+            .await?;
 
         let Some(first_terminfo) = term_info.next() else {
             // no key matches, nothing more to load
@@ -315,6 +330,83 @@ impl InvertedIndexReader {
         Ok(true)
     }
 
+    /// Warmup a block postings given a range of `Term`s.
+    /// This method is for an advanced usage only.
+    ///
+    /// returns a boolean, whether a term matching the range was found in the dictionary
+    pub async fn warm_postings_automaton<
+        A: Automaton + Clone + Send + 'static,
+        E: FnOnce(Box<dyn FnOnce() -> io::Result<()> + Send>) -> F,
+        F: std::future::Future<Output = io::Result<()>>,
+    >(
+        &self,
+        automaton: A,
+        // with_positions: bool, at the moment we have no use for it, and supporting it would add
+        // complexity to the coalesce
+        executor: E,
+    ) -> io::Result<bool>
+    where
+        A::State: Clone,
+    {
+        // merge holes under 4MiB, that's how many bytes we can hope to receive during a TTFB from
+        // S3 (~80MiB/s, and 50ms latency)
+        const MERGE_HOLES_UNDER_BYTES: usize = (80 * 1024 * 1024 * 50) / 1000;
+        // we build a first iterator to download everything. Simply calling the function already
+        // download everything we need from the sstable, but doesn't start iterating over it.
+        let _term_info_iter = self
+            .get_term_range_async(.., automaton.clone(), None, MERGE_HOLES_UNDER_BYTES)
+            .await?;
+
+        let (sender, posting_ranges_to_load_stream) = futures_channel::mpsc::unbounded();
+        let termdict = self.termdict.clone();
+        let cpu_bound_task = move || {
+            // then we build a 2nd iterator, this one with no holes, so we don't go through blocks
+            // we can't match.
+            // This makes the assumption there is a caching layer below us, which gives sync read
+            // for free after the initial async access. This might not always be true, but is in
+            // Quickwit.
+            // We build things from this closure otherwise we get into lifetime issues that can only
+            // be solved with self referential strucs. Returning an io::Result from here is a bit
+            // more leaky abstraction-wise, but a lot better than the alternative
+            let mut stream = termdict.search(automaton).into_stream()?;
+
+            // we could do without an iterator, but this allows us access to coalesce which simplify
+            // things
+            let posting_ranges_iter =
+                std::iter::from_fn(move || stream.next().map(|(_k, v)| v.postings_range.clone()))
+                    .coalesce(|range1, range2| {
+                        if range1.end + MERGE_HOLES_UNDER_BYTES >= range2.start {
+                            Ok(range1.start..range2.end)
+                        } else {
+                            Err((range1, range2))
+                        }
+                    });
+
+            for posting_range in posting_ranges_iter {
+                if let Err(_) = sender.unbounded_send(posting_range) {
+                    // this should happen only when search is cancelled
+                    return Err(io::Error::other("failed to send posting range back"));
+                }
+            }
+            Ok(())
+        };
+        let task_handle = executor(Box::new(cpu_bound_task));
+
+        let posting_downloader = posting_ranges_to_load_stream
+            .map(|posting_slice| {
+                self.postings_file_slice
+                    .read_bytes_slice_async(posting_slice)
+                    .map(|result| result.map(|_slice| ()))
+            })
+            .buffer_unordered(5)
+            .try_collect::<Vec<()>>();
+
+        let (_, slices_downloaded) =
+            futures_util::future::try_join(task_handle, posting_downloader).await?;
+
+        Ok(!slices_downloaded.is_empty())
+    }
+
     /// Warmup the block postings for all terms.
     /// This method is for an advanced usage only.
     ///

src/termdict/mod.rs

@@ -74,6 +74,7 @@ const CURRENT_TYPE: DictionaryType = DictionaryType::SSTable;
 
 // TODO in the future this should become an enum of supported dictionaries
 /// A TermDictionary wrapping either an FST based dictionary or a SSTable based one.
+#[cfg_attr(feature = "quickwit", derive(Clone))]
 pub struct TermDictionary(InnerTermDict);
 
 impl TermDictionary {

src/termdict/sstable_termdict/mod.rs

@@ -28,6 +28,7 @@ pub type TermDictionaryBuilder<W> = sstable::Writer<W, TermInfoValueWriter>;
 pub type TermStreamer<'a, A = AlwaysMatch> = sstable::Streamer<'a, TermSSTable, A>;
 
 /// SSTable used to store TermInfo objects.
+#[derive(Clone)]
 pub struct TermSSTable;
 
 pub type TermStreamerBuilder<'a, A = AlwaysMatch> = sstable::StreamerBuilder<'a, TermSSTable, A>;

sstable/Cargo.toml

@@ -11,6 +11,8 @@ description = "sstables for tantivy"
 
 [dependencies]
 common = {version= "0.7", path="../common", package="tantivy-common"}
+futures-util = "0.3.30"
+itertools = "0.13.0"
 tantivy-bitpacker = { version= "0.6", path="../bitpacker" }
 tantivy-fst = "0.5"
 # experimental gives us access to Decompressor::upper_bound