fix columnar tests

columnar/src/tests.rs

@@ -26,7 +26,7 @@ fn test_dataframe_writer_str() {
     assert_eq!(columnar.num_columns(), 1);
     let cols: Vec<DynamicColumnHandle> = columnar.read_columns("my_string").unwrap();
     assert_eq!(cols.len(), 1);
-    assert_eq!(cols[0].num_bytes(), 87);
+    assert_eq!(cols[0].num_bytes(), 99);
 }
 
 #[test]
@@ -40,7 +40,7 @@ fn test_dataframe_writer_bytes() {
     assert_eq!(columnar.num_columns(), 1);
     let cols: Vec<DynamicColumnHandle> = columnar.read_columns("my_string").unwrap();
     assert_eq!(cols.len(), 1);
-    assert_eq!(cols[0].num_bytes(), 87);
+    assert_eq!(cols[0].num_bytes(), 99);
 }
 
 #[test]

ownedbytes/src/lib.rs

@@ -1,5 +1,5 @@
 use std::convert::TryInto;
-use std::ops::{Deref, Range};
+use std::ops::Deref;
 use std::sync::Arc;
 use std::{fmt, io};
 
@@ -37,7 +37,7 @@ impl OwnedBytes {
     /// creates a fileslice that is just a view over a slice of the data.
     #[must_use]
     #[inline]
-    pub fn slice(&self, range: Range<usize>) -> Self {
+    pub fn slice(&self, range: impl std::slice::SliceIndex<[u8], Output = [u8]>) -> Self {
         OwnedBytes {
             data: &self.data[range],
             box_stable_deref: self.box_stable_deref.clone(),

src/fastfield/mod.rs

@@ -131,7 +131,7 @@ mod tests {
         }
         let file = directory.open_read(path).unwrap();
 
-        assert_eq!(file.len(), 93);
+        assert_eq!(file.len(), 105);
         let fast_field_readers = FastFieldReaders::open(file, SCHEMA.clone()).unwrap();
         let column = fast_field_readers
             .u64("field")
@@ -181,7 +181,7 @@ mod tests {
             write.terminate().unwrap();
         }
         let file = directory.open_read(path).unwrap();
-        assert_eq!(file.len(), 121);
+        assert_eq!(file.len(), 133);
         let fast_field_readers = FastFieldReaders::open(file, SCHEMA.clone()).unwrap();
         let col = fast_field_readers
             .u64("field")
@@ -214,7 +214,7 @@ mod tests {
             write.terminate().unwrap();
         }
         let file = directory.open_read(path).unwrap();
-        assert_eq!(file.len(), 94);
+        assert_eq!(file.len(), 106);
         let fast_field_readers = FastFieldReaders::open(file, SCHEMA.clone()).unwrap();
         let fast_field_reader = fast_field_readers
             .u64("field")
@@ -246,7 +246,7 @@ mod tests {
             write.terminate().unwrap();
         }
         let file = directory.open_read(path).unwrap();
-        assert_eq!(file.len(), 4489);
+        assert_eq!(file.len(), 4501);
         {
             let fast_field_readers = FastFieldReaders::open(file, SCHEMA.clone()).unwrap();
             let col = fast_field_readers
@@ -279,7 +279,7 @@ mod tests {
             write.terminate().unwrap();
         }
         let file = directory.open_read(path).unwrap();
-        assert_eq!(file.len(), 265);
+        assert_eq!(file.len(), 277);
 
         {
             let fast_field_readers = FastFieldReaders::open(file, schema).unwrap();
@@ -773,7 +773,7 @@ mod tests {
             write.terminate().unwrap();
         }
         let file = directory.open_read(path).unwrap();
-        assert_eq!(file.len(), 102);
+        assert_eq!(file.len(), 114);
         let fast_field_readers = FastFieldReaders::open(file, schema).unwrap();
         let bool_col = fast_field_readers.bool("field_bool").unwrap();
         assert_eq!(bool_col.first(0), Some(true));
@@ -805,7 +805,7 @@ mod tests {
             write.terminate().unwrap();
         }
         let file = directory.open_read(path).unwrap();
-        assert_eq!(file.len(), 114);
+        assert_eq!(file.len(), 126);
         let readers = FastFieldReaders::open(file, schema).unwrap();
         let bool_col = readers.bool("field_bool").unwrap();
         for i in 0..25 {
@@ -830,7 +830,7 @@ mod tests {
             write.terminate().unwrap();
         }
         let file = directory.open_read(path).unwrap();
-        assert_eq!(file.len(), 104);
+        assert_eq!(file.len(), 116);
         let fastfield_readers = FastFieldReaders::open(file, schema).unwrap();
         let col = fastfield_readers.bool("field_bool").unwrap();
         assert_eq!(col.first(0), None);

sstable/README.md

@@ -89,15 +89,21 @@ Note: as the SSTable does not support redundant keys, there is no ambiguity betw
 
 ### SSTFooter
 ```
-+-------+-------+-----+-------------+---------+---------+
++-------+-------+-----+------------------+------------+-------------+---------+---------+
-| Block | Block | ... | IndexOffset | NumTerm | Version |
+| Block | Block | ... | FirstLayerOffset | LayerCount | IndexOffset | NumTerm | Version |
-+-------+-------+-----+-------------+---------+---------+
++-------+-------+-----+------------------+------------+-------------+---------+---------+
-|----( # of blocks)---|
+|----(# of blocks)----|
 ```
 - Block(SSTBlock): uses IndexValue for its Values format
+- FirstLayerOffset(u64): Offset between the start of the footer and the start of the top level index
+- LayerCount(u32): Number of layers of index (min 1) ## TODO do we want to use 0 as a marker for no layers? It makes small sstables 12 bytes more compact (the 0u32 would alias with the "end of sstable marker")
 - IndexOffset(u64): Offset to the start of the SSTFooter
 - NumTerm(u64): number of terms in the sstable
-- Version(u32): Currently equal to 2
+- Version(u32): Currently equal to 3
+
+Blocks referencing the main table and block referencing the index itself are encoded the same way and
+are not directly differentiated. Offsets in blocks referencing the index are relative to the start of
+the footer, blocks referencing the main table are relative to the start of that table.
 
 ### IndexValue
 ```

sstable/src/delta.rs

@@ -20,6 +20,7 @@ where W: io::Write
     // Only here to avoid allocations.
     stateless_buffer: Vec<u8>,
     block_len: usize,
+    compress: bool,
 }
 
 impl<W, TValueWriter> DeltaWriter<W, TValueWriter>
@@ -34,6 +35,18 @@ where
             value_writer: TValueWriter::default(),
             stateless_buffer: Vec::new(),
             block_len: BLOCK_LEN,
+            compress: true,
+        }
+    }
+
+    pub fn new_no_compression(wrt: W) -> Self {
+        DeltaWriter {
+            block: Vec::with_capacity(BLOCK_LEN * 2),
+            write: CountingWriter::wrap(BufWriter::new(wrt)),
+            value_writer: TValueWriter::default(),
+            stateless_buffer: Vec::new(),
+            block_len: BLOCK_LEN,
+            compress: false,
         }
     }
 
@@ -53,7 +66,7 @@ where
 
         let block_len = buffer.len() + self.block.len();
 
-        if block_len > 2048 {
+        if block_len > 2048 && self.compress {
             buffer.extend_from_slice(&self.block);
             self.block.clear();
 

sstable/src/dictionary.rs

@@ -128,52 +128,86 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
         key_range: impl RangeBounds<[u8]>,
         limit: Option<u64>,
     ) -> FileSlice {
-        let first_block_id = match key_range.start_bound() {
+        // we don't perform great when limit is set to a large value, and sometime we use u64::MAX
-            Bound::Included(key) | Bound::Excluded(key) => {
+        // as a marker for no limit, so we'd better capture that.
-                let Some(first_block_id) = self.sstable_index.locate_with_key(key) else {
+        // (not great means we decode up to the whole bottom layer index, which can take dozens of
-                    return FileSlice::empty();
+        // ms on a 100m term dictionary)
-                };
+        let limit = limit.filter(|limit| *limit != u64::MAX);
-                Some(first_block_id)
+
-            }
+        // TODO replace unwraps with proper error handling
+        let start_key = match key_range.start_bound() {
+            Bound::Included(key) | Bound::Excluded(key) => key,
+            Bound::Unbounded => &[],
+        };
+        let end_key = match key_range.end_bound() {
+            Bound::Included(key) | Bound::Excluded(key) => Some(key),
             Bound::Unbounded => None,
         };
-
+        let bounds = if let Some(limit) = limit {
-        let last_block_id = match key_range.end_bound() {
+            let mut sstable_iterator = self.sstable_index.iterate_from_key(start_key).unwrap();
-            Bound::Included(key) | Bound::Excluded(key) => self.sstable_index.locate_with_key(key),
+            let Some(start_block) = sstable_iterator.value() else {
-            Bound::Unbounded => None,
+                // range_start is after end of table
-        };
-
-        let start_bound = if let Some(first_block_id) = first_block_id {
-            let Some(block_addr) = self.sstable_index.get_block(first_block_id) else {
                 return FileSlice::empty();
             };
-            Bound::Included(block_addr.byte_range.start)
+            if let Some(end_key) = end_key {
-        } else {
+                if sstable_iterator.key().unwrap() >= end_key {
-            Bound::Unbounded
+                    // the start and end keys are in the same block, return just that block
-        };
+                    return self.sstable_slice.slice(start_block.byte_range.clone());
+                }
+            }
+            let start_bound = start_block.byte_range.start;
 
-        let last_block_id = if let Some(limit) = limit {
+            sstable_iterator.advance().unwrap();
-            let second_block_id = first_block_id.map(|id| id + 1).unwrap_or(0);
+            let Some(second_block) = sstable_iterator.value() else {
-            if let Some(block_addr) = self.sstable_index.get_block(second_block_id) {
+                // we reached the end of the sstable, return everything from start_bound
-                let ordinal_limit = block_addr.first_ordinal + limit;
+                return self.sstable_slice.slice(start_bound..);
-                let last_block_limit = self.sstable_index.locate_with_ord(ordinal_limit);
+            };
-                if let Some(last_block_id) = last_block_id {
+            let mut end_bound = second_block.byte_range.end;
-                    Some(last_block_id.min(last_block_limit))
+            if let Some(end_key) = end_key {
+                if sstable_iterator.key().unwrap() >= end_key {
+                    return self.sstable_slice.slice(start_bound..end_bound);
+                }
+            }
+
+            let target_ord = second_block.first_ordinal + limit;
+
+            while sstable_iterator.advance().unwrap() {
+                let block = sstable_iterator.value().unwrap();
+                if block.first_ordinal >= target_ord {
+                    break;
+                }
+                end_bound = block.byte_range.end;
+                if let Some(end_key) = end_key {
+                    if sstable_iterator.key().unwrap() >= end_key {
+                        break;
+                    }
+                }
+            }
+
+            let start_bound = Bound::Included(start_bound);
+            let end_bound = Bound::Excluded(end_bound);
+
+            (start_bound, end_bound)
+        } else {
+            let Some(start_block) = self.sstable_index.get_block_with_key(start_key).unwrap()
+            else {
+                // range_start is after end of table
+                return FileSlice::empty();
+            };
+            let start_bound = Bound::Included(start_block.byte_range.start);
+            let end_bound = if let Some(end_key) = end_key {
+                if let Some(end_block) = self.sstable_index.get_block_with_key(end_key).unwrap() {
+                    Bound::Excluded(end_block.byte_range.end)
                 } else {
-                    Some(last_block_limit)
+                    Bound::Unbounded
                 }
             } else {
-                last_block_id
+                Bound::Unbounded
-            }
+            };
-        } else {
+            (start_bound, end_bound)
-            last_block_id
         };
-        let end_bound = last_block_id
-            .and_then(|block_id| self.sstable_index.get_block(block_id))
-            .map(|block_addr| Bound::Excluded(block_addr.byte_range.end))
-            .unwrap_or(Bound::Unbounded);
 
-        self.sstable_slice.slice((start_bound, end_bound))
+        self.sstable_slice.slice(bounds)
     }
 
     /// Opens a `TermDictionary`.
@@ -181,29 +215,57 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
         let (main_slice, footer_len_slice) = term_dictionary_file.split_from_end(20);
         let mut footer_len_bytes: OwnedBytes = footer_len_slice.read_bytes()?;
 
+        // let layer_count = u32::deserialize(&mut footer_len_bytes)?;
         let index_offset = u64::deserialize(&mut footer_len_bytes)?;
         let num_terms = u64::deserialize(&mut footer_len_bytes)?;
         let version = u32::deserialize(&mut footer_len_bytes)?;
-        if version != crate::SSTABLE_VERSION {
-            return Err(io::Error::new(
-                io::ErrorKind::Other,
-                format!(
-                    "Unsuported sstable version, expected {version}, found {}",
-                    crate::SSTABLE_VERSION,
-                ),
-            ));
-        }
-
         let (sstable_slice, index_slice) = main_slice.split(index_offset as usize);
-        let sstable_index_bytes = index_slice.read_bytes()?;
+        match version {
-        let sstable_index = SSTableIndex::load(sstable_index_bytes)
+            2 => {
-            .map_err(|_| io::Error::new(io::ErrorKind::InvalidData, "SSTable corruption"))?;
+                // previous format, kept for backward compatibility
-        Ok(Dictionary {
+                let sstable_index_bytes = index_slice.read_bytes()?;
-            sstable_slice,
+                // on the old format, the 1st layer necessarily start immediately, and there is
-            sstable_index,
+                // only a single layer
-            num_terms,
+                let sstable_index =
-            phantom_data: PhantomData,
+                    SSTableIndex::load(sstable_index_bytes, 1, 0).map_err(|_| {
-        })
+                        io::Error::new(io::ErrorKind::InvalidData, "SSTable corruption")
+                    })?;
+                Ok(Dictionary {
+                    sstable_slice,
+                    sstable_index,
+                    num_terms,
+                    phantom_data: PhantomData,
+                })
+            }
+            3 => {
+                let sstable_index_bytes = index_slice.read_bytes()?;
+                let (sstable_index_bytes, mut v3_footer_bytes) = sstable_index_bytes.rsplit(12);
+                let first_layer_offset = v3_footer_bytes.read_u64();
+                let layer_count = v3_footer_bytes.read_u32();
+
+                let sstable_index = SSTableIndex::load(
+                    sstable_index_bytes,
+                    layer_count,
+                    first_layer_offset as usize,
+                )
+                .map_err(|_| io::Error::new(io::ErrorKind::InvalidData, "SSTable corruption"))?;
+                Ok(Dictionary {
+                    sstable_slice,
+                    sstable_index,
+                    num_terms,
+                    phantom_data: PhantomData,
+                })
+            }
+            _ => {
+                return Err(io::Error::new(
+                    io::ErrorKind::Other,
+                    format!(
+                        "Unsuported sstable version, expected {}, found {version}",
+                        crate::SSTABLE_VERSION,
+                    ),
+                ))
+            }
+        }
     }
 
     /// Creates a term dictionary from the supplied bytes.
@@ -227,68 +289,17 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
         self.num_terms as usize
     }
 
-    /// Decode a DeltaReader up to key, returning the number of terms traversed
-    ///
-    /// If the key was not found, returns Ok(None).
-    /// After calling this function, it is possible to call `DeltaReader::value` to get the
-    /// associated value.
-    fn decode_up_to_key<K: AsRef<[u8]>>(
-        &self,
-        key: K,
-        sstable_delta_reader: &mut DeltaReader<TSSTable::ValueReader>,
-    ) -> io::Result<Option<TermOrdinal>> {
-        let mut term_ord = 0;
-        let key_bytes = key.as_ref();
-        let mut ok_bytes = 0;
-        while sstable_delta_reader.advance()? {
-            let prefix_len = sstable_delta_reader.common_prefix_len();
-            let suffix = sstable_delta_reader.suffix();
-
-            match prefix_len.cmp(&ok_bytes) {
-                Ordering::Less => return Ok(None), // popped bytes already matched => too far
-                Ordering::Equal => (),
-                Ordering::Greater => {
-                    // the ok prefix is less than current entry prefix => continue to next elem
-                    term_ord += 1;
-                    continue;
-                }
-            }
-
-            // we have ok_bytes byte of common prefix, check if this key adds more
-            for (key_byte, suffix_byte) in key_bytes[ok_bytes..].iter().zip(suffix) {
-                match suffix_byte.cmp(key_byte) {
-                    Ordering::Less => break,              // byte too small
-                    Ordering::Equal => ok_bytes += 1,     // new matching byte
-                    Ordering::Greater => return Ok(None), // too far
-                }
-            }
-
-            if ok_bytes == key_bytes.len() {
-                if prefix_len + suffix.len() == ok_bytes {
-                    return Ok(Some(term_ord));
-                } else {
-                    // current key is a prefix of current element, not a match
-                    return Ok(None);
-                }
-            }
-
-            term_ord += 1;
-        }
-
-        Ok(None)
-    }
-
     /// Returns the ordinal associated with a given term.
     pub fn term_ord<K: AsRef<[u8]>>(&self, key: K) -> io::Result<Option<TermOrdinal>> {
         let key_bytes = key.as_ref();
 
-        let Some(block_addr) = self.sstable_index.get_block_with_key(key_bytes) else {
+        let Some(block_addr) = self.sstable_index.get_block_with_key(key_bytes)? else {
             return Ok(None);
         };
 
         let first_ordinal = block_addr.first_ordinal;
         let mut sstable_delta_reader = self.sstable_delta_reader_block(block_addr)?;
-        self.decode_up_to_key(key_bytes, &mut sstable_delta_reader)
+        decode_up_to_key(key_bytes, &mut sstable_delta_reader)
             .map(|opt| opt.map(|ord| ord + first_ordinal))
     }
 
@@ -303,7 +314,7 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
     /// the buffer may be modified.
     pub fn ord_to_term(&self, ord: TermOrdinal, bytes: &mut Vec<u8>) -> io::Result<bool> {
         // find block in which the term would be
-        let block_addr = self.sstable_index.get_block_with_ord(ord);
+        let block_addr = self.sstable_index.get_block_with_ord(ord)?;
         let first_ordinal = block_addr.first_ordinal;
 
         // then search inside that block only
@@ -321,7 +332,7 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
     /// Returns the number of terms in the dictionary.
     pub fn term_info_from_ord(&self, term_ord: TermOrdinal) -> io::Result<Option<TSSTable::Value>> {
         // find block in which the term would be
-        let block_addr = self.sstable_index.get_block_with_ord(term_ord);
+        let block_addr = self.sstable_index.get_block_with_ord(term_ord)?;
         let first_ordinal = block_addr.first_ordinal;
 
         // then search inside that block only
@@ -336,7 +347,7 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
 
     /// Lookups the value corresponding to the key.
     pub fn get<K: AsRef<[u8]>>(&self, key: K) -> io::Result<Option<TSSTable::Value>> {
-        if let Some(block_addr) = self.sstable_index.get_block_with_key(key.as_ref()) {
+        if let Some(block_addr) = self.sstable_index.get_block_with_key(key.as_ref())? {
             let sstable_reader = self.sstable_delta_reader_block(block_addr)?;
             return self.do_get(key, sstable_reader);
         }
@@ -345,7 +356,7 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
 
     /// Lookups the value corresponding to the key.
     pub async fn get_async<K: AsRef<[u8]>>(&self, key: K) -> io::Result<Option<TSSTable::Value>> {
-        if let Some(block_addr) = self.sstable_index.get_block_with_key(key.as_ref()) {
+        if let Some(block_addr) = self.sstable_index.get_block_with_key(key.as_ref())? {
             let sstable_reader = self.sstable_delta_reader_block_async(block_addr).await?;
             return self.do_get(key, sstable_reader);
         }
@@ -357,7 +368,7 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
         key: K,
         mut reader: DeltaReader<TSSTable::ValueReader>,
     ) -> io::Result<Option<TSSTable::Value>> {
-        if let Some(_ord) = self.decode_up_to_key(key, &mut reader)? {
+        if let Some(_ord) = decode_up_to_key(key, &mut reader)? {
             Ok(Some(reader.value().clone()))
         } else {
             Ok(None)
@@ -394,6 +405,56 @@ impl<TSSTable: SSTable> Dictionary<TSSTable> {
     }
 }
 
+/// Decode a DeltaReader up to key, returning the number of terms traversed
+///
+/// If the key was not found, returns Ok(None).
+/// After calling this function, it is possible to call `DeltaReader::value` to get the
+/// associated value.
+pub(crate) fn decode_up_to_key<K: AsRef<[u8]>, TValueReader: crate::ValueReader>(
+    key: K,
+    sstable_delta_reader: &mut DeltaReader<TValueReader>,
+) -> io::Result<Option<TermOrdinal>> {
+    let mut term_ord = 0;
+    let key_bytes = key.as_ref();
+    let mut ok_bytes = 0;
+    while sstable_delta_reader.advance()? {
+        let prefix_len = sstable_delta_reader.common_prefix_len();
+        let suffix = sstable_delta_reader.suffix();
+
+        match prefix_len.cmp(&ok_bytes) {
+            Ordering::Less => return Ok(None), // popped bytes already matched => too far
+            Ordering::Equal => (),
+            Ordering::Greater => {
+                // the ok prefix is less than current entry prefix => continue to next elem
+                term_ord += 1;
+                continue;
+            }
+        }
+
+        // we have ok_bytes byte of common prefix, check if this key adds more
+        for (key_byte, suffix_byte) in key_bytes[ok_bytes..].iter().zip(suffix) {
+            match suffix_byte.cmp(key_byte) {
+                Ordering::Less => break,              // byte too small
+                Ordering::Equal => ok_bytes += 1,     // new matching byte
+                Ordering::Greater => return Ok(None), // too far
+            }
+        }
+
+        if ok_bytes == key_bytes.len() {
+            if prefix_len + suffix.len() == ok_bytes {
+                return Ok(Some(term_ord));
+            } else {
+                // current key is a prefix of current element, not a match
+                return Ok(None);
+            }
+        }
+
+        term_ord += 1;
+    }
+
+    Ok(None)
+}
+
 #[cfg(test)]
 mod tests {
     use std::ops::Range;
@@ -459,8 +520,6 @@ mod tests {
 
         let dictionary = Dictionary::<MonotonicU64SSTable>::open(slice).unwrap();
 
-        // if the last block is id 0, tests are meaningless
-        assert_ne!(dictionary.sstable_index.locate_with_ord(u64::MAX), 0);
         assert_eq!(dictionary.num_terms(), 0x3ffff);
         (dictionary, table)
     }
@@ -469,7 +528,7 @@ mod tests {
     fn test_ord_term_conversion() {
         let (dic, slice) = make_test_sstable();
 
-        let block = dic.sstable_index.get_block_with_ord(100_000);
+        let block = dic.sstable_index.get_block_with_ord(100_000).unwrap();
         slice.restrict(block.byte_range);
 
         let mut res = Vec::new();
@@ -495,7 +554,11 @@ mod tests {
 
         // end of a block
         let ordinal = block.first_ordinal - 1;
-        let new_range = dic.sstable_index.get_block_with_ord(ordinal).byte_range;
+        let new_range = dic
+            .sstable_index
+            .get_block_with_ord(ordinal)
+            .unwrap()
+            .byte_range;
         slice.restrict(new_range);
         assert!(dic.ord_to_term(ordinal, &mut res).unwrap());
         assert_eq!(res, format!("{ordinal:05X}").into_bytes());
@@ -505,7 +568,7 @@ mod tests {
 
         // before first block
         // 1st block must be loaded for key-related operations
-        let block = dic.sstable_index.get_block_with_ord(0);
+        let block = dic.sstable_index.get_block_with_ord(0).unwrap();
         slice.restrict(block.byte_range);
 
         assert!(dic.get(b"$$$").unwrap().is_none());
@@ -514,7 +577,11 @@ mod tests {
         // after last block
         // last block must be loaded for ord related operations
         let ordinal = 0x40000 + 10;
-        let new_range = dic.sstable_index.get_block_with_ord(ordinal).byte_range;
+        let new_range = dic
+            .sstable_index
+            .get_block_with_ord(ordinal)
+            .unwrap()
+            .byte_range;
         slice.restrict(new_range);
         assert!(!dic.ord_to_term(ordinal, &mut res).unwrap());
         assert!(dic.term_info_from_ord(ordinal).unwrap().is_none());
@@ -539,11 +606,13 @@ mod tests {
             .sstable_index
             .get_block_with_key(b"10000")
             .unwrap()
+            .unwrap()
             .byte_range;
         let end = dic
             .sstable_index
             .get_block_with_key(b"18000")
             .unwrap()
+            .unwrap()
             .byte_range;
         slice.restrict(start.start..end.end);
 

sstable/src/lib.rs

@@ -1,6 +1,6 @@
 use std::io::{self, Write};
+use std::num::NonZeroU64;
 use std::ops::Range;
-use std::usize;
 
 use merge::ValueMerger;
 
@@ -28,7 +28,13 @@ use crate::value::{RangeValueReader, RangeValueWriter};
 pub type TermOrdinal = u64;
 
 const DEFAULT_KEY_CAPACITY: usize = 50;
-const SSTABLE_VERSION: u32 = 2;
+const SSTABLE_VERSION: u32 = 3;
+
+// TODO tune that value. Maybe it's too little?
+#[cfg(not(test))]
+const DEFAULT_MAX_ROOT_BLOCKS: NonZeroU64 = unsafe { NonZeroU64::new_unchecked(32) };
+#[cfg(test)]
+const DEFAULT_MAX_ROOT_BLOCKS: NonZeroU64 = unsafe { NonZeroU64::new_unchecked(1) };
 
 /// Given two byte string returns the length of
 /// the longest common prefix.
@@ -55,7 +61,7 @@ pub trait SSTable: Sized {
     }
 
     fn writer<W: io::Write>(wrt: W) -> Writer<W, Self::ValueWriter> {
-        Writer::new(wrt)
+        Writer::new(wrt, DEFAULT_MAX_ROOT_BLOCKS)
     }
 
     fn delta_reader(reader: OwnedBytes) -> DeltaReader<Self::ValueReader> {
@@ -178,6 +184,7 @@ where W: io::Write
     delta_writer: DeltaWriter<W, TValueWriter>,
     num_terms: u64,
     first_ordinal_of_the_block: u64,
+    index_max_root_blocks: NonZeroU64,
 }
 
 impl<W, TValueWriter> Writer<W, TValueWriter>
@@ -190,17 +197,18 @@ where
     /// TODO remove this function. (See Issue #1727)
     #[doc(hidden)]
     pub fn create(wrt: W) -> io::Result<Self> {
-        Ok(Self::new(wrt))
+        Ok(Self::new(wrt, DEFAULT_MAX_ROOT_BLOCKS))
     }
 
     /// Creates a new `TermDictionaryBuilder`.
-    pub fn new(wrt: W) -> Self {
+    pub fn new(wrt: W, index_max_root_blocks: NonZeroU64) -> Self {
         Writer {
             previous_key: Vec::with_capacity(DEFAULT_KEY_CAPACITY),
             num_terms: 0u64,
             index_builder: SSTableIndexBuilder::default(),
             delta_writer: DeltaWriter::new(wrt),
             first_ordinal_of_the_block: 0u64,
+            index_max_root_blocks,
         }
     }
 
@@ -302,10 +310,15 @@ where
         // add a final empty block as an end marker
         wrt.write_all(&0u32.to_le_bytes())?;
 
-        let offset = wrt.written_bytes();
+        let index_offset = wrt.written_bytes();
 
-        self.index_builder.serialize(&mut wrt)?;
+        let (layer_count, layer_offset): (u32, u64) = self
-        wrt.write_all(&offset.to_le_bytes())?;
+            .index_builder
+            .serialize(&mut wrt, self.index_max_root_blocks)?;
+        wrt.write_all(&layer_offset.to_le_bytes())?;
+        wrt.write_all(&layer_count.to_le_bytes())?;
+
+        wrt.write_all(&index_offset.to_le_bytes())?;
         wrt.write_all(&self.num_terms.to_le_bytes())?;
 
         SSTABLE_VERSION.serialize(&mut wrt)?;
@@ -389,9 +402,11 @@ mod test {
                 0, // compression
                 1, 0, 12, 0, 32, 17, 20, // index block
                 0, 0, 0, 0, // no more index block
+                0, 0, 0, 0, 0, 0, 0, 0, // first layer offset
+                1, 0, 0, 0, // layer count
                 16, 0, 0, 0, 0, 0, 0, 0, // index start offset
                 3, 0, 0, 0, 0, 0, 0, 0, // num term
-                2, 0, 0, 0, // version
+                3, 0, 0, 0, // version
             ]
         );
         let buffer = OwnedBytes::new(buffer);

sstable/src/sstable_index.rs

@@ -5,77 +5,188 @@ use common::OwnedBytes;
 
 use crate::{common_prefix_len, SSTable, SSTableDataCorruption, TermOrdinal};
 
-#[derive(Default, Debug, Clone)]
+#[derive(Debug, Clone)]
 pub struct SSTableIndex {
-    blocks: Vec<BlockMeta>,
+    root_blocks: Vec<BlockMeta>,
+    layer_count: u32,
+    index_bytes: OwnedBytes,
+}
+
+impl Default for SSTableIndex {
+    fn default() -> Self {
+        SSTableIndex {
+            root_blocks: Vec::new(),
+            layer_count: 1,
+            index_bytes: OwnedBytes::empty(),
+        }
+    }
 }
 
 impl SSTableIndex {
     /// Load an index from its binary representation
-    pub fn load(data: OwnedBytes) -> Result<SSTableIndex, SSTableDataCorruption> {
+    pub fn load(
-        let mut reader = IndexSSTable::reader(data);
+        data: OwnedBytes,
-        let mut blocks = Vec::new();
+        layer_count: u32,
+        first_layer_offset: usize,
+    ) -> Result<SSTableIndex, SSTableDataCorruption> {
+        let (index_bytes, first_layer_slice) = data.split(first_layer_offset);
+        let mut reader = IndexSSTable::reader(first_layer_slice);
+        let mut root_blocks = Vec::new();
 
         while reader.advance().map_err(|_| SSTableDataCorruption)? {
-            blocks.push(BlockMeta {
+            root_blocks.push(BlockMeta {
                 last_key_or_greater: reader.key().to_vec(),
                 block_addr: reader.value().clone(),
             });
         }
 
-        Ok(SSTableIndex { blocks })
+        Ok(SSTableIndex {
-    }
+            root_blocks,
-
+            layer_count,
-    /// Get the [`BlockAddr`] of the requested block.
+            index_bytes,
-    pub(crate) fn get_block(&self, block_id: usize) -> Option<BlockAddr> {
+            // index_bytes: OwnedBytes::empty(),
-        self.blocks
+        })
-            .get(block_id)
-            .map(|block_meta| block_meta.block_addr.clone())
-    }
-
-    /// Get the block id of the block that would contain `key`.
-    ///
-    /// Returns None if `key` is lexicographically after the last key recorded.
-    pub(crate) fn locate_with_key(&self, key: &[u8]) -> Option<usize> {
-        let pos = self
-            .blocks
-            .binary_search_by_key(&key, |block| &block.last_key_or_greater);
-        match pos {
-            Ok(pos) => Some(pos),
-            Err(pos) => {
-                if pos < self.blocks.len() {
-                    Some(pos)
-                } else {
-                    // after end of last block: no block matches
-                    None
-                }
-            }
-        }
     }
 
     /// Get the [`BlockAddr`] of the block that would contain `key`.
     ///
     /// Returns None if `key` is lexicographically after the last key recorded.
-    pub fn get_block_with_key(&self, key: &[u8]) -> Option<BlockAddr> {
+    pub fn get_block_with_key(&self, key: &[u8]) -> io::Result<Option<BlockAddr>> {
-        self.locate_with_key(key).and_then(|id| self.get_block(id))
+        self.iterate_from_key(key).map(|iter| iter.value().cloned())
-    }
-
-    pub(crate) fn locate_with_ord(&self, ord: TermOrdinal) -> usize {
-        let pos = self
-            .blocks
-            .binary_search_by_key(&ord, |block| block.block_addr.first_ordinal);
-
-        match pos {
-            Ok(pos) => pos,
-            // Err(0) can't happen as the sstable starts with ordinal zero
-            Err(pos) => pos - 1,
-        }
     }
 
     /// Get the [`BlockAddr`] of the block containing the `ord`-th term.
-    pub(crate) fn get_block_with_ord(&self, ord: TermOrdinal) -> BlockAddr {
+    pub fn get_block_with_ord(&self, ord: TermOrdinal) -> io::Result<BlockAddr> {
-        // locate_with_ord always returns an index within range
+        let pos = self
-        self.get_block(self.locate_with_ord(ord)).unwrap()
+            .root_blocks
+            .binary_search_by_key(&ord, |block| block.block_addr.first_ordinal);
+
+        let root_pos = match pos {
+            Ok(pos) => pos,
+            // Err(0) can't happen as the sstable starts with ordinal zero
+            Err(pos) => pos - 1,
+        };
+
+        if self.layer_count == 1 {
+            return Ok(self.root_blocks[root_pos].block_addr.clone());
+        }
+
+        let mut next_layer_block_addr = self.root_blocks[root_pos].block_addr.clone();
+        for _ in 1..self.layer_count {
+            let mut sstable_delta_reader = IndexSSTable::delta_reader(
+                self.index_bytes
+                    .slice(next_layer_block_addr.byte_range.clone()),
+            );
+            while sstable_delta_reader.advance()? {
+                if sstable_delta_reader.value().first_ordinal > ord {
+                    break;
+                }
+                next_layer_block_addr = sstable_delta_reader.value().clone();
+            }
+        }
+        Ok(next_layer_block_addr)
+    }
+
+    pub(crate) fn iterate_from_key(&self, key: &[u8]) -> io::Result<ReaderOrSlice<'_>> {
+        let root_pos = self
+            .root_blocks
+            .binary_search_by_key(&key, |block| &block.last_key_or_greater);
+        let root_pos = match root_pos {
+            Ok(pos) => pos,
+            Err(pos) => {
+                if pos < self.root_blocks.len() {
+                    pos
+                } else {
+                    // after end of last block: no block matches
+                    return Ok(ReaderOrSlice::End);
+                }
+            }
+        };
+
+        let mut next_layer_block_addr = self.root_blocks[root_pos].block_addr.clone();
+        let mut last_delta_reader = None;
+        for _ in 1..self.layer_count {
+            // we don't enter this loop for 1 layer index
+            let mut sstable_delta_reader = IndexSSTable::delta_reader(
+                self.index_bytes.slice(next_layer_block_addr.byte_range),
+            );
+            crate::dictionary::decode_up_to_key(key, &mut sstable_delta_reader)?;
+            next_layer_block_addr = sstable_delta_reader.value().clone();
+            last_delta_reader = Some(sstable_delta_reader);
+        }
+
+        if let Some(delta_reader) = last_delta_reader {
+            // reconstruct the current key. We stopped either on the exact key, or just after
+            // either way, common_prefix_len is something that did not change between the
+            // last-key-before-target and the current pos, so those bytes must match the prefix of
+            // `key`. The next bytes can be obtained from the delta reader
+            let mut result_key = Vec::with_capacity(crate::DEFAULT_KEY_CAPACITY);
+            let common_prefix_len = delta_reader.common_prefix_len();
+            let suffix = delta_reader.suffix();
+            let new_len = delta_reader.common_prefix_len() + suffix.len();
+            result_key.resize(new_len, 0u8);
+            result_key[..common_prefix_len].copy_from_slice(&key[..common_prefix_len]);
+            result_key[common_prefix_len..].copy_from_slice(suffix);
+
+            let reader = crate::Reader {
+                key: result_key,
+                delta_reader,
+            };
+            Ok(ReaderOrSlice::Reader(reader))
+        } else {
+            // self.layer_count == 1, there is no lvl2 sstable to decode.
+            Ok(ReaderOrSlice::Iter(&self.root_blocks, root_pos))
+        }
+    }
+}
+
+pub(crate) enum ReaderOrSlice<'a> {
+    Reader(crate::Reader<crate::value::index::IndexValueReader>),
+    Iter(&'a [BlockMeta], usize),
+    End,
+}
+
+impl<'a> ReaderOrSlice<'a> {
+    pub fn advance(&mut self) -> Result<bool, SSTableDataCorruption> {
+        match self {
+            ReaderOrSlice::Reader(reader) => {
+                let res = reader.advance().map_err(|_| SSTableDataCorruption);
+                if !matches!(res, Ok(true)) {
+                    *self = ReaderOrSlice::End;
+                }
+                res
+            }
+            ReaderOrSlice::Iter(slice, index) => {
+                *index += 1;
+                if *index < slice.len() {
+                    Ok(true)
+                } else {
+                    *self = ReaderOrSlice::End;
+                    Ok(false)
+                }
+            }
+            ReaderOrSlice::End => Ok(false),
+        }
+    }
+
+    /// Get current key. Always Some(_) unless last call to advance returned something else than
+    /// Ok(true)
+    pub fn key(&self) -> Option<&[u8]> {
+        match self {
+            ReaderOrSlice::Reader(reader) => Some(reader.key()),
+            ReaderOrSlice::Iter(slice, index) => Some(&slice[*index].last_key_or_greater),
+            ReaderOrSlice::End => None,
+        }
+    }
+
+    /// Get current value. Always Some(_) unless last call to advance returned something else than
+    /// Ok(true)
+    pub fn value(&self) -> Option<&BlockAddr> {
+        match self {
+            ReaderOrSlice::Reader(reader) => Some(reader.value()),
+            ReaderOrSlice::Iter(slice, index) => Some(&slice[*index].block_addr),
+            ReaderOrSlice::End => None,
+        }
     }
 }
 
@@ -124,13 +235,13 @@ impl SSTableIndexBuilder {
     /// try to find a shorter alternative to the last key of the last block
     /// that is still smaller than the next key.
     pub(crate) fn shorten_last_block_key_given_next_key(&mut self, next_key: &[u8]) {
-        if let Some(last_block) = self.index.blocks.last_mut() {
+        if let Some(last_block) = self.index.root_blocks.last_mut() {
             find_shorter_str_in_between(&mut last_block.last_key_or_greater, next_key);
         }
     }
 
     pub fn add_block(&mut self, last_key: &[u8], byte_range: Range<usize>, first_ordinal: u64) {
-        self.index.blocks.push(BlockMeta {
+        self.index.root_blocks.push(BlockMeta {
             last_key_or_greater: last_key.to_vec(),
             block_addr: BlockAddr {
                 byte_range,
@@ -139,31 +250,90 @@ impl SSTableIndexBuilder {
         })
     }
 
-    pub fn serialize<W: std::io::Write>(&self, wrt: W) -> io::Result<()> {
+    pub fn serialize<W: std::io::Write>(
-        // we can't use a plain writer as it would generate an index
+        &self,
-        let mut sstable_writer = IndexSSTable::delta_writer(wrt);
+        wrt: W,
+        index_max_root_blocks: std::num::NonZeroU64,
+    ) -> io::Result<(u32, u64)> {
+        let index_max_root_blocks = index_max_root_blocks.get();
 
-        // in tests, set a smaller block size to stress-test
+        let mut wrt = common::CountingWriter::wrap(wrt);
-        #[cfg(test)]
+        let mut next_layer = write_sstable_layer(&mut wrt, &self.index.root_blocks, 0)?;
-        sstable_writer.set_block_len(16);
 
-        let mut previous_key = Vec::with_capacity(crate::DEFAULT_KEY_CAPACITY);
+        let mut layer_count = 1;
-        for block in self.index.blocks.iter() {
+        let mut offset = 0;
-            let keep_len = common_prefix_len(&previous_key, &block.last_key_or_greater);
+        while next_layer.len() as u64 > index_max_root_blocks {
+            offset = wrt.written_bytes();
+            layer_count += 1;
 
-            sstable_writer.write_suffix(keep_len, &block.last_key_or_greater[keep_len..]);
+            next_layer = write_sstable_layer(&mut wrt, &next_layer, offset as usize)?;
-            sstable_writer.write_value(&block.block_addr);
-            sstable_writer.flush_block_if_required()?;
-
-            previous_key.clear();
-            previous_key.extend_from_slice(&block.last_key_or_greater);
         }
-        sstable_writer.flush_block()?;
+        Ok((layer_count, offset))
-        sstable_writer.finish().write_all(&0u32.to_le_bytes())?;
-        Ok(())
     }
 }
 
+fn write_sstable_layer<W: std::io::Write>(
+    wrt: W,
+    layer_content: &[BlockMeta],
+    offset: usize,
+) -> io::Result<Vec<BlockMeta>> {
+    // we can't use a plain writer as it would generate an index
+    // also disable compression, the index is small anyway, and it's the most costly part of
+    // opening that kind of sstable
+    let mut sstable_writer =
+        crate::DeltaWriter::<_, crate::value::index::IndexValueWriter>::new_no_compression(wrt);
+
+    // in tests, set a smaller block size to stress-test
+    #[cfg(test)]
+    sstable_writer.set_block_len(16);
+
+    let mut next_layer = Vec::new();
+    let mut previous_key = Vec::with_capacity(crate::DEFAULT_KEY_CAPACITY);
+    let mut first_ordinal = None;
+    for block in layer_content.iter() {
+        if first_ordinal.is_none() {
+            first_ordinal = Some(block.block_addr.first_ordinal);
+        }
+        let keep_len = common_prefix_len(&previous_key, &block.last_key_or_greater);
+
+        sstable_writer.write_suffix(keep_len, &block.last_key_or_greater[keep_len..]);
+        sstable_writer.write_value(&block.block_addr);
+        if let Some(range) = sstable_writer.flush_block_if_required()? {
+            let real_range = (range.start + offset)..(range.end + offset);
+            let block_meta = BlockMeta {
+                last_key_or_greater: block.last_key_or_greater.clone(),
+                block_addr: BlockAddr {
+                    byte_range: real_range,
+                    first_ordinal: first_ordinal.take().unwrap(),
+                },
+            };
+            next_layer.push(block_meta);
+            previous_key.clear();
+        } else {
+            previous_key.extend_from_slice(&block.last_key_or_greater);
+            previous_key.resize(block.last_key_or_greater.len(), 0u8);
+            previous_key[keep_len..].copy_from_slice(&block.last_key_or_greater[keep_len..]);
+        }
+    }
+    if let Some(range) = sstable_writer.flush_block()? {
+        if let Some(last_block) = layer_content.last() {
+            // not going here means an empty table (?!)
+            let real_range = (range.start + offset)..(range.end + offset);
+            let block_meta = BlockMeta {
+                last_key_or_greater: last_block.last_key_or_greater.clone(),
+                block_addr: BlockAddr {
+                    byte_range: real_range,
+                    first_ordinal: first_ordinal.take().unwrap(),
+                },
+            };
+            next_layer.push(block_meta);
+        }
+    }
+    sstable_writer.finish().write_all(&0u32.to_le_bytes())?;
+
+    Ok(next_layer)
+}
+
 /// SSTable representing an index
 ///
 /// `last_key_or_greater` is used as the key, the value contains the
@@ -194,28 +364,77 @@ mod tests {
         sstable_builder.add_block(b"ccc", 30..40, 10u64);
         sstable_builder.add_block(b"dddd", 40..50, 15u64);
         let mut buffer: Vec<u8> = Vec::new();
-        sstable_builder.serialize(&mut buffer).unwrap();
+        sstable_builder
+            .serialize(&mut buffer, crate::DEFAULT_MAX_ROOT_BLOCKS)
+            .unwrap();
         let buffer = OwnedBytes::new(buffer);
-        let sstable_index = SSTableIndex::load(buffer).unwrap();
+        let sstable_index = SSTableIndex::load(buffer, 1, 0).unwrap();
         assert_eq!(
-            sstable_index.get_block_with_key(b"bbbde"),
+            sstable_index.get_block_with_key(b"bbbde").unwrap(),
             Some(BlockAddr {
                 first_ordinal: 10u64,
                 byte_range: 30..40
             })
         );
 
-        assert_eq!(sstable_index.locate_with_key(b"aa").unwrap(), 0);
+        assert_eq!(
-        assert_eq!(sstable_index.locate_with_key(b"aaa").unwrap(), 0);
+            sstable_index
-        assert_eq!(sstable_index.locate_with_key(b"aab").unwrap(), 1);
+                .get_block_with_key(b"aa")
-        assert_eq!(sstable_index.locate_with_key(b"ccc").unwrap(), 2);
+                .unwrap()
-        assert!(sstable_index.locate_with_key(b"e").is_none());
+                .unwrap()
+                .first_ordinal,
+            0
+        );
+        assert_eq!(
+            sstable_index
+                .get_block_with_key(b"aaa")
+                .unwrap()
+                .unwrap()
+                .first_ordinal,
+            0
+        );
+        assert_eq!(
+            sstable_index
+                .get_block_with_key(b"aab")
+                .unwrap()
+                .unwrap()
+                .first_ordinal,
+            5
+        );
+        assert_eq!(
+            sstable_index
+                .get_block_with_key(b"ccc")
+                .unwrap()
+                .unwrap()
+                .first_ordinal,
+            10
+        );
+        assert!(sstable_index.get_block_with_key(b"e").unwrap().is_none());
 
-        assert_eq!(sstable_index.locate_with_ord(0), 0);
+        assert_eq!(
-        assert_eq!(sstable_index.locate_with_ord(1), 0);
+            sstable_index.get_block_with_ord(0).unwrap().first_ordinal,
-        assert_eq!(sstable_index.locate_with_ord(4), 0);
+            0
-        assert_eq!(sstable_index.locate_with_ord(5), 1);
+        );
-        assert_eq!(sstable_index.locate_with_ord(100), 3);
+        assert_eq!(
+            sstable_index.get_block_with_ord(1).unwrap().first_ordinal,
+            0
+        );
+        assert_eq!(
+            sstable_index.get_block_with_ord(4).unwrap().first_ordinal,
+            0
+        );
+        assert_eq!(
+            sstable_index.get_block_with_ord(5).unwrap().first_ordinal,
+            5
+        );
+        assert_eq!(
+            sstable_index.get_block_with_ord(6).unwrap().first_ordinal,
+            5
+        );
+        assert_eq!(
+            sstable_index.get_block_with_ord(100).unwrap().first_ordinal,
+            15
+        );
     }
 
     #[test]
@@ -226,10 +445,12 @@ mod tests {
         sstable_builder.add_block(b"ccc", 30..40, 10u64);
         sstable_builder.add_block(b"dddd", 40..50, 15u64);
         let mut buffer: Vec<u8> = Vec::new();
-        sstable_builder.serialize(&mut buffer).unwrap();
+        sstable_builder
+            .serialize(&mut buffer, crate::DEFAULT_MAX_ROOT_BLOCKS)
+            .unwrap();
         buffer[2] = 9u8;
         let buffer = OwnedBytes::new(buffer);
-        let data_corruption_err = SSTableIndex::load(buffer).err().unwrap();
+        let data_corruption_err = SSTableIndex::load(buffer, 1, 0).err().unwrap();
         assert!(matches!(data_corruption_err, SSTableDataCorruption));
     }
 

sstable/src/streamer.rs

@@ -110,7 +110,7 @@ where
             Bound::Included(key) | Bound::Excluded(key) => self
                 .term_dict
                 .sstable_index
-                .get_block_with_key(key)
+                .get_block_with_key(key)?
                 .map(|block| block.first_ordinal)
                 .unwrap_or(0),
             Bound::Unbounded => 0,

sstable/src/value/index.rs

@@ -3,6 +3,10 @@ use std::io;
 use crate::value::{deserialize_vint_u64, ValueReader, ValueWriter};
 use crate::{vint, BlockAddr};
 
+// TODO define a LazyIndexValueReader?
+// one which keeps state could be useful for ord_to_block fns,
+// one which doesn't at all woud be perfect for term_to_block fns
+// pending bench to asses real impact
 #[derive(Default)]
 pub(crate) struct IndexValueReader {
     vals: Vec<BlockAddr>,