diff --git a/src/indexer/merger.rs b/src/indexer/merger.rs
index b9b8b5635..55e0e0b88 100644
--- a/src/indexer/merger.rs
+++ b/src/indexer/merger.rs
@@ -335,12 +335,16 @@ impl IndexMerger {
     fn write_storable_fields(&self, store_writer: &mut StoreWriter) -> Result<()> {
         for reader in &self.readers {
             let store_reader = reader.get_store_reader();
-            for doc_id in 0..reader.max_doc() {
-                if !reader.is_deleted(doc_id) {
-                    let doc = store_reader.get(doc_id)?;
-                    let field_values: Vec<&FieldValue> = doc.field_values().iter().collect();
-                    store_writer.store(&field_values)?;
+            if reader.num_deleted_docs() > 0 {
+                for doc_id in 0..reader.max_doc() {
+                    if !reader.is_deleted(doc_id) {
+                        let doc = store_reader.get(doc_id)?;
+                        let field_values: Vec<&FieldValue> = doc.field_values().iter().collect();
+                        store_writer.store(&field_values)?;
+                    }
                 }
+            } else {
+                store_writer.stack(store_reader)?;
             }
         }
         Ok(())
diff --git a/src/store/reader.rs b/src/store/reader.rs
index 14c9b5d25..c96324149 100644
--- a/src/store/reader.rs
+++ b/src/store/reader.rs
@@ -34,22 +34,33 @@ impl StoreReader {
         }
     }
 
-    fn block_offset(&self, doc_id: DocId) -> (DocId, u64) {
+    pub fn block_index(&self) -> SkipList<u64> {
         SkipList::from(self.offset_index_source.as_slice())
+    }
+
+    fn block_offset(&self, doc_id: DocId) -> (DocId, u64) {
+        self.block_index()
             .seek(doc_id + 1)
             .unwrap_or((0u32, 0u64))
     }
 
+    pub fn block_data(&self) -> &[u8] {
+        self.data.as_slice()
+    }
+
+    pub fn compressed_block(&self, addr: usize) -> &[u8] {
+        let total_buffer = self.data.as_slice();
+        let mut buffer = &total_buffer[addr..];
+        let block_len = u32::deserialize(&mut buffer).expect("") as usize;
+        &buffer[..block_len]
+    }
+
     fn read_block(&self, block_offset: usize) -> io::Result<()> {
         if block_offset != *self.current_block_offset.borrow() {
             let mut current_block_mut = self.current_block.borrow_mut();
             current_block_mut.clear();
-            let total_buffer = self.data.as_slice();
-            let mut cursor = &total_buffer[block_offset..];
-            let block_length = u32::deserialize(&mut cursor).unwrap();
-            let block_array: &[u8] = &total_buffer
-                [(block_offset + 4 as usize)..(block_offset + 4 + block_length as usize)];
-            let mut lz4_decoder = lz4::Decoder::new(block_array)?;
+            let compressed_block = self.compressed_block(block_offset);
+            let mut lz4_decoder = lz4::Decoder::new(compressed_block)?;
             *self.current_block_offset.borrow_mut() = usize::max_value();
             lz4_decoder.read_to_end(&mut current_block_mut).map(|_| ())?;
             *self.current_block_offset.borrow_mut() = block_offset;
diff --git a/src/store/writer.rs b/src/store/writer.rs
index 6dacfd6a1..7d0482272 100644
--- a/src/store/writer.rs
+++ b/src/store/writer.rs
@@ -3,6 +3,7 @@ use DocId;
 use schema::FieldValue;
 use common::BinarySerializable;
 use std::io::{self, Write};
+use super::StoreReader;
 use lz4;
 use datastruct::SkipListBuilder;
 use common::CountingWriter;
@@ -60,6 +61,35 @@ impl StoreWriter {
         Ok(())
     }
 
+    /// Stacks a store reader on top of the documents written so far.
+    /// This method is an optimization compared to iterating over the documents
+    /// in the store and adding them one by one, as the store's data will
+    /// not be decompressed and then recompressed.
+    pub fn stack(&mut self, store_reader: &StoreReader) -> io::Result<()> {
+        if !self.current_block.is_empty() {
+            self.write_and_compress_block()?;
+            self.offset_index_writer.insert(
+                self.doc,
+                &(self.writer.written_bytes() as u64),
+            )?;
+        }
+        let doc_offset = self.doc;
+        let start_offset = self.writer.written_bytes() as u64;
+
+        // just bulk write all of the block of the given reader.
+        self.writer.write_all(store_reader.block_data())?;
+
+        // concatenate the index of the `store_reader`, after translating
+        // its start doc id and its start file offset.
+        for (next_doc_id, block_addr) in store_reader.block_index() {
+            self.doc = doc_offset + next_doc_id;
+            self.offset_index_writer.insert(
+                self.doc,
+                &(start_offset + block_addr))?;
+        }
+        Ok(())
+    }
+
     fn write_and_compress_block(&mut self) -> io::Result<()> {
         self.intermediary_buffer.clear();
         {
diff --git a/src/termdict/streamdict/delta_encoder.rs b/src/termdict/streamdict/delta_encoder.rs
index b3d73e3b8..cf47105f5 100644
--- a/src/termdict/streamdict/delta_encoder.rs
+++ b/src/termdict/streamdict/delta_encoder.rs
@@ -49,19 +49,26 @@ impl TermDeltaDecoder {
         }
     }
 
+
+    // code
+    // first bit represents whether the prefix / suffix len can be encoded
+    // on the same byte. (the next one)
+    //
+
     #[inline(always)]
     pub fn decode<'a>(&mut self, code: u8, mut cursor: &'a [u8]) -> &'a [u8] {
-        let (prefix_len, suffix_len): (usize, usize) = if (code & 1u8) == 1u8 {
-            let b = cursor[0];
-            cursor = &cursor[1..];
-            let prefix_len = (b & 15u8) as usize;
-            let suffix_len = (b >> 4u8) as usize;
-            (prefix_len, suffix_len)
-        } else {
-            let prefix_len = u32::deserialize(&mut cursor).unwrap();
-            let suffix_len = u32::deserialize(&mut cursor).unwrap();
-            (prefix_len as usize, suffix_len as usize)
-        };
+        let (prefix_len, suffix_len): (usize, usize) =
+            if (code & 1u8) == 1u8 {
+                let b = cursor[0];
+                cursor = &cursor[1..];
+                let prefix_len = (b & 15u8) as usize;
+                let suffix_len = (b >> 4u8) as usize;
+                (prefix_len, suffix_len)
+            } else {
+                let prefix_len = u32::deserialize(&mut cursor).unwrap();
+                let suffix_len = u32::deserialize(&mut cursor).unwrap();
+                (prefix_len as usize, suffix_len as usize)
+            };
         unsafe { self.term.set_len(prefix_len) };
         self.term.extend_from_slice(&(*cursor)[..suffix_len]);
         &cursor[suffix_len..]
@@ -75,8 +82,8 @@ impl TermDeltaDecoder {
 #[derive(Default)]
 pub struct DeltaTermInfo {
     pub doc_freq: u32,
-    pub delta_postings_offset: u32,
-    pub delta_positions_offset: u32,
+    pub delta_postings_offset: u64,
+    pub delta_positions_offset: u64,
     pub positions_inner_offset: u8,
 }
 
@@ -101,7 +108,7 @@ impl TermInfoDeltaEncoder {
         let mut delta_term_info = DeltaTermInfo {
             doc_freq: term_info.doc_freq,
             delta_postings_offset: term_info.postings_offset - self.term_info.postings_offset,
-            delta_positions_offset: 0,
+            delta_positions_offset: 0u64,
             positions_inner_offset: 0,
         };
         if self.has_positions {
@@ -152,7 +159,7 @@ impl TermInfoDeltaDecoder {
         let mut v: u64 = unsafe { *(cursor.as_ptr() as *const u64) };
         let doc_freq: u32 = (v as u32) & make_mask(num_bytes_docfreq);
         v >>= (num_bytes_docfreq as u64) * 8u64;
-        let delta_postings_offset: u32 = (v as u32) & make_mask(num_bytes_postings_offset);
+        let delta_postings_offset: u64 = v & make_mask(num_bytes_postings_offset);
         cursor = &cursor[num_bytes_docfreq + num_bytes_postings_offset..];
         self.term_info.doc_freq = doc_freq;
         self.term_info.postings_offset += delta_postings_offset;
diff --git a/src/tokenizer/tokenizer.rs b/src/tokenizer/tokenizer.rs
index 50fc42a39..8526e812b 100644
--- a/src/tokenizer/tokenizer.rs
+++ b/src/tokenizer/tokenizer.rs
@@ -195,6 +195,10 @@ pub trait TokenStream {
     /// Returns a mutable reference to the current token.
     fn token_mut(&mut self) -> &mut Token;
 
+    /// Helper to iterate over tokens. It
+    /// simply combines a call to `.advance()`
+    /// and `.token()`.
+    ///
     /// ```
     /// # extern crate tantivy;
     /// # use tantivy::tokenizer::*;