diff --git a/Cargo.toml b/Cargo.toml
index 6411054f7..ce2fe204b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,3 +9,4 @@ itertools = "0.4.5"
 memmap = "0.2.3"
 lazy_static = "0.1.*"
 regex = "0.1"
+fst = "0.1.26"
diff --git a/src/core/directory.rs b/src/core/directory.rs
index 3caa90fa1..14f2e9733 100644
--- a/src/core/directory.rs
+++ b/src/core/directory.rs
@@ -81,8 +81,7 @@ impl Segment {
 //  MemoryPointer
 
 pub trait MemoryPointer {
-    fn len(&self) -> usize;
-    fn ptr(&self) -> *const u8;
+    fn data(&self) -> &[u8];
 }
 
 /////////////////////////////////////////////////////////
@@ -94,31 +93,25 @@ pub struct ResidentMemoryPointer {
 }
 
 impl MemoryPointer for ResidentMemoryPointer {
-    fn len(&self) -> usize {
-        self.len
-    }
-    fn ptr(&self) -> *const u8 {
-        &self.data[0]
+    fn data(&self) -> &[u8] {
+        self.data.deref()
     }
 }
 
 
 
 /////////////////////////////////////////////////////////
+// MmapMemory
 //
-//
-
 
 pub struct MmapMemory(Mmap);
 
 impl MemoryPointer for MmapMemory {
-    fn len(&self) -> usize {
+    fn data(&self) -> &[u8] {
         let &MmapMemory(ref mmap) = self;
-        mmap.len()
-    }
-    fn ptr(&self) -> *const u8 {
-        let &MmapMemory(ref mmap) = self;
-        mmap.ptr()
+        unsafe {
+            mmap.as_slice()
+        }
     }
 }
 
diff --git a/src/core/global.rs b/src/core/global.rs
index c3f986d63..ca66384e5 100644
--- a/src/core/global.rs
+++ b/src/core/global.rs
@@ -1,6 +1,13 @@
+use std::io::{BufWriter, Write};
+use std::io;
 
 pub type DocId = usize;
 
 // pub trait SeekableIterator<T>: Iterator<T> {
 //     pub fn seek(&mut self, el: &T) -> bool;
 // }
+
+
+pub trait Flushable {
+    fn flush<W: Write>(&self, writer: &mut W) -> Result<usize, io::Error>;
+}
diff --git a/src/core/postings.rs b/src/core/postings.rs
index b97a90064..72cb134cd 100644
--- a/src/core/postings.rs
+++ b/src/core/postings.rs
@@ -7,6 +7,18 @@ use core::global::DocId;
 // use std::slice;
 use std::vec;
 
+
+/////////////////////////////
+
+
+pub trait PostingsWriter {
+	fn suscribe(&mut self, DocId);
+}
+
+
+////////////////////////////////////
+
+
 pub trait Postings {
 	type IteratorType: Iterator<Item=DocId>;
 	fn iter(&self) -> Self::IteratorType;
diff --git a/src/core/writer.rs b/src/core/writer.rs
index a5e4ddca7..b711d9ea0 100644
--- a/src/core/writer.rs
+++ b/src/core/writer.rs
@@ -6,27 +6,57 @@ use core::directory::Directory;
 use core::analyzer::tokenize;
 use std::collections::{HashMap, BTreeMap};
 use core::DocId;
+use core::postings::PostingsWriter;
+use core::global::Flushable;
+use std::io::{BufWriter, Write};
+use std::mem;
+use byteorder::{NativeEndian, ReadBytesExt, WriteBytesExt};
 
-pub struct PostingsWriter {
+
+pub struct SimplePostingsWriter {
 	doc_ids: Vec<DocId>,
 }
 
-impl PostingsWriter {
-    pub fn new()->PostingsWriter {
-        PostingsWriter {
+impl SimplePostingsWriter {
+    pub fn new() -> SimplePostingsWriter {
+        SimplePostingsWriter {
             doc_ids: Vec::new(),
         }
     }
+}
 
-	pub fn suscribe(&mut self, doc_id: DocId) {
+impl PostingsWriter for SimplePostingsWriter {
+	fn suscribe(&mut self, doc_id: DocId) {
 		self.doc_ids.push(doc_id);
 	}
 }
 
+impl Flushable for SimplePostingsWriter {
+	fn flush<W: Write>(&self, writer: &mut W) -> Result<usize, io::Error> {
+		let num_docs = self.doc_ids.len() as u64;
+		writer.write_u64::<NativeEndian>(num_docs);
+		for &doc_id in self.doc_ids.iter() {
+			writer.write_u64::<NativeEndian>(doc_id as u64);
+		}
+		Ok(1)
+	}
+}
+
 struct FieldWriter {
-    postings: Vec<PostingsWriter>,
+    postings: Vec<SimplePostingsWriter>,
     term_index: BTreeMap<String, usize>,
 }
+//
+// impl Flushable for FieldWriter {
+// 	fn flush<W: Write>(&self, writer: &mut W) -> Result<usize, io::Error> {
+// 		let num_docs = self.doc_ids.len() as u64;
+// 		writer.write_u64::<NativeEndian>(num_docs);
+// 		for &doc_id in self.doc_ids.iter() {
+// 			writer.write_u64::<NativeEndian>(doc_id as u64);
+// 		}
+// 		Ok(1)
+// 	}
+// }
 
 impl FieldWriter {
     pub fn new() -> FieldWriter {
@@ -36,7 +66,7 @@ impl FieldWriter {
         }
     }
 
-    pub fn get_postings_writer(&mut self, term_text: &str) -> &mut PostingsWriter {
+    pub fn get_postings_writer(&mut self, term_text: &str) -> &mut SimplePostingsWriter {
         match self.term_index.get(term_text) {
             Some(unord_id) => {
                 return &mut self.postings[*unord_id];
@@ -44,7 +74,7 @@ impl FieldWriter {
             None => {}
         }
         let unord_id = self.term_index.len();
-        self.postings.push(PostingsWriter::new());
+        self.postings.push(SimplePostingsWriter::new());
         self.term_index.insert(String::from(term_text), unord_id.clone());
         &mut self.postings[unord_id]
     }
diff --git a/src/lib.rs b/src/lib.rs
index d6f4668ce..3f535347f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,4 +1,5 @@
 #[macro_use]
 extern crate lazy_static;
+extern crate byteorder;
 
 pub mod core;
diff --git a/tests/core.rs b/tests/core.rs
index 6e16a0ace..2f422a483 100644
--- a/tests/core.rs
+++ b/tests/core.rs
@@ -1,5 +1,6 @@
 extern crate tantivy;
 extern crate itertools;
+extern crate byteorder;
 
 use tantivy::core::DocId;
 use tantivy::core::postings::{VecPostings, intersection};
@@ -9,6 +10,11 @@ use tantivy::core::writer::IndexWriter;
 use tantivy::core::directory::Directory;
 use tantivy::core::schema::{Field, Document};
 use tantivy::core::reader::IndexReader;
+use tantivy::core::writer::SimplePostingsWriter;
+use tantivy::core::postings::PostingsWriter;
+use tantivy::core::global::Flushable;
+use std::io::{ BufWriter, Write };
+use std::convert::From;
 
 #[test]
 fn test_intersection() {
@@ -39,3 +45,16 @@ fn test_indexing() {
         let index_reader = IndexReader::open(&directory);
     }
 }
+
+#[test]
+fn test_postings_writer() {
+    let mut postings_writer = SimplePostingsWriter::new();
+    postings_writer.suscribe(1);
+    postings_writer.suscribe(4);
+    postings_writer.suscribe(5);
+    postings_writer.suscribe(17);
+    let mut buffer: Vec<u8> = Vec::new();
+    assert_eq!(buffer.len(), 0);
+    postings_writer.flush(&mut buffer);
+    assert_eq!(buffer.len(), 5 * 8);
+}