diff --git a/src/main.rs b/src/main.rs
index 5e16881..e996ef2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -20,7 +20,7 @@ use byteorder::{LittleEndian, WriteBytesExt};
 use crypto::digest::Digest;
 use crypto::sha2::Sha256;
 use itertools::enumerate;
-use rocksdb::{DBCompactionStyle, DBCompressionType, WriteBatch, DB};
+use rocksdb::{DBCompactionStyle, DBCompressionType, WriteBatch, WriteOptions, DB};
 // use serde_json::Value;
 use std::collections::{HashMap, VecDeque};
 use std::fmt::Write;
@@ -31,14 +31,24 @@ const HEADER_SIZE: usize = 80;
 const HASH_LEN: usize = 8;
 
 type HeaderMap = HashMap<String, BlockHeader>;
+type Bytes = Vec<u8>;
+
+fn be_hex(data: &[u8]) -> String {
+    let mut ret = String::with_capacity(data.len() * 2);
+    for item in data.iter().rev() {
+        ret.push(std::char::from_digit((*item / 0x10) as u32, 16).unwrap());
+        ret.push(std::char::from_digit((*item & 0x0f) as u32, 16).unwrap());
+    }
+    ret
+}
 
 fn get(resource: &str) -> reqwest::Response {
     let url = format!("http://localhost:8332/rest/{}", resource);
     reqwest::get(&url).unwrap()
 }
 
-fn get_bin(resource: &str) -> Vec<u8> {
-    let mut buf: Vec<u8> = vec![];
+fn get_bin(resource: &str) -> Bytes {
+    let mut buf = Bytes::new();
     let mut resp = get(resource);
     resp.copy_to(&mut buf).unwrap();
     buf
@@ -48,7 +58,6 @@ fn get_headers() -> (HeaderMap, String) {
     let mut headers = HashMap::new();
     let mut blockhash =
         String::from("000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"); // genesis
-    info!("loading headers from {}", blockhash);
     loop {
         let data = get_bin(&format!("headers/2000/{}.bin", blockhash));
         let num_of_headers = data.len() / HEADER_SIZE;
@@ -79,8 +88,8 @@ fn enumerate_headers(headers: &HeaderMap, bestblockhash: &str) -> Vec<(usize, St
 }
 
 struct Row {
-    key: Vec<u8>,
-    value: Vec<u8>,
+    key: Bytes,
+    value: Bytes,
 }
 
 fn index_block(block: &Block, height: usize) -> Vec<Row> {
@@ -200,24 +209,28 @@ struct Store {
     start: PreciseTime,
 }
 
+struct StoreOptions {
+    auto_compact: bool,
+}
+
 impl Store {
     /// Opens a new RocksDB at the specified location.
-    pub fn open(path: &str) -> Store {
-        let mut opts = rocksdb::Options::default();
-        opts.create_if_missing(true);
-        opts.set_compaction_style(DBCompactionStyle::Level);
-        opts.set_max_open_files(256);
-        opts.set_use_fsync(false);
-        opts.set_compression_type(DBCompressionType::None);
-        opts.set_target_file_size_base(64 << 20);
-        opts.set_write_buffer_size(256 << 20);
+    pub fn open(path: &str, opts: StoreOptions) -> Store {
+        let mut db_opts = rocksdb::Options::default();
+        db_opts.create_if_missing(true);
+        db_opts.set_compaction_style(DBCompactionStyle::Level);
+        db_opts.set_max_open_files(256);
+        db_opts.set_use_fsync(false);
+        db_opts.set_compression_type(DBCompressionType::None);
+        db_opts.set_target_file_size_base(64 << 20);
+        db_opts.set_write_buffer_size(256 << 20);
+        db_opts.set_disable_auto_compactions(!opts.auto_compact);
 
         let mut block_opts = rocksdb::BlockBasedOptions::default();
         block_opts.set_block_size(256 << 10);
-
-        // opts.set_disable_auto_compactions(true); // for initial sync?
+        info!("opening {}", path);
         Store {
-            db: DB::open(&opts, &path).unwrap(),
+            db: DB::open(&db_opts, &path).unwrap(),
             rows: vec![],
             start: PreciseTime::now(),
         }
@@ -229,21 +242,63 @@ impl Store {
         if elapsed < Duration::seconds(60) && self.rows.len() < 10_000_000 {
             return;
         }
+        self.flush();
+    }
+
+    pub fn flush(&mut self) {
         let mut batch = WriteBatch::default();
         for row in &self.rows {
             batch.put(row.key.as_slice(), row.value.as_slice()).unwrap();
         }
-        self.db.write(batch).unwrap();
+        let mut opts = WriteOptions::new();
+        opts.set_sync(true);
+        self.db.write_opt(batch, &opts).unwrap();
         self.rows.clear();
         self.start = PreciseTime::now();
     }
+
+    pub fn read_headers(&mut self) -> HashMap<String, BlockHeader> {
+        let mut headers = HashMap::new();
+        for row in self.scan(b"B") {
+            let blockhash = be_hex(&row.key);
+            let header: BlockHeader = deserialize(&row.value).unwrap();
+            headers.insert(blockhash, header);
+        }
+        headers
+    }
+
+    // Use generators ???
+    fn scan(&mut self, prefix: &[u8]) -> Vec<Row> {
+        let mut rows = Vec::new();
+        let mut iter = self.db.raw_iterator();
+        let prefix_len = prefix.len();
+        iter.seek(prefix);
+        while iter.valid() {
+            let key = &iter.key().unwrap();
+            if &key[..prefix_len] != prefix {
+                break;
+            }
+            rows.push(Row {
+                key: key[prefix_len..].to_vec(),
+                value: iter.value().unwrap().to_vec(),
+            });
+            iter.next();
+        }
+        rows
+    }
 }
 
 fn main() {
     simple_logger::init_with_level(log::Level::Info).unwrap();
+    let mut store = Store::open("db/mainnet", StoreOptions { auto_compact: true });
+
+    let indexed_headers = store.read_headers();
+    info!("indexed {} headers", indexed_headers.len());
+
     let (headers, blockhash) = get_headers();
-    let hashes = enumerate_headers(&headers, &blockhash);
-    info!("loading {} blocks", hashes.len());
+    let mut hashes: Vec<(usize, String)> = enumerate_headers(&headers, &blockhash);
+    hashes.retain(|item| !indexed_headers.contains_key(&item.1));
+    info!("indexing {} blocks", hashes.len());
 
     let mut timer = Timer::new();
 
@@ -251,14 +306,12 @@ fn main() {
     let mut rows_size = 0usize;
     let mut num_of_rows = 0usize;
 
-    let mut store = Store::open("db/mainnet");
-
     for &(height, ref blockhash) in &hashes {
         timer.start("get");
         let buf = get_bin(&format!("block/{}.bin", &blockhash));
 
         timer.start("parse");
-        let block: Block = deserialize(buf.as_slice()).unwrap();
+        let block: Block = deserialize(&buf).unwrap();
 
         timer.start("index");
         let rows = index_block(&block, height);
@@ -285,4 +338,5 @@ fn main() {
             );
         }
     }
+    store.flush();
 }