diff --git a/sync/src/block/downloader/body.rs b/sync/src/block/downloader/body.rs
index cc46e4d418..ff1390da22 100644
--- a/sync/src/block/downloader/body.rs
+++ b/sync/src/block/downloader/body.rs
@@ -16,20 +16,31 @@
 
 use super::super::message::RequestMessage;
 use ccore::UnverifiedTransaction;
-use ctypes::{BlockHash, Header};
-use std::collections::{HashMap, HashSet};
+use ctypes::BlockHash;
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::mem::replace;
 
-#[derive(Clone)]
-struct Target {
-    hash: BlockHash,
-    is_empty: bool,
+#[derive(Debug, PartialEq)]
+enum State {
+    Queued,
+    Downloading,
+    Downloaded {
+        transactions: Vec<UnverifiedTransaction>,
+    },
+    Drained,
+}
+
+impl Default for State {
+    fn default() -> Self {
+        State::Queued
+    }
 }
 
 #[derive(Default)]
 pub struct BodyDownloader {
-    targets: Vec<Target>,
-    downloading: HashSet<BlockHash>,
-    downloaded: HashMap<BlockHash, Vec<UnverifiedTransaction>>,
+    targets: Vec<BlockHash>,
+    states: HashMap<BlockHash, State>,
 }
 
 impl BodyDownloader {
@@ -37,9 +48,12 @@ impl BodyDownloader {
         const MAX_BODY_REQEUST_LENGTH: usize = 128;
         let mut hashes = Vec::new();
         for t in &self.targets {
-            if !self.downloading.contains(&t.hash) && !self.downloaded.contains_key(&t.hash) {
-                hashes.push(t.hash);
+            let state = self.states.entry(*t).or_default();
+            if *state != State::Queued {
+                continue
             }
+            *state = State::Downloading;
+            hashes.push(*t);
             if hashes.len() >= MAX_BODY_REQEUST_LENGTH {
                 break
             }
@@ -47,101 +61,99 @@ impl BodyDownloader {
         if hashes.is_empty() {
             None
         } else {
-            self.downloading.extend(&hashes);
             Some(RequestMessage::Bodies(hashes))
         }
     }
 
     pub fn import_bodies(&mut self, hashes: Vec<BlockHash>, bodies: Vec<Vec<UnverifiedTransaction>>) {
-        let empty_targets: HashSet<_> = self.targets.iter().filter(|t| t.is_empty).map(|t| t.hash).collect();
-        for (hash, body) in hashes.into_iter().zip(bodies) {
-            if self.downloading.remove(&hash) {
-                if body.is_empty() {
-                    if !empty_targets.contains(&hash) {
-                        cwarn!(SYNC, "Invalid body of {}. It should be not empty.", hash);
-                        continue
-                    }
-                } else if empty_targets.contains(&hash) {
-                    cwarn!(SYNC, "Invalid body of {}. It should be empty.", hash);
+        assert_eq!(hashes.len(), bodies.len());
+        for (hash, transactions) in hashes.into_iter().zip(bodies) {
+            if let Some(state) = self.states.get_mut(&hash) {
+                if state != &State::Downloading {
                     continue
                 }
-                self.downloaded.insert(hash, body);
+                *state = State::Downloaded {
+                    transactions,
+                }
             }
         }
-        self.downloading.shrink_to_fit();
     }
 
     pub fn get_target_hashes(&self) -> Vec<BlockHash> {
-        self.targets.iter().map(|t| t.hash).collect()
+        self.targets.iter().map(Clone::clone).collect()
     }
 
-    pub fn add_target(&mut self, header: &Header) {
-        cdebug!(SYNC, "Add download target: {}", header.hash());
-        self.targets.push(Target {
-            hash: header.hash(),
-            is_empty: header.is_empty(),
-        });
+    pub fn add_targets(&mut self, hashes: Vec<BlockHash>) {
+        cdebug!(SYNC, "Add download targets: {:?}", hashes);
+        for hash in &hashes {
+            self.states.insert(*hash, State::Queued);
+        }
+        self.targets.extend(hashes);
     }
 
-    pub fn remove_target(&mut self, targets: &[BlockHash]) {
+    pub fn remove_targets(&mut self, targets: &[BlockHash]) {
         if targets.is_empty() {
             return
         }
         cdebug!(SYNC, "Remove download targets: {:?}", targets);
-        for hash in targets {
-            if let Some(index) = self.targets.iter().position(|t| t.hash == *hash) {
-                self.targets.remove(index);
-            }
-            self.downloading.remove(hash);
-            self.downloaded.remove(hash);
-        }
+        // XXX: It can be slow.
+        self.states.retain(|hash, _| !targets.contains(hash));
+        self.targets.retain(|hash| !targets.contains(hash));
+        self.states.shrink_to_fit();
         self.targets.shrink_to_fit();
-        self.downloading.shrink_to_fit();
-        self.downloaded.shrink_to_fit();
     }
 
     pub fn reset_downloading(&mut self, hashes: &[BlockHash]) {
         cdebug!(SYNC, "Remove downloading by timeout {:?}", hashes);
         for hash in hashes {
-            self.downloading.remove(&hash);
+            if let Some(state) = self.states.get_mut(hash) {
+                if *state == State::Downloading {
+                    *state = State::Queued;
+                }
+            }
         }
-        self.downloading.shrink_to_fit();
     }
 
     pub fn drain(&mut self) -> Vec<(BlockHash, Vec<UnverifiedTransaction>)> {
         let mut result = Vec::new();
-        for t in &self.targets {
-            if let Some(body) = self.downloaded.remove(&t.hash) {
-                result.push((t.hash, body));
-            } else {
-                break
+        for hash in &self.targets {
+            let entry = self.states.entry(*hash);
+            let state = match entry {
+                Entry::Vacant(_) => unreachable!(),
+                Entry::Occupied(mut entry) => match entry.get_mut() {
+                    state @ State::Downloaded {
+                        ..
+                    } => replace(state, State::Drained),
+                    _ => break,
+                },
+            };
+            match state {
+                State::Downloaded {
+                    transactions,
+                } => {
+                    result.push((*hash, transactions));
+                }
+                _ => unreachable!(),
             }
         }
-        self.downloaded.shrink_to_fit();
-        self.targets.drain(0..result.len());
-        self.targets.shrink_to_fit();
         result
     }
 
-    pub fn re_request(
-        &mut self,
-        hash: BlockHash,
-        is_empty: bool,
-        remains: Vec<(BlockHash, Vec<UnverifiedTransaction>)>,
-    ) {
-        let mut new_targets = vec![Target {
-            hash,
-            is_empty,
-        }];
-        new_targets.extend(remains.into_iter().map(|(hash, transactions)| {
-            let is_empty = transactions.is_empty();
-            self.downloaded.insert(hash, transactions);
-            Target {
-                hash,
-                is_empty,
-            }
-        }));
-        new_targets.append(&mut self.targets);
-        self.targets = new_targets;
+    pub fn re_request(&mut self, hash: BlockHash, remains: Vec<(BlockHash, Vec<UnverifiedTransaction>)>) {
+        #[inline]
+        fn insert(states: &mut HashMap<BlockHash, State>, hash: BlockHash, state: State) {
+            let old = states.insert(hash, state);
+            debug_assert_ne!(None, old);
+        }
+        // The implementation of extend method allocates an additional memory for new items.
+        // However, our implementation guarantees that new items are already in the map and it just
+        // update the states. So iterating over new items and calling the insert method is faster
+        // than using the extend method and uses less memory.
+        for (hash, transactions) in remains {
+            insert(&mut self.states, hash, State::Downloaded {
+                transactions,
+            });
+        }
+        insert(&mut self.states, hash, State::Queued);
     }
 }
diff --git a/sync/src/block/extension.rs b/sync/src/block/extension.rs
index 4d670674a6..1ab792126f 100644
--- a/sync/src/block/extension.rs
+++ b/sync/src/block/extension.rs
@@ -223,11 +223,17 @@ impl Extension {
             }
         }
         let mut body_downloader = BodyDownloader::default();
-        for neighbors in hollow_headers.windows(2).rev() {
-            let child = &neighbors[0];
-            cdebug!(SYNC, "Adding block #{} (hash: {}) for initial body download target", child.number(), child.hash());
-            body_downloader.add_target(child);
-        }
+        let new_targets = hollow_headers
+            .windows(2)
+            .rev()
+            .map(|neighbors| {
+                let child = &neighbors[0];
+                let hash = child.hash();
+                cdebug!(SYNC, "Adding block #{} (hash: {}) for initial body download target", child.number(), hash);
+                hash
+            })
+            .collect();
+        body_downloader.add_targets(new_targets);
         cinfo!(SYNC, "Sync extension initialized");
         Extension {
             state,
@@ -715,15 +721,13 @@ impl Extension {
                 .into_iter()
                 .filter(|header| self.client.block_body(&BlockId::Hash(header.hash())).is_none())
                 .collect(); // FIXME: No need to collect here if self is not borrowed.
-            for header in headers {
-                self.body_downloader.add_target(&header.decode());
-            }
+            self.body_downloader.add_targets(headers.into_iter().map(|header| header.hash()).collect());
         }
     }
 
     fn new_blocks(&mut self, imported: Vec<BlockHash>, invalid: Vec<BlockHash>) {
-        self.body_downloader.remove_target(&imported);
-        self.body_downloader.remove_target(&invalid);
+        self.body_downloader.remove_targets(&imported);
+        self.body_downloader.remove_targets(&invalid);
 
         self.send_status_broadcast();
     }
@@ -1038,6 +1042,7 @@ impl Extension {
     }
 
     fn import_blocks(&mut self, blocks: Vec<(BlockHash, Vec<UnverifiedTransaction>)>) {
+        let mut imported = Vec::new();
         let mut remains = Vec::new();
         let mut error_target = None;
         for (hash, transactions) in blocks {
@@ -1051,7 +1056,7 @@ impl Extension {
                 skewed_merkle_root(BLAKE_NULL_RLP, transactions.iter().map(Encodable::rlp_bytes));
             if *header.transactions_root() != calculated_transactions_root {
                 cwarn!(SYNC, "Received corrupted body for ${}({}", header.number(), hash);
-                error_target = Some((hash, transactions.is_empty()));
+                error_target = Some(hash);
                 continue
             }
 
@@ -1072,12 +1077,15 @@ impl Extension {
                     cwarn!(SYNC, "Cannot import block({}): {:?}", hash, err);
                     break
                 }
-                _ => {}
+                Ok(_) => {
+                    imported.push(hash);
+                }
             }
         }
-        if let Some((hash, is_empty)) = error_target {
-            self.body_downloader.re_request(hash, is_empty, remains);
+        if let Some(hash) = error_target {
+            self.body_downloader.re_request(hash, remains);
         }
+        self.body_downloader.remove_targets(&imported);
     }
 
     fn on_body_response(&mut self, hashes: Vec<BlockHash>, bodies: Vec<Vec<UnverifiedTransaction>>) {