diff --git a/lib/blockchain/chaindb.js b/lib/blockchain/chaindb.js
index 0fd11349..6a525bd7 100644
--- a/lib/blockchain/chaindb.js
+++ b/lib/blockchain/chaindb.js
@@ -84,7 +84,7 @@ ChainDB.prototype.open = async function open() {
   this.logger.info('Opening ChainDB...');
 
   await this.db.open();
-  await this.db.checkVersion('V', 3);
+  await this.db.checkVersion('V', 4);
 
   state = await this.getState();
 
@@ -1685,23 +1685,19 @@ ChainDB.prototype.removeBlock = async function removeBlock(entry) {
 
 ChainDB.prototype.saveView = function saveView(view) {
   for (let [hash, coins] of view.map) {
-    for (let i = 0; i < coins.outputs.length; i++) {
-      let coin = coins.outputs[i];
+    for (let [index, coin] of coins.outputs) {
       let raw;
 
-      if (!coin)
-        continue;
-
       if (coin.spent) {
-        this.del(layout.c(hash, i));
-        this.coinCache.unpush(hash + i);
+        this.del(layout.c(hash, index));
+        this.coinCache.unpush(hash + index);
         continue;
       }
 
       raw = coin.toRaw();
 
-      this.put(layout.c(hash, i), raw);
-      this.coinCache.push(hash + i, raw);
+      this.put(layout.c(hash, index), raw);
+      this.coinCache.push(hash + index, raw);
     }
   }
 };
diff --git a/lib/coins/coins.js b/lib/coins/coins.js
index 38d5a577..37c0b547 100644
--- a/lib/coins/coins.js
+++ b/lib/coins/coins.js
@@ -21,7 +21,7 @@ function Coins(options) {
   if (!(this instanceof Coins))
     return new Coins(options);
 
-  this.outputs = [];
+  this.outputs = new Map();
 }
 
 /**
@@ -33,12 +33,9 @@ function Coins(options) {
 Coins.prototype.add = function add(index, coin) {
   assert(index >= 0);
 
-  while (this.outputs.length <= index)
-    this.outputs.push(null);
+  assert(!this.outputs.has(index));
 
-  assert(!this.outputs[index]);
-
-  this.outputs[index] = coin;
+  this.outputs.set(index, coin);
 };
 
 /**
@@ -69,10 +66,7 @@ Coins.prototype.addCoin = function addCoin(coin) {
  */
 
 Coins.prototype.has = function has(index) {
-  if (index >= this.outputs.length)
-    return false;
-
-  return this.outputs[index] != null;
+  return this.outputs.has(index);
 };
 
 /**
@@ -82,12 +76,7 @@ Coins.prototype.has = function has(index) {
  */
 
 Coins.prototype.isUnspent = function isUnspent(index) {
-  let coin;
-
-  if (index >= this.outputs.length)
-    return false;
-
-  coin = this.outputs[index];
+  let coin = this.outputs.get(index);
 
   if (!coin || coin.spent)
     return false;
@@ -102,10 +91,7 @@ Coins.prototype.isUnspent = function isUnspent(index) {
  */
 
 Coins.prototype.get = function get(index) {
-  if (index >= this.outputs.length)
-    return;
-
-  return this.outputs[index];
+  return this.outputs.get(index);
 };
 
 /**
@@ -115,10 +101,12 @@ Coins.prototype.get = function get(index) {
  */
 
 Coins.prototype.getOutput = function getOutput(index) {
-  if (index >= this.outputs.length)
+  let coin = this.outputs.get(index);
+
+  if (!coin)
     return;
 
-  return this.outputs[index].output;
+  return coin.output;
 };
 
 /**
@@ -128,10 +116,12 @@ Coins.prototype.getOutput = function getOutput(index) {
  */
 
 Coins.prototype.getCoin = function getCoin(prevout) {
-  if (prevout.index >= this.outputs.length)
+  let coin = this.outputs.get(prevout.index);
+
+  if (!coin)
     return;
 
-  return this.outputs[prevout.index].toCoin(prevout);
+  return coin.toCoin(prevout);
 };
 
 /**
@@ -163,8 +153,7 @@ Coins.prototype.remove = function remove(index) {
   if (!coin)
     return false;
 
-  this.outputs[index] = null;
-  this.cleanup();
+  this.outputs.delete(index);
 
   return coin;
 };
@@ -175,25 +164,16 @@ Coins.prototype.remove = function remove(index) {
  */
 
 Coins.prototype.length = function length() {
-  let len = this.outputs.length;
+  let len = -1;
 
-  while (len > 0 && !this.isUnspent(len - 1))
-    len--;
+  for (let [index, coin] of this.outputs) {
+    if (!coin.spent) {
+      if (index > len)
+        len = index;
+    }
+  }
 
-  return len;
-};
-
-/**
- * Cleanup spent outputs (remove pruned).
- */
-
-Coins.prototype.cleanup = function cleanup() {
-  let len = this.outputs.length;
-
-  while (len > 0 && !this.outputs[len - 1])
-    len--;
-
-  this.outputs.length = len;
+  return len + 1;
 };
 
 /**
@@ -202,7 +182,7 @@ Coins.prototype.cleanup = function cleanup() {
  */
 
 Coins.prototype.isEmpty = function isEmpty() {
-  return this.length() === 0;
+  return this.outputs.size === 0;
 };
 
 /**
@@ -218,16 +198,12 @@ Coins.prototype.fromTX = function fromTX(tx, height) {
   for (let i = 0; i < tx.outputs.length; i++) {
     let output = tx.outputs[i];
 
-    if (output.script.isUnspendable()) {
-      this.outputs.push(null);
+    if (output.script.isUnspendable())
       continue;
-    }
 
-    this.outputs.push(CoinEntry.fromTX(tx, i, height));
+    this.outputs.set(i, CoinEntry.fromTX(tx, i, height));
   }
 
-  this.cleanup();
-
   return this;
 };
 
diff --git a/lib/coins/coinview.js b/lib/coins/coinview.js
index e6835fbb..e8dec2d4 100644
--- a/lib/coins/coinview.js
+++ b/lib/coins/coinview.js
@@ -93,7 +93,7 @@ CoinView.prototype.addTX = function addTX(tx, height) {
 CoinView.prototype.removeTX = function removeTX(tx, height) {
   let coins = Coins.fromTX(tx, height);
 
-  for (let coin of coins.outputs)
+  for (let coin of coins.outputs.values())
     coin.spent = true;
 
   return this.add(tx.hash('hex'), coins);
@@ -173,12 +173,7 @@ CoinView.prototype.addOutput = function addOutput(prevout, output) {
  */
 
 CoinView.prototype.spendOutput = function spendOutput(prevout) {
-  let coins = this.get(prevout.hash);
-
-  if (!coins)
-    return false;
-
-  return this.spendFrom(coins, prevout.index);
+  return this.spend(prevout.hash, prevout.index);
 };
 
 /**
@@ -198,12 +193,17 @@ CoinView.prototype.removeOutput = function removeOutput(prevout) {
 
 /**
  * Spend a coin from coins object.
- * @param {Coins} coins
+ * @param {Hash} hash
  * @param {Number} index
  * @returns {Boolean}
  */
 
-CoinView.prototype.spendFrom = function spendFrom(coins, index) {
+CoinView.prototype.spend = function spend(hash, index) {
+  let coins = this.get(hash);
+
+  if (!coins)
+    return false;
+
   let coin = coins.spend(index);
 
   if (!coin)
@@ -313,19 +313,20 @@ CoinView.prototype.isCoinbase = function isCoinbase(input) {
  */
 
 CoinView.prototype.readCoin = async function readCoin(db, input) {
-  let coin = this.hasEntry(input);
+  let coin = this.getEntry(input);
   let prevout = input.prevout;
 
-  if (!coin) {
-    coin = await db.readCoin(prevout);
+  if (coin)
+    return coin;
 
-    if (!coin)
-      return;
+  coin = await db.readCoin(prevout);
 
-    return this.addEntry(prevout, coin);
-  }
+  if (!coin)
+    return null;
 
-  return this.get(prevout.hash);
+  this.addEntry(prevout, coin);
+
+  return coin;
 };
 
 /**
@@ -336,7 +337,7 @@ CoinView.prototype.readCoin = async function readCoin(db, input) {
  * @returns {Promise} - Returns {Boolean}.
  */
 
-CoinView.prototype.ensureInputs = async function ensureInputs(db, tx) {
+CoinView.prototype.readInputs = async function readInputs(db, tx) {
   let found = true;
 
   for (let input of tx.inputs) {
@@ -356,33 +357,39 @@ CoinView.prototype.ensureInputs = async function ensureInputs(db, tx) {
  */
 
 CoinView.prototype.spendInputs = async function spendInputs(db, tx) {
+  if (tx.inputs.length < 4) {
+    let jobs = [];
+    let coins;
+
+    for (let input of tx.inputs)
+      jobs.push(this.readCoin(db, input));
+
+    coins = await Promise.all(jobs);
+
+    for (let coin of coins) {
+      if (!coin || coin.spent)
+        return false;
+
+      coin.spent = true;
+      this.undo.push(coin);
+    }
+
+    return true;
+  }
+
   for (let input of tx.inputs) {
-    let coins = await this.readCoin(db, input);
+    let coin = await this.readCoin(db, input);
 
-    if (!coins)
+    if (!coin || coin.spent)
       return false;
 
-    if (!this.spendFrom(coins, input.prevout.index))
-      return false;
+    coin.spent = true;
+    this.undo.push(coin);
   }
 
   return true;
 };
 
-/**
- * Convert collection to an array.
- * @returns {Coins[]}
- */
-
-CoinView.prototype.toArray = function toArray() {
-  let out = [];
-
-  for (let coins of this.map.values())
-    out.push(coins);
-
-  return out;
-};
-
 /**
  * Calculate serialization size.
  * @returns {Number}
diff --git a/test/coins-test.js b/test/coins-test.js
index cc9de450..7d4c1468 100644
--- a/test/coins-test.js
+++ b/test/coins-test.js
@@ -38,7 +38,7 @@ describe('Coins', function() {
     view.addTX(tx1, 1);
 
     coins = view.get(hash);
-    assert.equal(coins.outputs.length, tx1.outputs.length);
+    assert.equal(coins.outputs.size, tx1.outputs.length);
 
     entry = coins.get(0);
     assert(entry);
@@ -103,7 +103,7 @@ describe('Coins', function() {
     coins = res.get(prev.hash);
 
     assert.strictEqual(coins.length(), 2);
-    assert.strictEqual(coins.get(0), null);
+    assert.strictEqual(coins.get(0), undefined);
     deepCoinsEqual(coins.get(1), reserialize(coins.get(1)));
   });
 });