From 210ce4c7676adebeeb62dd7375e47fc40a7a10f5 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Sun, 5 Mar 2017 02:03:14 -0800
Subject: [PATCH] mempool: evict by lowest fee rate.

---
 lib/mempool/mempool.js      | 109 +++++++++++++++++++++++++++---------
 lib/mempool/mempoolentry.js |  10 ++++
 2 files changed, 92 insertions(+), 27 deletions(-)

diff --git a/lib/mempool/mempool.js b/lib/mempool/mempool.js
index 8e59a38c..674022a5 100644
--- a/lib/mempool/mempool.js
+++ b/lib/mempool/mempool.js
@@ -31,6 +31,7 @@ var Fees = require('./fees');
 var Map = require('../utils/map');
 var CoinView = require('../coins/coinview');
 var Coins = require('../coins/coins');
+var Heap = require('../utils/heap');
 var VerifyError = errors.VerifyError;
 var VerifyResult = errors.VerifyResult;
 
@@ -357,58 +358,74 @@ Mempool.prototype._reset = co(function* reset() {
 });
 
 /**
- * Ensure the size of the mempool stays below 300mb.
- * @param {Hash} entryHash - TX that initiated the trim.
+ * Ensure the size of the mempool stays below `maxSize`.
+ * Evicts entries by timestamp and cumulative fee rate.
+ * @param {MempoolEntry} added
  * @returns {Promise}
  */
 
-Mempool.prototype.limitSize = function limitSize(entryHash) {
+Mempool.prototype.limitSize = function limitSize(added) {
+  var maxSize = this.options.maxSize;
+  var expiryTime = this.options.expiryTime;
+  var now = util.now();
   var trimmed = false;
-  var i, hashes, hash, end, entry;
+  var i, queue, entry, keys, hash, start;
 
-  if (this.getSize() <= this.options.maxSize)
+  if (this.size <= maxSize)
     return trimmed;
 
-  hashes = this.getSnapshot();
-  end = util.now() - this.options.expiryTime;
+  queue = new Heap(cmpRate);
+  keys = this.getSnapshot();
 
-  for (i = 0; i < hashes.length; i++) {
-    hash = hashes[i];
+  start = util.hrtime();
+
+  for (i = 0; i < keys.length; i++) {
+    hash = keys[i];
     entry = this.getEntry(hash);
 
     if (!entry)
       continue;
 
-    if (entry.ts >= end)
+    if (now < entry.ts + expiryTime) {
+      queue.insert(entry);
       continue;
+    }
 
-    if (!trimmed && hash === entryHash)
+    if (entry === added)
       trimmed = true;
 
     this.evictEntry(entry);
-
-    if (this.getSize() <= this.options.maxSize)
-      return trimmed;
   }
 
-  hashes = this.getSnapshot();
+  if (this.size <= maxSize)
+    return trimmed;
 
-  for (i = 0; i < hashes.length; i++) {
-    hash = hashes[i];
-    entry = this.getEntry(hash);
+  this.logger.debug(
+    '(bench) Heap mempool traversal: %d.',
+    util.hrtime(start));
 
-    if (!entry)
+  start = util.hrtime();
+
+  while (queue.size() > 0) {
+    entry = queue.shift();
+    hash = entry.hash('hex');
+
+    if (!this.hasTX(hash))
       continue;
 
-    if (!trimmed && hash === entryHash)
-      trimmed = true;
-
     this.evictEntry(entry);
 
-    if (this.getSize() <= this.options.maxSize)
-      return trimmed;
+    if (entry === added)
+      trimmed = true;
+
+    if (this.size <= maxSize - (maxSize / 10))
+      break;
   }
 
+  this.logger.debug(
+    '(bench) Heap mempool map removal: %d.',
+    util.hrtime(start));
+
   return trimmed;
 };
 
@@ -860,7 +877,7 @@ Mempool.prototype.insertTX = co(function* insertTX(tx) {
   yield this.addEntry(entry, view);
 
   // Trim size if we're too big.
-  if (this.limitSize(hash)) {
+  if (this.limitSize(entry)) {
     throw new VerifyError(tx,
       'insufficientfee',
       'mempool full',
@@ -1084,7 +1101,9 @@ Mempool.prototype.addEntry = co(function* addEntry(entry, view) {
   if (this.fees)
     this.fees.processTX(entry, this.chain.synced);
 
-  this.logger.debug('Added tx %s to mempool.', tx.txid());
+  this.logger.debug(
+    'Added %s to mempool (txs=%d).',
+    tx.txid(), this.totalTX);
 
   this.cache.save(entry);
 
@@ -1517,7 +1536,9 @@ Mempool.prototype.handleOrphans = co(function* handleOrphans(tx) {
       throw err;
     }
 
-    this.logger.debug('Resolved orphan %s in mempool.', orphan.txid());
+    this.logger.debug(
+      'Resolved orphan %s in mempool (txs=%d).',
+      orphan.txid(), this.totalTX);
   }
 
   return resolved;
@@ -2517,6 +2538,40 @@ function removeFee(parent, child) {
   parent.descSize -= child.descSize;
 }
 
+function cmpRate(a, b) {
+  var xf = a.fee;
+  var xs = a.size;
+  var yf = b.fee;
+  var ys = b.size;
+  var x, y;
+
+  if (useDesc(a)) {
+    xf = a.descFee;
+    xs = a.descSize;
+  }
+
+  if (useDesc(b)) {
+    yf = b.descFee;
+    ys = b.descSize;
+  }
+
+  x = xf * ys;
+  y = xs * yf;
+
+  if (x === y) {
+    x = a.ts;
+    y = b.ts;
+  }
+
+  return x - y;
+}
+
+function useDesc(a) {
+  var x = a.fee * a.descSize;
+  var y = a.descFee * a.size;
+  return y > x;
+}
+
 /*
  * Expose
  */
diff --git a/lib/mempool/mempoolentry.js b/lib/mempool/mempoolentry.js
index c9a3832b..00679d52 100644
--- a/lib/mempool/mempoolentry.js
+++ b/lib/mempool/mempoolentry.js
@@ -132,6 +132,16 @@ MempoolEntry.fromTX = function fromTX(tx, view, height) {
   return new MempoolEntry().fromTX(tx, view, height);
 };
 
+/**
+ * Calculate transaction hash.
+ * @param {String?} enc
+ * @returns {Hash}
+ */
+
+MempoolEntry.prototype.hash = function hash(enc) {
+  return this.tx.hash(enc);
+};
+
 /**
  * Calculate priority, taking into account
  * the entry height delta, modified size,