From 4f5bb798e7fdb7ea8bb32171b2696e085da604b8 Mon Sep 17 00:00:00 2001
From: "Wladimir J. van der Laan" <laanwj@gmail.com>
Date: Tue, 19 Apr 2016 10:44:44 +0200
Subject: [PATCH] Merge #7827: Speed up getchaintips.

87049e8 Speed up getchaintips. (mrbandrews)
---
 src/rpc/blockchain.cpp | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index ae0ec226dd136..a0bd85a21cb35 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -959,17 +959,30 @@ UniValue getchaintips(const UniValue& params, bool fHelp)
 
     LOCK(cs_main);
 
-    /* Build up a list of chain tips.  We start with the list of all
-       known blocks, and successively remove blocks that appear as pprev
-       of another block.  */
+    /*
+     * Idea:  the set of chain tips is chainActive.tip, plus orphan blocks which do not have another orphan building off of them. 
+     * Algorithm:
+     *  - Make one pass through mapBlockIndex, picking out the orphan blocks, and also storing a set of the orphan block's pprev pointers.
+     *  - Iterate through the orphan blocks. If the block isn't pointed to by another orphan, it is a chain tip.
+     *  - add chainActive.Tip()
+     */
     std::set<const CBlockIndex*, CompareBlocksByHeight> setTips;
-    BOOST_FOREACH(const PAIRTYPE(const uint256, CBlockIndex*)& item, mapBlockIndex)
-        setTips.insert(item.second);
+    std::set<const CBlockIndex*> setOrphans;
+    std::set<const CBlockIndex*> setPrevs;
+
     BOOST_FOREACH(const PAIRTYPE(const uint256, CBlockIndex*)& item, mapBlockIndex)
     {
-        const CBlockIndex* pprev = item.second->pprev;
-        if (pprev)
-            setTips.erase(pprev);
+        if (!chainActive.Contains(item.second)) {
+            setOrphans.insert(item.second);
+            setPrevs.insert(item.second->pprev);
+        }
+    }
+
+    for (std::set<const CBlockIndex*>::iterator it = setOrphans.begin(); it != setOrphans.end(); ++it)
+    {
+        if (setPrevs.erase(*it) == 0) {
+            setTips.insert(*it);
+        }
     }
 
     // Always report the currently active tip.