From 2bf6eb1c7cec5fd2294ec71f0c395a4ae1fd9093 Mon Sep 17 00:00:00 2001
From: Alexander Block <ablock84@gmail.com>
Date: Tue, 22 Jan 2019 14:18:34 +0100
Subject: [PATCH] Track parent->child relations for blocks

Allows to cheaply find all possible children of a block.
---
 src/validation.cpp | 11 +++++++++++
 src/validation.h   |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/src/validation.cpp b/src/validation.cpp
index 87647dae7b..b020fa1e43 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -68,6 +68,7 @@
 CCriticalSection cs_main;
 
 BlockMap mapBlockIndex;
+PrevBlockMap mapPrevBlockIndex;
 CChain chainActive;
 CBlockIndex *pindexBestHeader = NULL;
 CWaitableCriticalSection csBestBlock;
@@ -3042,6 +3043,11 @@ CBlockIndex* AddToBlockIndex(const CBlockHeader& block)
 
     setDirtyBlockIndex.insert(pindexNew);
 
+    // track prevBlockHash -> pindex (multimap)
+    if (pindexNew->pprev) {
+        mapPrevBlockIndex.emplace(pindexNew->pprev->GetBlockHash(), pindexNew);
+    }
+
     return pindexNew;
 }
 
@@ -3827,6 +3833,11 @@ bool static LoadBlockIndexDB(const CChainParams& chainparams)
     {
         CBlockIndex* pindex = item.second;
         vSortedByHeight.push_back(std::make_pair(pindex->nHeight, pindex));
+
+        // build mapPrevBlockIndex
+        if (pindex->pprev) {
+            mapPrevBlockIndex.emplace(pindex->pprev->GetBlockHash(), pindex);
+        }
     }
     sort(vSortedByHeight.begin(), vSortedByHeight.end());
     BOOST_FOREACH(const PAIRTYPE(int, CBlockIndex*)& item, vSortedByHeight)
diff --git a/src/validation.h b/src/validation.h
index 2577a8a007..5dc3c16545 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -157,7 +157,9 @@ extern CScript COINBASE_FLAGS;
 extern CCriticalSection cs_main;
 extern CTxMemPool mempool;
 typedef boost::unordered_map<uint256, CBlockIndex*, BlockHasher> BlockMap;
+typedef std::unordered_multimap<uint256, CBlockIndex*, BlockHasher> PrevBlockMap;
 extern BlockMap mapBlockIndex;
+extern PrevBlockMap mapPrevBlockIndex;
 extern uint64_t nLastBlockTx;
 extern uint64_t nLastBlockSize;
 extern const std::string strMessageMagic;