From dd679142594916044314304a15a9d3b523b3e712 Mon Sep 17 00:00:00 2001
From: Peter Shugalev <peter@shugalev.com>
Date: Mon, 15 Apr 2024 10:17:16 +0200
Subject: [PATCH] Optimize loading block index guts if low on memory (Linux
 only)

---
 src/txdb.cpp | 14 +++++++++++++-
 src/txdb.h   |  2 ++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/src/txdb.cpp b/src/txdb.cpp
index e554c15de0..acb6463381 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -17,6 +17,10 @@
 
 #include <boost/thread.hpp>
 
+#ifdef __linux__
+#include <sys/sysinfo.h>
+#endif
+
 static const char DB_COIN = 'C';
 static const char DB_COINS = 'c';
 static const char DB_BLOCK_FILES = 'f';
@@ -365,6 +369,14 @@ bool CBlockTreeDB::LoadBlockIndexGuts(boost::function<CBlockIndex*(const uint256
     int firstInLastNBlocksHeight = 0;
 
     bool fCheckPoWForAllBlocks = GetBoolArg("-fullblockindexcheck", DEFAULT_FULL_BLOCKINDEX_CHECK);
+    int64_t nBlocksToCheck = GetArg("-numberofblockstocheckonstartup", DEFAULT_BLOCKINDEX_NUMBER_OF_BLOCKS_TO_CHECK);
+
+#ifdef __linux__
+    struct sysinfo sysInfo;
+
+    if (sysinfo(&sysInfo) == 0 && sysInfo.freeram < 2ul*1024ul*1024ul*1024ul)
+        nBlocksToCheck = DEFAULT_BLOCKINDEX_LOWMEM_NUMBER_OF_BLOCKS_TO_CHECK;
+#endif
 
     while (pcursor->Valid()) {
         boost::this_thread::interruption_point();
@@ -423,7 +435,7 @@ bool CBlockTreeDB::LoadBlockIndexGuts(boost::function<CBlockIndex*(const uint256
                 else {
                     if (pindexNew->nHeight >= firstInLastNBlocksHeight) {
                         lastNBlocks.insert(std::pair<int, CBlockIndex*>(pindexNew->nHeight, pindexNew));
-                        if (lastNBlocks.size() > DEFAULT_BLOCKINDEX_NUMBER_OF_BLOCKS_TO_CHECK) {
+                        if (lastNBlocks.size() > nBlocksToCheck) {
                             // pop the first element from the map
                             auto firstElement = lastNBlocks.begin();
                             auto elementToPop = firstElement++;
diff --git a/src/txdb.h b/src/txdb.h
index 591a4e9987..fb35aa4c9f 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -47,6 +47,8 @@ static const int64_t nMaxCoinsDBCache = 8;
 static const bool DEFAULT_FULL_BLOCKINDEX_CHECK = false;
 //! If not doing full check of block index, check only N of the latest blocks
 static const int DEFAULT_BLOCKINDEX_NUMBER_OF_BLOCKS_TO_CHECK = 10000;
+//! Check fewer blocks if low on memory
+static const int DEFAULT_BLOCKINDEX_LOWMEM_NUMBER_OF_BLOCKS_TO_CHECK = 50;
 
 struct CDiskTxPos : public CDiskBlockPos
 {