Increase minimum debug.log size to 10MB after shrink.

src/init.cpp

@@ -1149,8 +1149,11 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
 #ifndef WIN32
     CreatePidFile(GetPidFile(), getpid());
 #endif
-    if (GetBoolArg("-shrinkdebugfile", !fDebug))
+    if (GetBoolArg("-shrinkdebugfile", !fDebug)) {
+        // Do this first since it both loads a bunch of debug.log into memory,
+        // and because this needs to happen before any other debug.log printing
         ShrinkDebugFile();
+    }
 
     if (fPrintToDebugLog)
         OpenDebugLog();

src/util.cpp

@@ -723,13 +723,17 @@ void AllocateFileRange(FILE *file, unsigned int offset, unsigned int length) {
 
 void ShrinkDebugFile()
 {
+    // Amount of debug.log to save at end when shrinking (must fit in memory)
+    constexpr size_t RECENT_DEBUG_HISTORY_SIZE = 10 * 1000000;
     // Scroll debug.log if it's getting too big
     boost::filesystem::path pathLog = GetDataDir() / "debug.log";
     FILE* file = fopen(pathLog.string().c_str(), "r");
-    if (file && boost::filesystem::file_size(pathLog) > 10 * 1000000)
+    // If debug.log file is more than 10% bigger the RECENT_DEBUG_HISTORY_SIZE
+    // trim it down by saving only the last RECENT_DEBUG_HISTORY_SIZE bytes
+    if (file && boost::filesystem::file_size(pathLog) > 11 * (RECENT_DEBUG_HISTORY_SIZE / 10))
     {
         // Restart the file with some of the end
-        std::vector <char> vch(200000,0);
+        std::vector<char> vch(RECENT_DEBUG_HISTORY_SIZE, 0);
         fseek(file, -((long)vch.size()), SEEK_END);
         int nBytes = fread(vch.data(), 1, vch.size(), file);
         fclose(file);