From 7ca4b9da32ebd0e1a1492f163b77d5bdc2efb60a Mon Sep 17 00:00:00 2001
From: Denis Khalikov <dennis.khalikov@gmail.com>
Date: Wed, 27 Dec 2023 09:43:27 +0300
Subject: [PATCH] feat(brm): MCOL-5631 Optimize BRM load operation. (#3085)

---
 versioning/BRM/extentmap.cpp | 64 ++++++++++++++++++------------------
 1 file changed, 32 insertions(+), 32 deletions(-)

diff --git a/versioning/BRM/extentmap.cpp b/versioning/BRM/extentmap.cpp
index a7b7ced4c..bed1f0bce 100644
--- a/versioning/BRM/extentmap.cpp
+++ b/versioning/BRM/extentmap.cpp
@@ -1584,61 +1584,60 @@ void ExtentMap::loadVersion4or5(T* in, bool upgradeV4ToV5)
   constexpr const uint32_t freeShmemThreshold = EM_RB_TREE_INITIAL_SIZE >> 4;
   growEMShmseg(memorySizeNeeded);
 
-  size_t progress = 0, writeSize = emNumElements * sizeof(EMEntry);
   int err;
-  char* writePos;
+  size_t progress = 0;
 
   if (!upgradeV4ToV5)
   {
-    for (uint32_t i = 0; i < emNumElements; ++i)
-    {
-      progress = 0;
-      EMEntry emEntry;
-      writeSize = sizeof(EMEntry);
-      writePos = reinterpret_cast<char*>(&emEntry);
+    const size_t readSize = emNumElements * sizeof(EMEntry);
+    std::unique_ptr<char[]> emBuffer(new char[readSize]);
 
-      while (progress < writeSize)
+    while (progress < readSize)
+    {
+      err = in->read(&emBuffer[progress], readSize - progress);
+      if (err <= 0)
       {
-        err = in->read(writePos + progress, writeSize - progress);
-        if (err <= 0)
-        {
-          log_errno("ExtentMap::loadVersion4(): read ");
-          throw runtime_error("ExtentMap::loadVersion4(): read failed. Check the error log.");
-        }
-        progress += (uint)err;
+        log_errno("ExtentMap::loadVersion4(): read ");
+        throw runtime_error("ExtentMap::loadVersion4(): read failed. Check the error log.");
       }
+      progress += (uint)err;
+    }
+
+    progress = 0;
+    for (uint32_t emIndex = 0; emIndex < emNumElements; ++emIndex)
+    {
       if (fPExtMapRBTreeImpl->getFreeMemory() < freeShmemThreshold)
         growEMShmseg(EM_RB_TREE_INCREMENT);
 
+      EMEntry emEntry = *reinterpret_cast<EMEntry*>(&emBuffer[progress]);
       std::pair<int64_t, EMEntry> lbidEMEntryPair = make_pair(emEntry.range.start, emEntry);
       fExtentMapRBTree->insert(lbidEMEntryPair);
+      progress += sizeof(EMEntry);
     }
   }
   else
   {
-    // We are upgrading extent map from v4 to v5.
-    for (uint32_t i = 0; i < emNumElements; i++)
+    const size_t readSize = emNumElements * sizeof(EMEntry_v4);
+    std::unique_ptr<char[]> emBuffer(new char[readSize]);
+
+    while (progress < readSize)
     {
-      EMEntry_v4 emEntryV4;
-      progress = 0;
-      writeSize = sizeof(EMEntry_v4);
-      writePos = reinterpret_cast<char*>(&emEntryV4);
-
-      while (progress < writeSize)
+      err = in->read(&emBuffer[progress], readSize - progress);
+      if (err <= 0)
       {
-        err = in->read(writePos + progress, writeSize - progress);
-        if (err <= 0)
-        {
-          log_errno("ExtentMap::loadVersion4or5(): read ");
-          throw runtime_error(
-              "ExtentMap::loadVersion4or5(): read failed during upgrade. Check the error log.");
-        }
-        progress += (uint)err;
+        log_errno("ExtentMap::loadVersion4(): read ");
+        throw runtime_error("ExtentMap::loadVersion4(): read failed. Check the error log.");
       }
+      progress += (uint)err;
+    }
 
+    progress = 0;
+    for (uint32_t emIndex = 0; emIndex < emNumElements; ++emIndex)
+    {
       if (fPExtMapRBTreeImpl->getFreeMemory() < freeShmemThreshold)
         growEMShmseg(EM_RB_TREE_INCREMENT);
 
+      EMEntry_v4 emEntryV4 = *reinterpret_cast<EMEntry_v4*>(&emBuffer[progress]);
       EMEntry emEntry;
       emEntry.range.start = emEntryV4.range.start;
       emEntry.range.size = emEntryV4.range.size;
@@ -1657,6 +1656,7 @@ void ExtentMap::loadVersion4or5(T* in, bool upgradeV4ToV5)
 
       std::pair<int64_t, EMEntry> lbidEMEntryPair = make_pair(emEntry.range.start, emEntry);
       fExtentMapRBTree->insert(lbidEMEntryPair);
+      progress += sizeof(EMEntry_v4);
     }
 
     std::cout << emNumElements << " extents successfully upgraded" << std::endl;