From 0a0b35f685caa02fa386b1105ba626c29084ff42 Mon Sep 17 00:00:00 2001
From: Dan Engelbrecht <dan.engelbrecht@epicgames.com>
Date: Tue, 4 Nov 2025 11:00:58 +0100
Subject: refactor MergeChunkedFolderContents to not reallocate
 Result.ChunkedContent.ChunkOrders for each path added (#626)

---
 src/zenremotestore/chunking/chunkedcontent.cpp | 44 ++++++++++++++++++++------
 1 file changed, 35 insertions(+), 9 deletions(-)

(limited to 'src')

diff --git a/src/zenremotestore/chunking/chunkedcontent.cpp b/src/zenremotestore/chunking/chunkedcontent.cpp
index ea67e3d94..5e6cb9ba5 100644
--- a/src/zenremotestore/chunking/chunkedcontent.cpp
+++ b/src/zenremotestore/chunking/chunkedcontent.cpp
@@ -33,7 +33,6 @@ namespace {
 	{
 		ZEN_ASSERT(ChunkHashes.size() == ChunkRawSizes.size());
 		InOutChunkedContent.ChunkCounts.push_back(gsl::narrow<uint32_t>(ChunkSequence.size()));
-		InOutChunkedContent.ChunkOrders.reserve(InOutChunkedContent.ChunkOrders.size() + ChunkSequence.size());
 
 		for (uint32_t ChunkedSequenceIndex : ChunkSequence)
 		{
@@ -122,6 +121,8 @@ namespace {
 						{
 							ChunkSizes.push_back(Source.Size);
 						}
+						OutChunkedContent.ChunkedContent.ChunkOrders.reserve(OutChunkedContent.ChunkedContent.ChunkOrders.size() +
+																			 Chunked.Info.ChunkSequence.size());
 						AddChunkSequence(Stats,
 										 OutChunkedContent.ChunkedContent,
 										 ChunkHashToChunkIndex,
@@ -606,6 +607,19 @@ MergeChunkedFolderContents(const ChunkedFolderContent& Base, std::span<const Chu
 										   std::span<const ChunkedFolderContent>					 Overlays) {
 		const ChunkedContentLookup	OverlayLookup	 = BuildChunkedContentLookup(OverlayContent);
 		tsl::robin_set<std::string> BaseOverlayPaths = BuildOverlayPaths(Overlays);
+
+		struct SequenceToAdd
+		{
+			IoHash					  RawHash;
+			std::span<const uint32_t> OriginalChunkOrder;
+		};
+
+		std::vector<SequenceToAdd> SequencesToAdd;
+
+		size_t ChunkCountsAdded = 0;
+		size_t ChunkOrdersAdded = 0;
+
+		ChunkingStatistics Stats;
 		for (uint32_t PathIndex = 0; PathIndex < OverlayContent.Paths.size(); PathIndex++)
 		{
 			std::string GenericPath = PathCompareString(OverlayContent.Paths[PathIndex]);
@@ -626,24 +640,36 @@ MergeChunkedFolderContents(const ChunkedFolderContent& Base, std::span<const Chu
 					{
 						RawHashToSequenceRawHashIndex.insert(
 							{RawHash, gsl::narrow<uint32_t>(Result.ChunkedContent.SequenceRawHashes.size())});
+
 						const uint32_t			  SequenceRawHashIndex = OverlayLookup.RawHashToSequenceIndex.at(RawHash);
 						const uint32_t			  OrderIndexOffset	   = OverlayLookup.SequenceIndexChunkOrderOffset[SequenceRawHashIndex];
 						const uint32_t			  ChunkCount		   = OverlayContent.ChunkedContent.ChunkCounts[SequenceRawHashIndex];
-						ChunkingStatistics		  Stats;
 						std::span<const uint32_t> OriginalChunkOrder =
 							std::span<const uint32_t>(OverlayContent.ChunkedContent.ChunkOrders).subspan(OrderIndexOffset, ChunkCount);
-						AddChunkSequence(Stats,
-										 Result.ChunkedContent,
-										 ChunkHashToChunkIndex,
-										 RawHash,
-										 OriginalChunkOrder,
-										 OverlayContent.ChunkedContent.ChunkHashes,
-										 OverlayContent.ChunkedContent.ChunkRawSizes);
+
+						SequencesToAdd.push_back(SequenceToAdd{.RawHash = RawHash, .OriginalChunkOrder = OriginalChunkOrder});
+
+						ChunkCountsAdded++;
+						ChunkOrdersAdded += OriginalChunkOrder.size();
+
 						Stats.UniqueSequencesFound++;
 					}
 				}
 			}
 		}
+
+		Result.ChunkedContent.ChunkCounts.reserve(Result.ChunkedContent.ChunkCounts.size() + ChunkCountsAdded);
+		Result.ChunkedContent.ChunkOrders.reserve(Result.ChunkedContent.ChunkOrders.size() + ChunkOrdersAdded);
+		for (SequenceToAdd& NewSequence : SequencesToAdd)
+		{
+			AddChunkSequence(Stats,
+							 Result.ChunkedContent,
+							 ChunkHashToChunkIndex,
+							 NewSequence.RawHash,
+							 NewSequence.OriginalChunkOrder,
+							 OverlayContent.ChunkedContent.ChunkHashes,
+							 OverlayContent.ChunkedContent.ChunkRawSizes);
+		}
 	};
 
 	tsl::robin_map<IoHash, uint32_t, IoHash::Hasher> MergedChunkHashToChunkIndex;
-- 
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