diff --git a/AnnService/inc/Core/SPANN/Options.h b/AnnService/inc/Core/SPANN/Options.h
index f49621230..fb7c56a3f 100644
--- a/AnnService/inc/Core/SPANN/Options.h
+++ b/AnnService/inc/Core/SPANN/Options.h
@@ -23,6 +23,7 @@ namespace SPTAG {
             VectorFileType m_vectorType;
             SizeType m_vectorSize; //Optional on condition
             std::string m_vectorDelimiter; //Optional on condition
+            bool m_mmapVectors; // memory-map the input vector file instead of loading it fully into RAM
             std::string m_queryPath;
             VectorFileType m_queryType;
             SizeType m_querySize; //Optional on condition
diff --git a/AnnService/inc/Core/SPANN/ParameterDefinitionList.h b/AnnService/inc/Core/SPANN/ParameterDefinitionList.h
index 0a88e3f1d..690f7930e 100644
--- a/AnnService/inc/Core/SPANN/ParameterDefinitionList.h
+++ b/AnnService/inc/Core/SPANN/ParameterDefinitionList.h
@@ -12,6 +12,7 @@ DefineBasicParameter(m_vectorPath, std::string, std::string(""), "VectorPath")
 DefineBasicParameter(m_vectorType, SPTAG::VectorFileType, SPTAG::VectorFileType::DEFAULT, "VectorType")
 DefineBasicParameter(m_vectorSize, SPTAG::SizeType, -1, "VectorSize")
 DefineBasicParameter(m_vectorDelimiter, std::string, std::string("|"), "VectorDelimiter")
+DefineBasicParameter(m_mmapVectors, bool, false, "MmapVectors")
 DefineBasicParameter(m_queryPath, std::string, std::string(""), "QueryPath")
 DefineBasicParameter(m_queryType, SPTAG::VectorFileType, SPTAG::VectorFileType::Undefined, "QueryType")
 DefineBasicParameter(m_querySize, SPTAG::SizeType, -1, "QuerySize")
diff --git a/AnnService/inc/Helper/ConcurrentSet.h b/AnnService/inc/Helper/ConcurrentSet.h
index 49210a29e..9c9f534f5 100644
--- a/AnnService/inc/Helper/ConcurrentSet.h
+++ b/AnnService/inc/Helper/ConcurrentSet.h
@@ -16,6 +16,7 @@
 #include <unordered_set>
 #include <unordered_map>
 #include <queue>
+#include <deque>
 #endif // TBB
 #else
 #include <concurrent_unordered_map.h>
@@ -47,9 +48,10 @@ namespace SPTAG
             template <typename T>
             class ConcurrentSet
             {
+            public:
                 typedef typename std::unordered_set<T>::iterator iterator;
+                typedef typename std::unordered_set<T>::const_iterator const_iterator;
 
-            public:
                 ConcurrentSet() { m_lock.reset(new std::shared_timed_mutex); }
 
                 ~ConcurrentSet() {}
@@ -72,6 +74,14 @@ namespace SPTAG
                     return m_data.insert(key);
                 }
 
+                // Unsafe iteration: caller must ensure no concurrent modification.
+                // Mirrors the semantics of tbb::concurrent_unordered_set::unsafe_begin/unsafe_end,
+                // which (unlike the locked accessors above) do not synchronize.
+                iterator begin() { return m_data.begin(); }
+                iterator end() { return m_data.end(); }
+                const_iterator begin() const { return m_data.begin(); }
+                const_iterator end() const { return m_data.end(); }
+
             private:
                 std::unique_ptr<std::shared_timed_mutex> m_lock;
                 std::unordered_set<T> m_data;
@@ -80,9 +90,10 @@ namespace SPTAG
             template <typename K, typename V>
             class ConcurrentMap
             {
+            public:
                 typedef typename std::unordered_map<K, V>::iterator iterator;
+                typedef typename std::unordered_map<K, V>::value_type value_type;
 
-            public:
                 ConcurrentMap(int capacity = 8) { m_lock.reset(new std::shared_timed_mutex); m_data.reserve(capacity); }
 
                 ~ConcurrentMap() {}
@@ -127,6 +138,8 @@ namespace SPTAG
             class ConcurrentQueue
             {
             public:
+                typedef typename std::deque<T>::iterator iterator;
+                typedef typename std::deque<T>::const_iterator const_iterator;
 
                 ConcurrentQueue() {}
 
@@ -135,7 +148,7 @@ namespace SPTAG
                 void push(const T& j)
                 {
                     std::lock_guard<std::mutex> lock(m_lock);
-                    m_queue.push(j);
+                    m_queue.push_back(j);
                 }
 
                 bool try_pop(T& j)
@@ -145,13 +158,36 @@ namespace SPTAG
                         return false;
                     }
                     j = m_queue.front();
-                    m_queue.pop();
+                    m_queue.pop_front();
                     return true;
                 }
 
+                // The TBB concurrent_queue exposes empty() and unsafe_size() as
+                // best-effort, lock-free queries. Here we take the lock so the
+                // snapshot is consistent; callers should still treat the result
+                // as advisory in concurrent contexts.
+                bool empty() const
+                {
+                    std::lock_guard<std::mutex> lock(m_lock);
+                    return m_queue.empty();
+                }
+
+                size_t unsafe_size() const
+                {
+                    std::lock_guard<std::mutex> lock(m_lock);
+                    return m_queue.size();
+                }
+
+                // Unsafe iteration: caller must ensure no concurrent modification,
+                // matching tbb::concurrent_queue::unsafe_begin/unsafe_end semantics.
+                iterator unsafe_begin() { return m_queue.begin(); }
+                iterator unsafe_end() { return m_queue.end(); }
+                const_iterator unsafe_begin() const { return m_queue.begin(); }
+                const_iterator unsafe_end() const { return m_queue.end(); }
+
             protected:
-                std::mutex m_lock;
-                std::queue<T> m_queue;
+                mutable std::mutex m_lock;
+                std::deque<T> m_queue;
             };
 
             template <typename T>
@@ -161,7 +197,7 @@ namespace SPTAG
                 ConcurrentPriorityQueue() {}
                 ~ConcurrentPriorityQueue() {}
 
-            size_type size() const {
+            size_t size() const {
                 std::lock_guard<std::mutex> lock(m_lock);
                 return m_queue.size();
             }
@@ -178,11 +214,11 @@ namespace SPTAG
                 }
                 value = m_queue.top();
                 m_queue.pop();
-                return true; 
+                return true;
             }
 
             private:
-                std::mutex m_lock;
+                mutable std::mutex m_lock;
                 std::priority_queue<T> m_queue;
             };
 #endif // TBB
diff --git a/AnnService/inc/Helper/Logging.h b/AnnService/inc/Helper/Logging.h
index 221f4dfa5..d5e379481 100644
--- a/AnnService/inc/Helper/Logging.h
+++ b/AnnService/inc/Helper/Logging.h
@@ -37,7 +37,14 @@ namespace SPTAG
 
         class LoggerHolder
         {
-#if ((defined(_MSVC_LANG) && _MSVC_LANG >= 	202002L) || __cplusplus >= 	202002L)
+        // The C++20 path uses `std::atomic<std::shared_ptr<Logger>>`, which the
+        // libc++ shipped with ClickHouse rejects (it requires the value type to
+        // be trivially copyable). The pre-C++20 path with `std::atomic_load` /
+        // `std::atomic_store` works under both standards, so force it
+        // unconditionally — same workaround SPTAG-cmake uses for `_sptag` via
+        // `-std=c++17`, but applied at the header so consumers compiled at
+        // higher standards (e.g. ClickHouse's `dbms` at C++23) are unaffected.
+#if 0
         private:
             std::atomic<std::shared_ptr<Logger>> m_logger;
         public:
diff --git a/AnnService/inc/Helper/MemoryMappedFile.h b/AnnService/inc/Helper/MemoryMappedFile.h
new file mode 100644
index 000000000..a61b07fc3
--- /dev/null
+++ b/AnnService/inc/Helper/MemoryMappedFile.h
@@ -0,0 +1,140 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+#ifndef _SPTAG_HELPER_MEMORYMAPPEDFILE_H_
+#define _SPTAG_HELPER_MEMORYMAPPEDFILE_H_
+
+#include <cstdint>
+#include <string>
+
+#ifdef _MSC_VER
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN
+#endif
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <windows.h>
+#else
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#endif
+
+namespace SPTAG
+{
+namespace Helper
+{
+
+// RAII read-only whole-file memory mapping. The OS demand-pages the file on access and
+// reclaims clean file-backed pages under memory pressure, so resident set stays bounded
+// instead of holding the whole file in heap. Header-only so it needs no build-list change.
+class MemoryMappedFile
+{
+public:
+    MemoryMappedFile() = default;
+
+    ~MemoryMappedFile() { Close(); }
+
+    // Non-copyable, non-movable: a single owner unmaps exactly once.
+    MemoryMappedFile(const MemoryMappedFile&) = delete;
+    MemoryMappedFile& operator=(const MemoryMappedFile&) = delete;
+
+    // Maps the entire file read-only. Returns false (and leaves the object closed) on failure.
+    bool Open(const std::string& p_path)
+    {
+        Close();
+#ifdef _MSC_VER
+        HANDLE file = ::CreateFileA(p_path.c_str(), GENERIC_READ, FILE_SHARE_READ, nullptr,
+                                    OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, nullptr);
+        if (file == INVALID_HANDLE_VALUE) return false;
+
+        LARGE_INTEGER size;
+        if (!::GetFileSizeEx(file, &size) || size.QuadPart <= 0)
+        {
+            ::CloseHandle(file);
+            return false;
+        }
+
+        HANDLE mapping = ::CreateFileMappingA(file, nullptr, PAGE_READONLY, 0, 0, nullptr);
+        if (mapping == nullptr)
+        {
+            ::CloseHandle(file);
+            return false;
+        }
+
+        void* view = ::MapViewOfFile(mapping, FILE_MAP_READ, 0, 0, 0);
+        if (view == nullptr)
+        {
+            ::CloseHandle(mapping);
+            ::CloseHandle(file);
+            return false;
+        }
+
+        m_base = reinterpret_cast<std::uint8_t*>(view);
+        m_length = static_cast<std::uint64_t>(size.QuadPart);
+        m_file = file;
+        m_mapping = mapping;
+        return true;
+#else
+        int fd = ::open(p_path.c_str(), O_RDONLY);
+        if (fd < 0) return false;
+
+        struct stat st;
+        if (::fstat(fd, &st) != 0 || st.st_size <= 0)
+        {
+            ::close(fd);
+            return false;
+        }
+
+        void* p = ::mmap(nullptr, static_cast<size_t>(st.st_size), PROT_READ, MAP_SHARED, fd, 0);
+        // The mapping keeps its own reference to the file, so the descriptor can be closed now.
+        ::close(fd);
+        if (p == MAP_FAILED) return false;
+
+#if defined(MADV_RANDOM)
+        // BKT build accesses vectors randomly by id; suppress readahead to keep RSS tight.
+        ::madvise(p, static_cast<size_t>(st.st_size), MADV_RANDOM);
+#endif
+        m_base = reinterpret_cast<std::uint8_t*>(p);
+        m_length = static_cast<std::uint64_t>(st.st_size);
+        return true;
+#endif
+    }
+
+    void Close()
+    {
+        if (m_base == nullptr) return;
+#ifdef _MSC_VER
+        ::UnmapViewOfFile(m_base);
+        if (m_mapping != nullptr) ::CloseHandle(m_mapping);
+        if (m_file != nullptr) ::CloseHandle(m_file);
+        m_mapping = nullptr;
+        m_file = nullptr;
+#else
+        ::munmap(m_base, static_cast<size_t>(m_length));
+#endif
+        m_base = nullptr;
+        m_length = 0;
+    }
+
+    const std::uint8_t* Data() const { return m_base; }
+
+    std::uint64_t Length() const { return m_length; }
+
+    bool IsOpen() const { return m_base != nullptr; }
+
+private:
+    std::uint8_t* m_base = nullptr;
+    std::uint64_t m_length = 0;
+#ifdef _MSC_VER
+    void* m_file = nullptr;
+    void* m_mapping = nullptr;
+#endif
+};
+
+} // namespace Helper
+} // namespace SPTAG
+
+#endif // _SPTAG_HELPER_MEMORYMAPPEDFILE_H_
diff --git a/AnnService/inc/Helper/VectorSetReader.h b/AnnService/inc/Helper/VectorSetReader.h
index ea68419dc..c65537e95 100644
--- a/AnnService/inc/Helper/VectorSetReader.h
+++ b/AnnService/inc/Helper/VectorSetReader.h
@@ -34,6 +34,10 @@ class ReaderOptions : public ArgumentsParser
     std::uint32_t m_threadNum;
 
     bool m_normalized;
+
+    // When true (and the file type supports it), map the input vector file instead of
+    // reading it fully into RAM, so the OS demand-pages it and RSS stays bounded.
+    bool m_useMmap = false;
 };
 
 class VectorSetReader
diff --git a/AnnService/src/Core/SPANN/SPANNIndex.cpp b/AnnService/src/Core/SPANN/SPANNIndex.cpp
index 0c34a17b8..9d95fe202 100644
--- a/AnnService/src/Core/SPANN/SPANNIndex.cpp
+++ b/AnnService/src/Core/SPANN/SPANNIndex.cpp
@@ -1246,6 +1246,16 @@ template <typename T> ErrorCode Index<T>::BuildIndex(bool p_normalized)
     std::shared_ptr<Helper::ReaderOptions> vectorOptions(
         new Helper::ReaderOptions(valueType, dim, m_options.m_vectorType, m_options.m_vectorDelimiter,
                                   m_options.m_iSSDNumberOfThreads, p_normalized));
+    // A read-only mapping cannot satisfy the in-place Normalize done in SelectHead, so mmap is
+    // only enabled when no normalization is required (L2, or already-normalized Cosine input).
+    bool needNormalize = (m_options.m_distCalcMethod == DistCalcMethod::Cosine) && !p_normalized;
+    vectorOptions->m_useMmap = m_options.m_mmapVectors && !needNormalize;
+    if (m_options.m_mmapVectors && needNormalize)
+    {
+        SPTAGLIB_LOG(Helper::LogLevel::LL_Warning,
+                     "MmapVectors disabled: Cosine with un-normalized input requires in-place "
+                     "Normalize; using in-memory load. Pre-normalize input or use L2 to enable mmap.\n");
+    }
     auto vectorReader = Helper::VectorSetReader::CreateInstance(vectorOptions);
     if (m_options.m_vectorPath.empty())
     {
diff --git a/AnnService/src/Core/VectorIndex.cpp b/AnnService/src/Core/VectorIndex.cpp
index 2f8ebfd13..5b7bd5270 100644
--- a/AnnService/src/Core/VectorIndex.cpp
+++ b/AnnService/src/Core/VectorIndex.cpp
@@ -1185,7 +1185,7 @@ void VectorIndex::ApproximateRNG(std::shared_ptr<VectorSet> &fullVectors, std::u
                     default:
                         SPTAGLIB_LOG(
                             Helper::LogLevel::LL_Error, "Unable to get quantizer reconstruct type %s",
-                            Helper::Convert::ConvertToString<VectorValueType>(m_pQuantizer->GetReconstructType()));
+                            Helper::Convert::ConvertToString<VectorValueType>(m_pQuantizer->GetReconstructType()).c_str());
                     }
                 }
                 else
diff --git a/AnnService/src/Helper/VectorSetReaders/DefaultReader.cpp b/AnnService/src/Helper/VectorSetReaders/DefaultReader.cpp
index eeb89a5a2..9bfa9c61a 100644
--- a/AnnService/src/Helper/VectorSetReaders/DefaultReader.cpp
+++ b/AnnService/src/Helper/VectorSetReaders/DefaultReader.cpp
@@ -4,6 +4,7 @@
 #include "inc/Helper/VectorSetReaders/DefaultReader.h"
 #include "inc/Core/VectorIndex.h"
 #include "inc/Helper/CommonHelper.h"
+#include "inc/Helper/MemoryMappedFile.h"
 
 using namespace SPTAG;
 using namespace SPTAG::Helper;
@@ -33,6 +34,40 @@ ErrorCode DefaultVectorReader::LoadFile(const std::string &p_filePaths)
 
 std::shared_ptr<VectorSet> DefaultVectorReader::GetVectorSet(SizeType start, SizeType end) const
 {
+    if (m_options->m_useMmap)
+    {
+        auto mmf = std::make_shared<Helper::MemoryMappedFile>();
+        if (mmf->Open(m_vectorOutput) &&
+            mmf->Length() >= (std::uint64_t)(sizeof(SizeType) + sizeof(DimensionType)))
+        {
+            const std::uint8_t *base = mmf->Data();
+            SizeType row = *reinterpret_cast<const SizeType *>(base);
+            DimensionType col = *reinterpret_cast<const DimensionType *>(base + sizeof(SizeType));
+
+            if (start > row)
+                start = row;
+            if (end < 0 || end > row)
+                end = row;
+
+            std::uint64_t perVec = ((std::uint64_t)GetValueTypeSize(m_options->m_inputValueType)) * col;
+            std::uint64_t dataOffset = sizeof(SizeType) + sizeof(DimensionType) + ((std::uint64_t)start) * perVec;
+            std::uint64_t dataLen = ((std::uint64_t)(end - start)) * perVec;
+
+            if (dataOffset + dataLen <= mmf->Length())
+            {
+                std::uint8_t *dataPtr = const_cast<std::uint8_t *>(base) + dataOffset;
+                // Aliasing shared_ptr: shares ownership with mmf (so the mapping outlives every
+                // copy of the ByteArray / BasicVectorSet) but get() returns the data pointer.
+                std::shared_ptr<std::uint8_t> holder(mmf, dataPtr);
+                ByteArray vectorSet(dataPtr, dataLen, holder);
+                SPTAGLIB_LOG(Helper::LogLevel::LL_Info, "Mmap Vector(%d,%d)\n", end - start, col);
+                return std::make_shared<BasicVectorSet>(vectorSet, m_options->m_inputValueType, col, end - start);
+            }
+        }
+        SPTAGLIB_LOG(Helper::LogLevel::LL_Warning,
+                     "mmap failed for %s, falling back to in-memory read.\n", m_vectorOutput.c_str());
+    }
+
     auto ptr = f_createIO();
     if (ptr == nullptr || !ptr->Initialize(m_vectorOutput.c_str(), std::ios::binary | std::ios::in))
     {
diff --git a/AnnService/src/Helper/VectorSetReaders/TxtReader.cpp b/AnnService/src/Helper/VectorSetReaders/TxtReader.cpp
index 8bf9fb55c..ef1439821 100644
--- a/AnnService/src/Helper/VectorSetReaders/TxtReader.cpp
+++ b/AnnService/src/Helper/VectorSetReaders/TxtReader.cpp
@@ -5,7 +5,9 @@
 #include "inc/Core/VectorIndex.h"
 #include "inc/Helper/CommonHelper.h"
 #include "inc/Helper/StringConvert.h"
-#include <omp.h>
+// <omp.h> was included historically but no OpenMP primitives are actually used
+// in this translation unit. Drop it — ClickHouse's contrib build does not
+// configure an OpenMP runtime.
 
 using namespace SPTAG;
 using namespace SPTAG::Helper;