diff --git a/core/src/cache/Cache.h b/core/src/cache/Cache.h
index 5f72fa5060a123260d9fd3f5fd80f5b2fc5c4225..34594c45739974cdb253742c8d54182e6f1ccda4 100644
--- a/core/src/cache/Cache.h
+++ b/core/src/cache/Cache.h
@@ -69,6 +69,9 @@ class Cache {
     void
     erase(const std::string& key);
 
+    bool
+    reserve(const int64_t size);
+
     void
     print();
 
@@ -77,7 +80,13 @@ class Cache {
 
  private:
     void
-    free_memory();
+    insert_internal(const std::string& key, const ItemObj& item);
+
+    void
+    erase_internal(const std::string& key);
+
+    void
+    free_memory_internal(const int64_t target_size);
 
  private:
     std::string header_;
diff --git a/core/src/cache/Cache.inl b/core/src/cache/Cache.inl
index 147c344532a29a2482fab4232c61da02af314012..607976e4117e16ee4df65a65ec163df78d0ed17f 100644
--- a/core/src/cache/Cache.inl
+++ b/core/src/cache/Cache.inl
@@ -13,8 +13,6 @@ namespace milvus {
 namespace cache {
 
 constexpr double DEFAULT_THRESHOLD_PERCENT = 0.7;
-constexpr double WARNING_THRESHOLD_PERCENT = 0.9;
-constexpr double BIG_ITEM_THRESHOLD_PERCENT = 0.1;
 
 template <typename ItemObj>
 Cache<ItemObj>::Cache(int64_t capacity, int64_t cache_max_count, const std::string& header)
@@ -28,9 +26,10 @@ Cache<ItemObj>::Cache(int64_t capacity, int64_t cache_max_count, const std::stri
 template <typename ItemObj>
 void
 Cache<ItemObj>::set_capacity(int64_t capacity) {
+    std::lock_guard<std::mutex> lock(mutex_);
     if (capacity > 0) {
         capacity_ = capacity;
-        free_memory();
+        free_memory_internal(capacity);
     }
 }
 
@@ -55,56 +54,95 @@ Cache<ItemObj>::get(const std::string& key) {
     if (!lru_.exists(key)) {
         return nullptr;
     }
-
     return lru_.get(key);
 }
 
 template <typename ItemObj>
 void
 Cache<ItemObj>::insert(const std::string& key, const ItemObj& item) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    insert_internal(key, item);
+}
+
+template <typename ItemObj>
+void
+Cache<ItemObj>::erase(const std::string& key) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    erase_internal(key);
+}
+
+template <typename ItemObj>
+bool
+Cache<ItemObj>::reserve(const int64_t item_size) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    if (item_size > capacity_) {
+        SERVER_LOG_ERROR << header_ << " item size " << (item_size >> 20) << "MB too big to insert into cache capacity"
+                         << (capacity_ >> 20) << "MB";
+        return false;
+    }
+    if (item_size > capacity_ - usage_) {
+        free_memory_internal(capacity_ - item_size);
+    }
+    return true;
+}
+
+template <typename ItemObj>
+void
+Cache<ItemObj>::clear() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    lru_.clear();
+    usage_ = 0;
+    SERVER_LOG_DEBUG << header_ << " Clear cache !";
+}
+
+
+template <typename ItemObj>
+void
+Cache<ItemObj>::print() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    size_t cache_count = lru_.size();
+    // for (auto it = lru_.begin(); it != lru_.end(); ++it) {
+    //     SERVER_LOG_DEBUG << it->first;
+    // }
+    SERVER_LOG_DEBUG << header_ << " [item count]: " << cache_count << ", [usage] " << (usage_ >> 20)
+                     << "MB, [capacity] " << (capacity_ >> 20) << "MB";
+}
+
+template <typename ItemObj>
+void
+Cache<ItemObj>::insert_internal(const std::string& key, const ItemObj& item) {
     if (item == nullptr) {
         return;
     }
 
     size_t item_size = item->Size();
-    // calculate usage
-    {
-        std::lock_guard<std::mutex> lock(mutex_);
-
-        // if key already exist, subtract old item size
-        if (lru_.exists(key)) {
-            const ItemObj& old_item = lru_.get(key);
-            usage_ -= old_item->Size();
-        }
-
-        // plus new item size
-        usage_ += item_size;
+
+    // if key already exist, subtract old item size
+    if (lru_.exists(key)) {
+        const ItemObj& old_item = lru_.get(key);
+        usage_ -= old_item->Size();
     }
 
+    // plus new item size
+    usage_ += item_size;
+
     // if usage exceed capacity, free some items
-    if (usage_ > capacity_ ||
-        (item_size > (int64_t)(capacity_ * BIG_ITEM_THRESHOLD_PERCENT) &&
-         usage_ > (int64_t)(capacity_ * WARNING_THRESHOLD_PERCENT))) {
+    if (usage_ > capacity_) {
         SERVER_LOG_DEBUG << header_ << " Current usage " << (usage_ >> 20) << "MB is too high for capacity "
                          << (capacity_ >> 20) << "MB, start free memory";
-        free_memory();
+        free_memory_internal(capacity_);
     }
 
     // insert new item
-    {
-        std::lock_guard<std::mutex> lock(mutex_);
-
-        lru_.put(key, item);
-        SERVER_LOG_DEBUG << header_ << " Insert " << key << " size: " << (item_size >> 20) << "MB into cache";
-        SERVER_LOG_DEBUG << header_ << " Count: " << lru_.size() << ", Usage: " << (usage_ >> 20) << "MB, Capacity: "
-                         << (capacity_ >> 20) << "MB";
-    }
+    lru_.put(key, item);
+    SERVER_LOG_DEBUG << header_ << " Insert " << key << " size: " << (item_size >> 20) << "MB into cache";
+    SERVER_LOG_DEBUG << header_ << " Count: " << lru_.size() << ", Usage: " << (usage_ >> 20) << "MB, Capacity: "
+                     << (capacity_ >> 20) << "MB";
 }
 
 template <typename ItemObj>
 void
-Cache<ItemObj>::erase(const std::string& key) {
-    std::lock_guard<std::mutex> lock(mutex_);
+Cache<ItemObj>::erase_internal(const std::string& key) {
     if (!lru_.exists(key)) {
         return;
     }
@@ -122,22 +160,9 @@ Cache<ItemObj>::erase(const std::string& key) {
 
 template <typename ItemObj>
 void
-Cache<ItemObj>::clear() {
-    std::lock_guard<std::mutex> lock(mutex_);
-    lru_.clear();
-    usage_ = 0;
-    SERVER_LOG_DEBUG << header_ << " Clear cache !";
-}
-
-/* free memory space when CACHE occupation exceed its capacity */
-template <typename ItemObj>
-void
-Cache<ItemObj>::free_memory() {
-    // if (usage_ <= capacity_)
-    //     return;
-
-    int64_t threshhold = capacity_ * freemem_percent_;
-    int64_t delta_size = usage_ - threshhold;
+Cache<ItemObj>::free_memory_internal(const int64_t target_size) {
+    int64_t threshold = std::min((int64_t)(capacity_ * freemem_percent_), target_size);
+    int64_t delta_size = usage_ - threshold;
     if (delta_size <= 0) {
         delta_size = 1;  // ensure at least one item erased
     }
@@ -145,44 +170,22 @@ Cache<ItemObj>::free_memory() {
     std::set<std::string> key_array;
     int64_t released_size = 0;
 
-    {
-        std::lock_guard<std::mutex> lock(mutex_);
+    auto it = lru_.rbegin();
+    while (it != lru_.rend() && released_size < delta_size) {
+        auto& key = it->first;
+        auto& obj_ptr = it->second;
 
-        auto it = lru_.rbegin();
-        while (it != lru_.rend() && released_size < delta_size) {
-            auto& key = it->first;
-            auto& obj_ptr = it->second;
-
-            key_array.emplace(key);
-            released_size += obj_ptr->Size();
-            ++it;
-        }
+        key_array.emplace(key);
+        released_size += obj_ptr->Size();
+        ++it;
     }
 
     SERVER_LOG_DEBUG << header_ << " To be released memory size: " << (released_size >> 20) << "MB";
 
     for (auto& key : key_array) {
-        erase(key);
+        erase_internal(key);
     }
 }
 
-template <typename ItemObj>
-void
-Cache<ItemObj>::print() {
-    size_t cache_count = 0;
-    {
-        std::lock_guard<std::mutex> lock(mutex_);
-        cache_count = lru_.size();
-#if 0
-        for (auto it = lru_.begin(); it != lru_.end(); ++it) {
-            SERVER_LOG_DEBUG << it->first;
-        }
-#endif
-    }
-
-    SERVER_LOG_DEBUG << header_ << " [item count]: " << cache_count << ", [usage] " << (usage_ >> 20)
-                     << "MB, [capacity] " << (capacity_ >> 20) << "MB";
-}
-
 }  // namespace cache
 }  // namespace milvus
diff --git a/core/src/cache/CacheMgr.h b/core/src/cache/CacheMgr.h
index 168c00b68eaeeaa059edb618afb5c267d677bf0f..c7ab9e26ab1d01faca63772d72de5155194f2902 100644
--- a/core/src/cache/CacheMgr.h
+++ b/core/src/cache/CacheMgr.h
@@ -39,6 +39,9 @@ class CacheMgr {
     virtual void
     EraseItem(const std::string& key);
 
+    virtual bool
+    Reserve(const int64_t size);
+
     virtual void
     PrintInfo();
 
@@ -54,14 +57,20 @@ class CacheMgr {
     void
     SetCapacity(int64_t capacity);
 
+    void
+    Lock();
+
+    void
+    Unlock();
+
  protected:
     CacheMgr();
 
     virtual ~CacheMgr();
 
  protected:
-    using CachePtr = std::shared_ptr<Cache<ItemObj>>;
-    CachePtr cache_;
+    std::shared_ptr<Cache<ItemObj>> cache_;
+    std::mutex mutex_;
 };
 
 }  // namespace cache
diff --git a/core/src/cache/CacheMgr.inl b/core/src/cache/CacheMgr.inl
index f3eb6dc42eeefbc9546142c0916fd76d1864bc04..606510c66cace9ac3de6e699a4db387182a1035f 100644
--- a/core/src/cache/CacheMgr.inl
+++ b/core/src/cache/CacheMgr.inl
@@ -27,7 +27,6 @@ CacheMgr<ItemObj>::ItemCount() const {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return 0;
     }
-
     return (uint64_t)(cache_->size());
 }
 
@@ -38,7 +37,6 @@ CacheMgr<ItemObj>::ItemExists(const std::string& key) {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return false;
     }
-
     return cache_->exists(key);
 }
 
@@ -60,7 +58,6 @@ CacheMgr<ItemObj>::InsertItem(const std::string& key, const ItemObj& data) {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return;
     }
-
     cache_->insert(key, data);
     server::Metrics::GetInstance().CacheAccessTotalIncrement();
 }
@@ -72,11 +69,20 @@ CacheMgr<ItemObj>::EraseItem(const std::string& key) {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return;
     }
-
     cache_->erase(key);
     server::Metrics::GetInstance().CacheAccessTotalIncrement();
 }
 
+template <typename ItemObj>
+bool
+CacheMgr<ItemObj>::Reserve(const int64_t size) {
+    if (cache_ == nullptr) {
+        SERVER_LOG_ERROR << "Cache doesn't exist";
+        return false;
+    }
+    return cache_->reserve(size);
+}
+
 template <typename ItemObj>
 void
 CacheMgr<ItemObj>::PrintInfo() {
@@ -84,7 +90,6 @@ CacheMgr<ItemObj>::PrintInfo() {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return;
     }
-
     cache_->print();
 }
 
@@ -95,7 +100,6 @@ CacheMgr<ItemObj>::ClearCache() {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return;
     }
-
     cache_->clear();
 }
 
@@ -106,7 +110,6 @@ CacheMgr<ItemObj>::CacheUsage() const {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return 0;
     }
-
     return cache_->usage();
 }
 
@@ -117,7 +120,6 @@ CacheMgr<ItemObj>::CacheCapacity() const {
         SERVER_LOG_ERROR << "Cache doesn't exist";
         return 0;
     }
-
     return cache_->capacity();
 }
 
@@ -131,5 +133,17 @@ CacheMgr<ItemObj>::SetCapacity(int64_t capacity) {
     cache_->set_capacity(capacity);
 }
 
+template <typename ItemObj>
+void
+CacheMgr<ItemObj>::Lock() {
+    mutex_.lock();
+}
+
+template <typename ItemObj>
+void
+CacheMgr<ItemObj>::Unlock() {
+    mutex_.unlock();
+}
+
 }  // namespace cache
 }  // namespace milvus
diff --git a/core/src/cache/GpuCacheMgr.cpp b/core/src/cache/GpuCacheMgr.cpp
index 374d141fc0da93dacd7851b0e220510496835045..30e4ec4c5a6241be854f8f191ae185dc54cfd971 100644
--- a/core/src/cache/GpuCacheMgr.cpp
+++ b/core/src/cache/GpuCacheMgr.cpp
@@ -22,7 +22,7 @@ namespace cache {
 
 #ifdef MILVUS_GPU_VERSION
 std::mutex GpuCacheMgr::global_mutex_;
-std::unordered_map<int64_t, std::pair<GpuCacheMgrPtr, MutexPtr>> GpuCacheMgr::instance_;
+std::unordered_map<int64_t, GpuCacheMgrPtr> GpuCacheMgr::instance_;
 
 namespace {
 constexpr int64_t G_BYTE = 1024 * 1024 * 1024;
@@ -65,33 +65,28 @@ GpuCacheMgr::InsertItem(const std::string& key, const milvus::cache::DataObjPtr&
     }
 }
 
-GpuCacheMgrPtr
-GpuCacheMgr::GetInstance(int64_t gpu_id) {
-    if (instance_.find(gpu_id) == instance_.end()) {
-        std::lock_guard<std::mutex> lock(global_mutex_);
-        if (instance_.find(gpu_id) == instance_.end()) {
-            instance_[gpu_id] = std::make_pair(std::make_shared<GpuCacheMgr>(gpu_id), std::make_shared<std::mutex>());
-        }
-    }
-    return instance_[gpu_id].first;
+bool
+GpuCacheMgr::Reserve(const int64_t size) {
+    return CacheMgr<DataObjPtr>::Reserve(size);
 }
 
-MutexPtr
-GpuCacheMgr::GetInstanceMutex(int64_t gpu_id) {
+GpuCacheMgrPtr
+GpuCacheMgr::GetInstance(int64_t gpu_id) {
     if (instance_.find(gpu_id) == instance_.end()) {
         std::lock_guard<std::mutex> lock(global_mutex_);
         if (instance_.find(gpu_id) == instance_.end()) {
-            instance_[gpu_id] = std::make_pair(std::make_shared<GpuCacheMgr>(gpu_id), std::make_shared<std::mutex>());
+            instance_[gpu_id] = std::make_shared<GpuCacheMgr>(gpu_id);
         }
     }
-    return instance_[gpu_id].second;
+    return instance_[gpu_id];
 }
 
 void
 GpuCacheMgr::OnGpuCacheCapacityChanged(int64_t capacity) {
     for (auto& iter : instance_) {
-        std::lock_guard<std::mutex> lock(*(iter.second.second));
-        iter.second.first->SetCapacity(capacity * G_BYTE);
+        iter.second->Lock();
+        iter.second->SetCapacity(capacity * G_BYTE);
+        iter.second->Unlock();
     }
 }
 
diff --git a/core/src/cache/GpuCacheMgr.h b/core/src/cache/GpuCacheMgr.h
index d96d6f3c89c142b4e5e59949ea9776448af4ce58..17a92c1d8e438dc2ce17f5f2cd7a33ed5b87933f 100644
--- a/core/src/cache/GpuCacheMgr.h
+++ b/core/src/cache/GpuCacheMgr.h
@@ -39,12 +39,12 @@ class GpuCacheMgr : public CacheMgr<DataObjPtr>, public server::GpuResourceConfi
     void
     InsertItem(const std::string& key, const DataObjPtr& data);
 
+    bool
+    Reserve(const int64_t size);
+
     static GpuCacheMgrPtr
     GetInstance(int64_t gpu_id);
 
-    static MutexPtr
-    GetInstanceMutex(int64_t gpu_id);
-
  protected:
     void
     OnGpuCacheCapacityChanged(int64_t capacity) override;
@@ -53,7 +53,7 @@ class GpuCacheMgr : public CacheMgr<DataObjPtr>, public server::GpuResourceConfi
     bool gpu_enable_ = true;
     int64_t gpu_id_;
     static std::mutex global_mutex_;
-    static std::unordered_map<int64_t, std::pair<GpuCacheMgrPtr, MutexPtr>> instance_;
+    static std::unordered_map<int64_t, GpuCacheMgrPtr> instance_;
     std::string identity_;
 };
 #endif
diff --git a/core/src/db/engine/ExecutionEngine.h b/core/src/db/engine/ExecutionEngine.h
index e7739d4d53bb49acbe113f454a90e4420cc4336e..d8911bd08fa4c08ddea18cf6e88b14077abbdcde 100644
--- a/core/src/db/engine/ExecutionEngine.h
+++ b/core/src/db/engine/ExecutionEngine.h
@@ -111,9 +111,6 @@ class ExecutionEngine {
     virtual Status
     Cache() = 0;
 
-    virtual Status
-    GpuCache(uint64_t gpu_id) = 0;
-
     virtual Status
     Init() = 0;
 
diff --git a/core/src/db/engine/ExecutionEngineImpl.cpp b/core/src/db/engine/ExecutionEngineImpl.cpp
index dbbee791b6ebaaa173cddd3fced31f27737d959f..ace870226c69271b8f741bedf4de2bb04c284bed 100644
--- a/core/src/db/engine/ExecutionEngineImpl.cpp
+++ b/core/src/db/engine/ExecutionEngineImpl.cpp
@@ -41,6 +41,7 @@
 #include "metrics/Metrics.h"
 #include "scheduler/Utils.h"
 #include "utils/CommonUtil.h"
+#include "utils/Error.h"
 #include "utils/Exception.h"
 #include "utils/Log.h"
 #include "utils/Status.h"
@@ -545,13 +546,16 @@ ExecutionEngineImpl::CopyToGpu(uint64_t device_id, bool hybrid) {
 
         try {
             /* Index data is copied to GPU first, then added into GPU cache.
-             * We MUST add a lock here to avoid more than one INDEX are copied to one GPU card at same time,
-             * which will potentially cause GPU out of memory.
+             * Add lock here to avoid multiple INDEX are copied to one GPU card at same time.
+             * And reserve space to avoid GPU out of memory issue.
              */
-            std::lock_guard<std::mutex> lock(*(cache::GpuCacheMgr::GetInstanceMutex(device_id)));
             ENGINE_LOG_DEBUG << "CPU to GPU" << device_id << " start";
+            auto gpu_cache_mgr = cache::GpuCacheMgr::GetInstance(device_id);
+            gpu_cache_mgr->Lock();
+            gpu_cache_mgr->Reserve(index_->Size());
             index_ = knowhere::cloner::CopyCpuToGpu(index_, device_id, knowhere::Config());
-            GpuCache(device_id);
+            gpu_cache_mgr->InsertItem(location_, std::static_pointer_cast<cache::DataObj>(index_));
+            gpu_cache_mgr->Unlock();
             ENGINE_LOG_DEBUG << "CPU to GPU" << device_id << " finished";
         } catch (std::exception& e) {
             ENGINE_LOG_ERROR << e.what();
@@ -568,10 +572,11 @@ ExecutionEngineImpl::CopyToIndexFileToGpu(uint64_t device_id) {
 #ifdef MILVUS_GPU_VERSION
     // the ToIndexData is only a placeholder, cpu-copy-to-gpu action is performed in
     if (index_) {
+        auto gpu_cache_mgr = milvus::cache::GpuCacheMgr::GetInstance(device_id);
+        gpu_cache_mgr->Lock();
         gpu_num_ = device_id;
-        auto to_index_data = std::make_shared<knowhere::ToIndexData>(index_->Size());
-        cache::DataObjPtr obj = std::static_pointer_cast<cache::DataObj>(to_index_data);
-        milvus::cache::GpuCacheMgr::GetInstance(device_id)->InsertItem(location_ + "_placeholder", obj);
+        gpu_cache_mgr->Reserve(index_->Size());
+        gpu_cache_mgr->Unlock();
     }
 #endif
     return Status::OK();
@@ -954,18 +959,11 @@ ExecutionEngineImpl::GetVectorByID(const int64_t& id, uint8_t* vector, bool hybr
 
 Status
 ExecutionEngineImpl::Cache() {
+    auto cpu_cache_mgr = milvus::cache::CpuCacheMgr::GetInstance();
+    cpu_cache_mgr->Lock();
     cache::DataObjPtr obj = std::static_pointer_cast<cache::DataObj>(index_);
-    milvus::cache::CpuCacheMgr::GetInstance()->InsertItem(location_, obj);
-
-    return Status::OK();
-}
-
-Status
-ExecutionEngineImpl::GpuCache(uint64_t gpu_id) {
-#ifdef MILVUS_GPU_VERSION
-    cache::DataObjPtr obj = std::static_pointer_cast<cache::DataObj>(index_);
-    milvus::cache::GpuCacheMgr::GetInstance(gpu_id)->InsertItem(location_, obj);
-#endif
+    cpu_cache_mgr->InsertItem(location_, obj);
+    cpu_cache_mgr->Unlock();
     return Status::OK();
 }
 
diff --git a/core/src/db/engine/ExecutionEngineImpl.h b/core/src/db/engine/ExecutionEngineImpl.h
index d8ef30a6aa8482ebe320838155b0e2d551d574a2..35e0b9c217e6a16106b11fd862af9e48bb2e0b0f 100644
--- a/core/src/db/engine/ExecutionEngineImpl.h
+++ b/core/src/db/engine/ExecutionEngineImpl.h
@@ -86,9 +86,6 @@ class ExecutionEngineImpl : public ExecutionEngine {
     Status
     Cache() override;
 
-    Status
-    GpuCache(uint64_t gpu_id) override;
-
     Status
     Init() override;
 
diff --git a/core/unittest/db/test_engine.cpp b/core/unittest/db/test_engine.cpp
index ac05c4d1e137ef1f80971182cededa2f0ccbf15f..aac6fcd8b38bf304eaf1ea314121710b2973b40b 100644
--- a/core/unittest/db/test_engine.cpp
+++ b/core/unittest/db/test_engine.cpp
@@ -203,8 +203,6 @@ TEST_F(EngineTest, ENGINE_IMPL_TEST) {
 
         auto status = engine_ptr->CopyToGpu(0, false);
         ASSERT_TRUE(status.ok());
-        status = engine_ptr->GpuCache(0);
-        ASSERT_TRUE(status.ok());
         status = engine_ptr->CopyToGpu(0, false);
         ASSERT_TRUE(status.ok());