modificate name to id data structure in Snapshots (#4483)

Signed-off-by: NXuPeng-SH <xupeng3112@163.com>

core/src/db/snapshot/Snapshots.cpp

@@ -55,7 +55,12 @@ Snapshots::DoDropCollection(ScopedSnapshotT& ss, const LSN_TYPE& lsn) {
     {
         std::unique_lock<std::shared_timed_mutex> lock(mutex_);
         alive_cids_.erase(context.collection->GetID());
-        name_id_map_.erase(context.collection->GetName());
+        auto& ids = name_id_map_[context.collection->GetName()];
+        if (ids.size() == 1) {
+            name_id_map_.erase(context.collection->GetName());
+        } else {
+            ids.erase(context.collection->GetID());
+        }
         /* holders_.erase(context.collection->GetID()); */
         auto h = holders_.find(context.collection->GetID());
         if (h != holders_.end()) {
@@ -133,8 +138,8 @@ Snapshots::GetCollectionIds(IDS_TYPE& ids) const {
 Status
 Snapshots::GetCollectionNames(std::vector<std::string>& names) const {
     std::shared_lock<std::shared_timed_mutex> lock(mutex_);
-    for (auto& kv : name_id_map_) {
-        names.push_back(kv.first);
+    for (auto& [name, _] : name_id_map_) {
+        names.push_back(name);
     }
     return Status::OK();
 }
@@ -180,8 +185,9 @@ Snapshots::GetHolder(const std::string& name, SnapshotHolderPtr& holder) const {
     std::shared_lock<std::shared_timed_mutex> lock(mutex_);
     auto kv = name_id_map_.find(name);
     if (kv != name_id_map_.end()) {
+        auto id = *(kv->second.rbegin());
         lock.unlock();
-        return GetHolder(kv->second, holder);
+        return GetHolder(id, holder);
     }
     std::stringstream emsg;
     emsg << "Snapshots::GetHolderNoLock: Specified snapshot holder for collection ";
@@ -215,7 +221,12 @@ Snapshots::LoadHolder(StorePtr store, const ID_TYPE& collection_id, SnapshotHold
     holders_[collection_id] = holder;
     ScopedSnapshotT ss;
     STATUS_CHECK(holder->Load(store, ss));
-    name_id_map_[ss->GetName()] = collection_id;
+    auto it = name_id_map_.find(ss->GetName());
+    if (it == name_id_map_.end()) {
+        name_id_map_[ss->GetName()] = {collection_id};
+    } else {
+        name_id_map_[ss->GetName()].insert(collection_id);
+    }
     alive_cids_.insert(collection_id);
     return Status::OK();
 }
@@ -284,14 +295,14 @@ Snapshots::OnReaderTimer(const boost::system::error_code& ec) {
     }
     auto aids = op2->GetIDs();
 
-    std::set<ID_TYPE> diff;
+    std::set<ID_TYPE> stale_ids;
     {
         std::unique_lock<std::shared_timed_mutex> lock(mutex_);
         std::set_difference(alive_cids_.begin(), alive_cids_.end(), aids.begin(), aids.end(),
-                            std::inserter(diff, diff.begin()));
+                            std::inserter(stale_ids, stale_ids.begin()));
     }
 
-    for (auto& cid : diff) {
+    for (auto& cid : stale_ids) {
         ScopedSnapshotT ss;
         status = GetSnapshot(ss, cid);
         if (!status.ok()) {
@@ -300,7 +311,12 @@ Snapshots::OnReaderTimer(const boost::system::error_code& ec) {
         }
         std::unique_lock<std::shared_timed_mutex> lock(mutex_);
         alive_cids_.erase(cid);
-        name_id_map_.erase(ss->GetName());
+        auto& ids = name_id_map_[ss->GetName()];
+        if (ids.size() == 1) {
+            name_id_map_.erase(ss->GetName());
+        } else {
+            ids.erase(ss->GetID());
+        }
         holders_.erase(cid);
     }
 }

core/src/db/snapshot/Snapshots.h

@@ -100,7 +100,7 @@ class Snapshots {
     mutable std::shared_timed_mutex mutex_;
     std::map<ID_TYPE, SnapshotHolderPtr> holders_;
     std::set<ID_TYPE> alive_cids_;
-    std::map<std::string, ID_TYPE> name_id_map_;
+    std::map<std::string, std::set<ID_TYPE>> name_id_map_;
     mutable std::shared_timed_mutex inactive_mtx_;
     std::map<ID_TYPE, SnapshotHolderPtr> inactive_holders_;
     std::set<ID_TYPE> invalid_ssid_;