Add IDatabaseTablesIterator::reset() interface

src/Databases/DatabaseLazy.cpp

@@ -329,4 +329,10 @@ const StoragePtr & DatabaseLazyIterator::table() const
     return current_storage;
 }
 
+void DatabaseLazyIterator::reset()
+{
+    if (current_storage)
+        current_storage.reset();
+}
+
 }

src/Databases/DatabaseLazy.h

@@ -122,6 +122,7 @@ public:
     bool isValid() const override;
     const String & name() const override;
     const StoragePtr & table() const override;
+    void reset() override;
 
 private:
     const DatabaseLazy & database;

src/Databases/IDatabase.h

@@ -44,6 +44,8 @@ public:
     /// (a database with support for lazy tables loading
     /// - it maintains a list of tables but tables are loaded lazily).
     virtual const StoragePtr & table() const = 0;
+    /// Reset reference counter to the StoragePtr.
+    virtual void reset() = 0;
 
     virtual ~IDatabaseTablesIterator() = default;
 
@@ -93,6 +95,8 @@ public:
     const String & name() const override { return it->first; }
 
     const StoragePtr & table() const override { return it->second; }
+
+    void reset() override { it->second.reset(); }
 };
 
 /// Copies list of dictionaries and iterates through such snapshot.

src/Databases/MySQL/DatabaseMaterializeTablesIterator.h

@@ -28,6 +28,11 @@ public:
         return tables.emplace_back(storage);
     }
 
+    void reset() override
+    {
+        tables.clear();
+    }
+
     UUID uuid() const override { return nested_iterator->uuid(); }
 
     DatabaseMaterializeTablesIterator(DatabaseTablesIteratorPtr nested_iterator_, DatabaseMaterializeMySQL * database_)