presto-memory-context/src/main/java/io/prestosql/memory/context/MemoryTrackingContext.java/MemoryTrackingContext/newUserMemoryContext
class MemoryTrackingContext:    public LocalMemoryContext newUserMemoryContext(String allocationTag)
    {
        return userAggregateMemoryContext.newLocalMemoryContext(allocationTag);
    }