cautionary tale vs saga

cautionary tale

noun
  • A story, originally told in folklore, to warn its audience of a certain danger. 

saga

noun
  • Something with the qualities of such a saga; an epic, a long story. 

  • An Old Norse (Icelandic) prose narrative, especially one dealing with family or social histories and legends. 

How often have the words cautionary tale and saga occurred in a corpus of books? (source: Google Ngram Viewer )