What is the definition of "due diligence" in the context of a search for a witness?

case law, " 'connotes persevering application, untiring efforts in good earnest, efforts of a substantial character.' " ' [Citation]. Considerations relevant to the due diligence inquiry 'include the timeliness of the search, the importance of the proffered testimony, and whether leads of the witness's possible location were competently explored.' [Citation.] In this regard, 'California law and federal constitutional requirements are the same. . . .' [Citation.]" (Id. at p. 622.) The prosecution shows due diligence where its "efforts are timely, reasonably extensive and carried out over a reasonable period." (People v. Bunyard (2009) 45 Cal.4th 836, 856.) In contrast, diligence is lacking where the prosecution's efforts to locate the witness "have been perfunctory or obviously negligent." (Id. at p. 855.)