What database engine does Walmart use?

[SwissProgrammer]

If I wanted to write a game that could handle vast amounts of concurrent users, then it seems reasonable to look at how a large retailer handles information exchanges quickly. Thus, What database engine does Walmart use?

Thank you.

[SioSio]

Walmart uses DWH(Data Ware House) that stores more than 2.5 petabytes of data in SAP HANA.