 RDBs were used for these roles in most cases, although saving objects to a RDB can be complicated, a problem known as object-relational impedance mismatch.After , the need for high performance databases suitable for cloud computing and more closely matching the internal structure of the programs using them led to a renaissance in the key-value store market.These systems can store and retrieve associative arrays in a native fashion, which can greatly improve performance in common web-related workflows.