1. A database system comprising: a volatile memory device configured to include at least a portion to serve as a buffer cache, wherein the buffer cache is configured to implement a data retention policy, wherein the data retention policy is configured to overwrite least-recently used data in the buffer cache when new data is to be loaded into the buffer cache and size of the new data is greater than free space in the buffer cache; an array of persistent non-volatile storage devices configured to store data of a database, wherein the data of the database is loaded into the volatile memory device when accessed for use; a processor in communication with the array of persistent non-volatile storage devices and the volatile memory device; and a storage management module executable by the processor to: monitor a frequency of data value associated with a first portion of the data of the database stored in the buffer cache of the volatile memory; and store the first portion of data in the buffer cache of the volatile memory in response to the frequency of data value associated with the first portion of data being greater than a frequency of data value associated with at least a portion of the data of the database stored in the array of persistent non-volatile storage devices, wherein the first portion of data is available to read operations and write operations while stored in the buffer cache of the volatile memory; determine that other data stored in the array of persistent storage device is to be accessed for use; and override the data retention policy of the buffer cache to exclude the first portion of data from being overwritten by the other data stored while the first portion of data not actively being accessed for use, while the frequency of data value associated with the first portion of data remains greater than a frequency of data value associated with the at least a portion of the data of the database stored in the array of persistent non-volatile storage devices, the first portion of data is the least recently used data in the buffer cache and size of the other data is greater than free space in the buffer cache.