A method comprising: maintaining, on persistent storage, a database that is accessible to a database server; wherein the database includes persistent-format data, stored in a persistent format; wherein a copy of all data items from the persistent-format data is stored on the persistent storage; converting at least a portion of the persistent-format data to a mirror format to produce mirror-format data; wherein the mirror format is different from and independent of the persistent format; maintaining the mirror-format data in volatile memory (102, 502, 504) accessible to the database server; wherein each data item in the mirror-format data is a copy of a corresponding data item in the persistent-format data; within the volatile memory (102, 502, 504), as the database server executes database operations that make changes to the persistent-format data, the database server maintaining the mirror-format data transactionally consistent with the persistent-format data in that any data items provided to a transaction from the mirror-format data will be the same version that would have been provided if the data items were provided to the transaction from the persistent-format data; determining, by the database server, that a scan operation of a table of the database which has at least a portion of its data in volatile memory (102, 502, 504) as mirror-format data is to be performed; in response to said determination, the database server performing a scan operation on the table in which a first set of data items for the scan operation are obtained from the mirror-format data and a second set of data items for the scan operation are obtained from the persistent-format data. maintaining, on persistent storage, a database that is accessible to a database server; wherein the database includes persistent-format data, stored in a persistent format; wherein a copy of all data items from the persistent-format data is stored on the persistent storage; converting at least a portion of the persistent-format data to a mirror format to produce mirror-format data; wherein the mirror format is different from and independent of the persistent format; maintaining the mirror-format data in volatile memory (102, 502, 504) accessible to the database server; wherein each data item in the mirror-format data is a copy of a corresponding data item in the persistent-format data; within the volatile memory (102, 502, 504), as the database server executes database operations that make changes to the persistent-format data, the database server maintaining the mirror-format data transactionally consistent with the persistent-format data in that any data items provided to a transaction from the mirror-format data will be the same version that would have been provided if the data items were provided to the transaction from the persistent-format data; determining, by the database server, that a scan operation of a table of the database which has at least a portion of its data in volatile memory (102, 502, 504) as mirror-format data is to be performed; in response to said determination, the database server performing a scan operation on the table in which a first set of data items for the scan operation are obtained from the mirror-format data and a second set of data items for the scan operation are obtained from the persistent-format data.