Garbage collection for multi-version index on flash memory

In this paper, we study the important performance issues in using the purging-range query to reclaim old data versions to be free blocks in a flash-based multi-version database. To reduce the overheads for using the purging-range query in garbage collection, the physical block labeling (PBL) scheme is proposed to provide a better estimation on the purging version number to be used for purging old data versions. With the use of the frequency-based placement (FBP) scheme to place data versions in a block, the efficiency in garbage collection can be further enhanced by increasing the deadspans of data versions and reducing reallocation cost especially when the spaces of the flash memory for the databases are limited.