IEEE Transactions on Computers (TC), October 2015.
Youyou Lu*, Jiwu Shu*, Jia Guo*, Shuai Li*, Onur Mutlu
Carnegie Mellon University
* Tsinghua University
http://www.pdl.cmu.edu/
Flash memory has accelerated the architectural evolution of storage systems with its unique characteristics compared to magnetic disks. The no-overwrite property of flash memory naturally supports transactions, a commonly used mechanism in systems to provide consistency. However, existing embedded transaction designs in flash-based Solid State Drives (SSDs) either limit the transaction concurrency or introduce high overhead in tracking transaction states. This leads to low or unstable SSD performance. In this paper, we propose a transactional SSD (TxSSD) architecture, LightTx, to enable better concurrency and low overhead. First, LightTx improves transaction concurrency arbitrarily by using a page-independent commit protocol. Second, LightTx tracks the recent updates by leveraging the near-log-structured update property of SSDs and periodically retires dead transactions to reduce the transaction state tracking cost. Experiments show that LightTx achieves nearly the lowest overhead in garbage collection, memory consumption and mapping persistence compared to existing embedded transaction designs. LightTx also provides up to 20.6 percent performance improvement due to improved transaction concurrency.
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