FlashKV: Accelerating KV Performance with Open-Channel SSDs

As the cost-per-bit of solid state disks is decreasing quickly, SSDs are supplanting HDDs in many cases, including the primary storage of key-value stores. However, simply deploying LSM-tree-based key-value stores on commercial SSDs is inefficient and induces heavy write amplification and severe garbage collection overhead under write-intensive conditions. The main cause of these critical issues comes from the triple redundant management functionalities lying in the LSM-tree, file system and flash translation layer, which block the awareness between key-value stores and flash devices. Furthermore, we observe that the performance of LSM-tree-based key-value stores is improved little by only eliminating these redundant layers, as the I/O stacks, including the cache and scheduler, are not optimized for LSM-tree’s unique I/O patterns.

To address the issues above, we propose FlashKV, an LSM-tree based key-value store running on open-channel SSDs. FlashKV eliminates the redundant management and semantic isolation by directly managing the raw flash devices in the application layer. With the domain knowledge of LSM-tree and the open-channel information, FlashKV employs a parallel data layout to exploit the internal parallelism of the flash device, and optimizes the compaction, caching and I/O scheduling mechanisms specifically. Evaluations show that FlashKV effectively improves system performance by 1.5× to 4.5× and decreases up to 50% write traffic under heavy write conditions, compared to LevelDB.