ZNSKV: Reducing Data Migration in LSMT-Based KV Stores on ZNS SSDs

Zoned Namespace Solid State Drives (ZNS SSDs) delegate the data placement and garbage collection (GC) to the host It can provide predictable performance, and stable bandwidth for Log-Structured Merge Tree (LSMT) based key-value (KV) stores. We observe redundant data migration in GC and LSMT compaction, which exacerbates the write amplification (WA) of the KV store. In this paper, we propose our ZNS SSD based KV store ZNSKV to reduce the redundant data migration by two major components. First, we design the Compaction-GC scheme to reduce data migration by completing part of the GC in compaction. Second, the Compaction-GC scheme adjusts the file selection strategy according to the free capacity of storage devices, improving system performance while maintaining a high space utilization. Compared to mainstream LSMT-based KV stores with greedy GC, ZNSKV improves throughput by 32%, space utilization to 2.7 times, and lowers WA by 34% under write-intensive workloads.