[HotStorage'22] Compaction-Aware Zone Allocation for LSM based Key-Value Store on ZNS SSDs

[HotStorage'22] Compaction-Aware Zone Allocation for LSM based Key-Value Store on ZNS SSDs

1. Motivations

• ZNS SSD
  • Space management is moved from device to host
  • Thus, application must perform zone cleaning
  • Write amplification: When cleaning a zone, if valid data remains, this data should be copied to other zone
  • To reduce WA, data with the same lifetime should be written in the same zone
• LIZA(LIfetime-based Zone Allocation) algorithm
  • Implemented in current ZenFS
  • How this algorithm predicts lifetime of data?
    • Same LSM level - same life time
      • However, LIZA fails by not accurately identifying lifetime
  • The two situations in which LIZA cannot avoid
    • SSTables have overlapping key ranges at adjacent levels of the LSM-tree can be placed in different zone
    • Compaction can invalidate SSTables across zones with different lifetime hint values.

2. CAZA(Compaction-Aware Zone Allocation) algorithm

• key point
  • A group of SSTables' lifetime is determined by the LSM-tree's compaction algoritm.
• Allocates a zone to SSTables that are newly created after merging SSTables with overlapping key ranges at ajacent level by considering how compaction input is selected in the LSM-tree

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