KVS Tree Stream Selection for SSD Write Amplification
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Solution Overview
Problem
LSM trees face issues such as high write amplification, inefficient search performance, and limited write throughput due to their constant merging and sorted nature, leading to increased wear on SSDs and resource consumption.
Innovation Solution
The KVS tree employs temporally ordered sequences of immutable key-value sets with determinative mapping and bloom filters, separating keys and values, and using a radix-based key distribution method to reduce write amplification and improve search efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LSM trees use constant merging and sorted structure, then search performance is improved, but write amplification increases and write throughput decreases
Solution Approach 1:
The patent segments the LSM tree into multiple independent streams (first stream for hot data, second stream for cold data), allowing different parts of the data to be managed separately. This enables selective merging operations that reduce unnecessary writes while maintaining efficient search performance for both hot and cold data access patterns
Solution Approach 2:
The patent applies different quality characteristics to different parts of the data by separating hot and cold data into different streams. Hot data in the first stream maintains frequent updates and merges, while cold data in the second stream undergoes less frequent operations, optimizing each segment for its specific access patterns
2Stability of the object's composition
If LSM trees continuously merge and sort data, then data structure integrity is maintained, but SSD wear increases
Solution Approach 1:
By dividing the data into multiple streams with different retention policies, the patent reduces the frequency and intensity of merging operations that cause SSD wear. The first stream handles recently accessed data with more aggressive merging, while the second stream retains older data with minimal operations, thereby reducing overall write amplification and SSD wear
Solution Approach 2:
The patent implements a mechanism to discard cold data from the first stream and transfer it to the second stream, reducing the amount of data that requires continuous merging and sorting operations. This selective discarding of cold data minimizes unnecessary write operations and extends SSD lifespan
3Measurement precision
If LSM trees maintain sorted key order, then search efficiency is improved, but write amplification increases
Solution Approach 1:
The patent segments the sorted data structure into multiple streams, allowing each stream to maintain its own sorted order independently. This enables selective merging only where necessary, reducing the overall write amplification while preserving search efficiency for both hot and cold data segments
Solution Approach 2:
The patent implements periodic merging operations rather than continuous merging. Data is merged periodically based on access patterns and stream conditions, reducing the frequency of write operations while maintaining sorted order integrity when needed for efficient searches
Data Source
AI summary
Systems and techniques for stream selection from multi-stream storage devices. Notification of a KVS tree write request for a multi-stream storage device is received. The notification includes a KVS tree scope corresponding to data in the write request. A stream identifier (ID) is assigned to the write request based on the KVS tree scope and a stability value of the write request. The stream ID is returned to govern stream assignment to the write request, the stream assignment modifying a write operation of the multi-stream storage device.