LSM Tree Defragmentation During Re-Compaction to Cut Amplification
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Solution Overview
Problem
Traditional relational databases face limitations in scalability, memory usage, and performance due to their predefined structure, while key-value stores suffer from fragmentation and high read and write amplification during re-compaction of keys in log structured merge trees, leading to inefficiencies in storage and retrieval operations.
Innovation Solution
Implementing a defragmentation process during re-compaction of keys within a log structured merge tree to store keys with the same prefixes together, using in-memory hashes to reduce search overhead, and prefetching keys for garbage collection to improve efficiency and reduce read and write amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If re-compaction of keys is performed in log structured merge tree, then storage organization is improved, but read and write amplification increases
Solution Approach 1:
The patent applies preliminary action by prefetching keys from the log structured merge tree before they are needed for garbage collection. This advance preparation reduces the need for immediate read operations during compaction, thereby lowering read amplification while maintaining effective storage reorganization.
Solution Approach 2:
The patent implements continuity of useful action by performing defragmentation continuously during the re-compaction process rather than as a separate operation. This integrated approach ensures that keys are reorganized and defragmented in a continuous flow, reducing the total number of write operations and minimizing write amplification.
2Ease of manufacture
If keys are stored fragmented in log structured merge tree, then write operations are simplified, but read operations become inefficient
Solution Approach 1:
The patent extracts the defragmentation function as a separate preprocessing step that identifies and relocates fragmented keys before read operations occur. By taking out the fragmented keys and reorganizing them contiguously, the system maintains simple write operations while dramatically improving read operation efficiency through contiguous key storage.
3Quantity of substance
If defragmentation is performed during re-compaction, then storage efficiency is improved, but process complexity increases
Solution Approach 1:
The patent merges the defragmentation process with the existing re-compaction operation, combining two functions into a single integrated process. This merging approach improves storage efficiency by defragmenting keys during compaction while avoiding the overhead of a separate defragmentation process, thus not increasing overall system complexity.
Solution Approach 2:
The system performs self-service by automatically managing the defragmentation during re-compaction without requiring external intervention or complex scheduling. The log structured merge tree itself facilitates the defragmentation through its inherent re-compaction mechanism, making the process self-sufficient and reducing overall system complexity.
Data Source
AI summary
Techniques are provided for implementing a defragmentation process during a merge operation performed by a re-compaction process upon a log structured merge tree. The log structured merge tree is used to store keys of key-value pairs within a key-value store. As the log structured merge tree fills with keys over time, the re-compaction process is performed to merge keys down to lower levels of the log structured merge tree to re-compact the keys. Re-compaction can result in fragmentation because there is a lack of spatial locality of where the re-compaction operations re-writes the keys within storage. Fragmentation increases read and write amplification when accessing the keys stored in different locations within the storage. Accordingly, the defragmentation process is performed during a last merge operation of the re-compaction process in order to store keys together within the storage, thus reducing read and write amplification when accessing the keys.