FPGA Hash Table Block Sub-Block Segmentation
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Solution Overview
Problem
Existing hash table implementations on Field-Programmable Gate Arrays (FPGAs) face challenges in achieving high space efficiency and throughput due to hash collisions, requiring frequent rebuilds, which degrade performance and increase logic complexity, especially when input key characteristics are unknown or change during operation.
Innovation Solution
A method is introduced to build a hash table by dividing it into blocks and sub-blocks, using different association patterns between keys and locations within each block, allowing for efficient key storage and retrieval without the need for complex operations like multiplication, ensuring space efficiency and high throughput even with small-capacity memory blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a hash table is rebuilt when space efficiency and throughput decrease due to hash collisions, then space efficiency is improved, but throughput is degraded and logic complexity increases
Solution Approach 1:
The hash table is divided into multiple blocks, each with its own hash function. When collisions occur in one block, only that block needs to be rebuilt rather than the entire hash table, reducing the impact on throughput and logic complexity while maintaining space efficiency.
Solution Approach 2:
The system dynamically selects different hash functions for different blocks based on input key characteristics. This allows the hash table to adapt to varying data patterns without requiring a complete rebuild, maintaining both space efficiency and throughput.
2Manufacturing precision
If the hash table is rebuilt to improve space efficiency, then space efficiency is improved, but device complexity increases due to additional rebuild mechanism logics
Solution Approach 1:
By segmenting the hash table into blocks with independent hash functions, the rebuild logic is distributed across blocks rather than requiring a single complex global rebuild mechanism, reducing overall device complexity.
Solution Approach 2:
Each block has its own hash function and rebuild logic tailored to local conditions. This localizes the complexity to small, manageable units rather than requiring complex global coordination logic.
3Manufacturing precision
If multiplication and remainder calculation are used for hash function as in universal hashing, then hash function quality is improved, but calculation time increases beyond one clock cycle
Solution Approach 1:
The patent replaces multiplication and remainder calculation with XOR-based hash functions that can be computed in a single clock cycle using simple logic gates, eliminating the need for complex arithmetic operations while maintaining hash function quality.
Solution Approach 2:
The hash function parameters are changed from arithmetic operations (multiplication, remainder) to bitwise operations (XOR, shift), fundamentally changing the computational approach to achieve both quality and speed requirements.
4Manufacturing precision
If FPGA is reprogrammed to optimize hash function according to input key characteristics, then hash function quality is improved, but operation flexibility is reduced due to reprogramming requirement
Solution Approach 1:
The system uses multiple configurable hash functions that can be dynamically selected and switched during operation based on input key characteristics, eliminating the need for reprogramming while maintaining optimal hash function quality.
Solution Approach 2:
The FPGA is designed with multiple hash function units that can handle different input key characteristics, making the device universally adaptable to various data patterns without requiring external reprogramming.
Data Source
AI summary
A method, a computer system, and/or a computer program product are disclosed. One computer-implemented method for building a hash table includes dividing a hash table into plural blocks; and dividing each block into plural sub-blocks. A certain sub-block uses a first pattern of association between a key and a location for storing the key. Another sub-block which belongs to the same block having the certain sub-block uses a second pattern which is different from the first pattern. The method may further include building a hash table by using memory blocks in a Field Programmable Gate Array.