Skiplist Range Query Consistency via Lock-Free Validation
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Solution Overview
Problem
Skiplists face challenges in maintaining consistency during range queries in multicore environments due to phantom key insertions and deletions, which violate transaction consistency, especially when nodes' membership in a key-range changes without detection.
Innovation Solution
A skiplist management system that employs an optimistic transaction model with lock-free execution and a commit protocol to validate range query consistency by tracking nodes during the execution phase and revalidating them during the commit phase, using predecessor nodes to detect phantom nodes and maintaining consistency without relying on node version numbers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Skiplist uses lock-free execution for range queries in multicore environment, then processor contention is prevented and scalability is improved, but transaction consistency cannot be guaranteed due to phantom key insertions and deletions
Solution Approach 1:
The patent applies preliminary action by performing a validation phase before the commit phase. During the validation phase, the system checks for phantom key insertions and deletions by comparing the actual key-range membership with the expected membership. This preliminary validation ensures that any consistency issues are detected before the transaction is committed, thereby maintaining transaction consistency while preserving the lock-free scalable execution model.
2Loss of time
If Skiplist performs range queries without node locking, then operation latency is reduced and throughput is improved, but consistency of key-range membership cannot be maintained due to concurrent insertions and deletions
Solution Approach 1:
The patent implements feedback by introducing a validation mechanism that monitors key-range membership changes during concurrent operations. The system continuously checks whether the membership of keys in the range [A, B] remains consistent with expectations. When inconsistencies are detected (phantom insertions or deletions), the system can abort or retry the transaction. This feedback loop ensures key-range consistency is maintained without requiring traditional locking mechanisms, thus preserving low latency while ensuring reliability.
Data Source
AI summary
In one embodiment, a system for managing a skiplist includes processors arranged for parallel execution of threads, a shared memory storing a skiplist arranged as an ordered set of nodes, and at least one transaction execution thread executed by at least one of the plurality of processors. The at least one transaction execution thread is to execute a range-query operation to identify at least one node of the ordered set of nodes between a first lower key value and a second upper key value, the key-range operation executed by an execution phase and a commit phase, wherein during the execution phase the at least one transaction execution thread traverses nodes of the skiplist in a lock-free state, wherein during the commit phase the at least one transaction execution thread executes a commit protocol that guarantees transaction consistency of the skiplist structure and validates consistency of the range-query operation.