CRDT In-Memory Replication with Consensus-Free Re-Sharding
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Solution Overview
Problem
Existing in-memory data structures struggle with implementing conflict-free replicated data types (CRDTs) in distributed systems, as coordination for re-sharding replicas requires consensus, which contradicts the goal of achieving strong eventual consistency without delay.
Innovation Solution
Implement CRDTs in in-memory data structures by using vector clocks (VCs) to manage replicas with different sharding topologies, allowing independent re-sharding without consensus, and employing mechanisms like tombstones, eviction policies, and expiration processes to maintain consistency and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If consensus mechanisms are used for re-sharding replicas, then coordination and consistency are improved, but system delay and reduced availability occur
Solution Approach 1:
The patent extracts the consensus requirement from the re-sharding process. By using CRDTs with vector clocks, the system removes the need for consensus mechanisms during re-sharding operations, allowing replicas to independently re-shard without coordination delays while maintaining eventual consistency through the mathematical properties of CRDTs.
Solution Approach 2:
Each replica independently performs re-sharding operations based on its own vector clock state without requiring service from other replicas or a central coordinator. The CRDT structure enables each node to autonomously determine its sharding topology and migrate data without consensus, achieving self-service re-sharding that eliminates coordination overhead.
2Productivity
If CRDTs are implemented in in-memory data structures, then strong eventual consistency is achieved without consensus, but coordination complexity increases
Solution Approach 1:
The patent replaces the mechanical consensus coordination system with a mathematical CRDT system based on vector clocks and conflict-free replicated data type semantics. This substitution eliminates the need for complex coordination protocols, message exchanges, and consensus algorithms, replacing them with deterministic merge operations that automatically resolve conflicts through the algebraic properties of CRDTs.
3Adaptability or versatility
If multiple replicas with different sharding topologies are maintained, then system flexibility and independent re-sharding are improved, but data consistency management becomes more difficult
Solution Approach 1:
The patent uses vector clocks as dynamic parameters that automatically adjust to track the state of each replica across different sharding topologies. Each replica maintains its own sharding configuration independently, and the vector clock parameters enable the system to track causal relationships and ensure consistency despite topology changes, allowing flexible re-sharding without increasing consistency management complexity.
Data Source
AI summary
Mechanisms, including systems, methods, and non-transitory computer readable media, for implementing conflict-free replicated data types in in-memory data structures are provided, the mechanisms comprising: a memory; and at least one hardware processor coupled to the memory and collectively configured to: mark a first key of a conflict-free replicated data type as to be deleted; send an update message reflecting that the first key is to be deleted to a first replica of an in-memory data structure; receive a plurality of messages each acknowledging that the first key is to be deleted; determine that the plurality of messages includes a message for each of a plurality of shards of the first replica; and in response to determining that the plurality of messages includes a message for each of the plurality of shards of the first replica, delete the first key.