Distributed Transaction Timestamps for Cross-Shard Causal Consistency
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Solution Overview
Problem
Distributed databases face challenges in maintaining causal consistency across horizontally partitioned shards, leading to inconsistencies in transaction execution.
Innovation Solution
Assigning causal timestamps to transactions using a globally coherent time service to ensure the causal order of database transactions, with techniques to wait for a period of time before executing dependent transactions to guarantee the effects of earlier transactions are not visible until their timestamps are in the past.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transactions are executed across horizontally partitioned shards in a distributed database, then search performance and system scalability are improved, but causal consistency of transactions deteriorates
Solution Approach 1:
The system assigns causal timestamps to transactions before execution using a globally coherent time service. This preliminary timestamp assignment establishes a causal order that persists across distributed shards, ensuring that transactions are processed in the correct causal sequence without requiring coordination during execution.
Solution Approach 2:
A globally coherent time service acts as an intermediary between distributed transactions and the database system. This service provides synchronized time intervals that serve as causal timestamps, mediating the causal relationships across partitions without requiring direct communication between shards during transaction execution.
2Reliability
If a wait period is implemented before executing dependent transactions, then causal consistency is ensured, but transaction execution time increases
Solution Approach 1:
Causal timestamps are assigned to all transactions in advance using the globally coherent time service, eliminating the need for wait periods during transaction execution. The preliminary timestamp assignment provides a deterministic causal order that can be enforced without delaying transaction processing.
Data Source
AI summary
The present technology proposes techniques for ensuring globally consistent transactions. This technology may allow distributed systems to ensure the causal order of read and write transactions across different partitions of a distributed database. By assigning causally generated timestamps to the transactions based on one or more globally coherent time services, the timestamps can be used to preserve and represent the causal order of the transactions in the distributed system. In this regard, certain transactions may wait for a period of time after choosing a timestamp in order to delay the start of any second transaction that might depend on it. The wait may ensure that the effects of the first transaction are not made visible until its timestamp is guaranteed to be in the past. This may ensure that a consistent snapshot of the distributed database can be determined for any past timestamp.