Cache Freshness Validation Using a Guaranteed Clock
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Solution Overview
Problem
Traditional data center caches cannot guarantee that the data retrieved is current, as they may contain stale information, despite efforts to mitigate this through techniques like cache invalidation and time-to-live policies.
Innovation Solution
A cache system that utilizes a guaranteed clock value from an authoritative database and a data invalidation technique to ensure that only data valid up to a specific point in time is returned, ensuring data accuracy by repeatedly polling the database for changes to the root object.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional cache invalidation and time-to-live policies are used, then data freshness is improved, but data accuracy cannot be guaranteed
Solution Approach 1:
The system implements a feedback mechanism where the cache continuously receives guaranteed clock values from the authoritative database and uses this feedback to validate data freshness. When a request comes in, the system checks whether the requested data is still valid according to the latest guaranteed clock value, and only returns data that is guaranteed to be current, thus ensuring both freshness and accuracy.
Solution Approach 2:
The authoritative database performs preliminary action by continuously updating and publishing guaranteed clock values before data requests are made. This preliminary establishment of a trusted time reference allows the cache to proactively validate data freshness without needing to perform expensive real-time consistency checks during request processing.
2Measurement precision
If the cache repeatedly polls the database for changes, then data accuracy is improved, but system complexity increases
Solution Approach 1:
The system introduces a guaranteed clock value as an intermediary mechanism between the authoritative database and the cache. Instead of the cache directly polling the database for changes (which would increase complexity), the database publishes guaranteed clock values that serve as a mediator. The cache simply compares requested data against this intermediary time reference to determine freshness, significantly simplifying the validation process.
3Reliability
If hybrid logical clock is used to synchronize with physical time, then data currentness is improved, but implementation complexity increases
Solution Approach 1:
The system changes the parameter used for time tracking from physical timestamps to guaranteed clock values that are derived from hybrid logical clocks. This parameter change allows the system to maintain data currentness by comparing logical time ordering rather than physical timestamps, which can be problematic in distributed systems. The guaranteed clock values provide a simplified, reliable time parameter that easier to implement while ensuring data freshness.
Data Source
AI summary
The present technology is a cache that provides an implied guarantee that data returned in response to a query is current. The cache uses two techniques together to guarantee that data returned in response to a query from the cache is current. The first technique is a guaranteed clock value. The is a clock value for which all changes that have occurred before it have been written to the authoritative database. Any query having a clock value greater than the guaranteed clock value is invalid. The second technique is a data invalidation technique, where the cache repeatedly polls the authoritative database for information about changes and invalidates objects associated with changes. If no change has happened, the cache can confidently conclude it is up to date since the cache knows that it is aware of all changes as of the guaranteed clock value.