Configuration Change Control in Distributed Total Order Broadcast Systems
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Solution Overview
Problem
In distributed systems performing total order broadcast, changing the system configuration while maintaining continuous processing is challenging due to state inconsistencies between client and server devices, leading to delays and retransmission procedures.
Innovation Solution
A computer system with input units that send clock time notifications and data notifications to storage units, and a configuration change control device that manages the addition of new input units by delaying consensus confirmation with a predetermined window interval, ensuring data broadcast order and minimizing waiting times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the system configuration is changed by adding a new input unit while maintaining continuous processing, then high availability and minimal processing delay are improved, but state inconsistency between client and server devices occurs leading to processing delays and retransmission procedures
Solution Approach 1:
The system performs preliminary actions by having the new input unit send empty notifications for all clock times before it started operation. This preliminary notification ensures that server devices have complete state information from all input units before consensus confirmation begins, preventing state inconsistency and retransmission delays while maintaining continuous processing
Solution Approach 2:
Empty notifications act as an intermediary mechanism between the new input unit and server devices. These notifications bridge the state inconsistency by providing placeholder information for time periods when the new input unit was not operational, allowing consensus confirmation to proceed accurately without waiting for actual data that cannot be generated
2Measurement precision
If the storage unit waits for state information from all input units before confirming consensus, then ordering accuracy is improved, but processing delay increases during configuration changes
Solution Approach 1:
The new input unit sends empty notifications preliminarily for all clock times before its operational start. This allows server devices to have complete state information available immediately, enabling consensus confirmation to proceed without waiting for the new input unit to generate actual data, thus maintaining ordering accuracy while minimizing confirmation time
Solution Approach 2:
The system skips the waiting period by using empty notifications to represent time periods when the new input unit was not operational. Instead of waiting for the new input unit to catch up or generate data for past time periods, the system rushes through the consensus confirmation process with the preliminary empty notifications already in place, maintaining accuracy while reducing delay
Data Source
AI summary
Upon receiving an input of data, an input unit transmits a time notification to another input unit and transmits a data notification including the input clock time to a storage unit. Upon receiving a time notification from another input unit, the input unit transmits an empty notification including the input clock time to the storage unit to indicate there is no input before the input clock time. Upon receiving the data notification from an input unit having received the input of data and receiving the notification from the other input unit, the storage unit broadcasts the data in order, assuming that consensus of the plurality of storage units is confirmed. When adding an input unit to a computer system, a control device causes the storage unit to start confirming the consensus including the joining input unit after a window interval has elapsed after the joining input unit starts operation.