dsfx/docs/requirements/nfr-2-performance-and-responsiveness.md

NFR-2: Performance & Responsiveness

1. Overview

This document defines the performance and responsiveness criteria that the self-hosted encrypted file storage system must meet. The goal is to ensure that all file operations—including encryption/decryption, file partitioning, upload/download, replication, and synchronization—underpin user interactions with minimal latency and overhead. The system must remain responsive under normal operational loads as well as under simulated adverse conditions using deterministic simulation testing.

2. Objectives & Scope

2.1 Objectives

• Low Latency Operations: Ensure that file uploads, downloads, and internal file processing complete within acceptable response times so that users experience no significant delays.

• High Throughput: Optimize system workflows (e.g., encryption, chunking, replication) to handle multiple simultaneous operations efficiently, thereby supporting scalability.

• Consistent Responsiveness Under Stress: Maintain speedy processing even under conditions of high load, intermittent network conditions, and disk latency or failure scenarios simulated via deterministic testing.

• Predictable and Deterministic Performance: Provide measurable performance benchmarks across various components of the system to allow reliable prediction and repeatability of operations.

2.2 Scope

• Applies to all system modules including client-side file processing (encryption/decryption and file partitioning), server/peer communications, replication processes, and manifest updates.
• Covers performance both in normal operating conditions and simulated adverse scenarios (using the deterministic simulation framework for network/disk conditions).
• Includes interface responsiveness in both the command-line and any future web-based implementations.

3. Detailed Requirements

3.1 File Operation Timeliness

• Encryption/Decryption Overhead:

  • File encryption and decryption operations must complete within a predefined time range relative to file size (e.g., X seconds per MB) under typical hardware conditions.
  • The chosen cryptographic operations (e.g., AES-GCM or ChaCha20-Poly1305) must be benchmarked, and implementations should leverage hardware acceleration where available.

• Chunking and Reassembly Speed:

  • Partitioning a file into chunks (or reassembling chunks back to a file) must be optimized to avoid bottlenecks. Target processing times should be established and validated through benchmarking.

3.2 Network and Communication Performance

• Upload/Download Latency:

  • The latency between initiating a file upload or download and obtaining a response must satisfy predetermined performance targets (e.g., response times within a few hundred milliseconds plus the transmission time).
  • Endpoints must regulate protocol overhead, ensuring that secure channels (e.g., TLS) and custom binary protocols do not adversely affect throughput.

• Inter-Node Communication:

  • Peer-to-peer node communications for replication and synchronization must be optimized for low-latency data transfer.
  • Performance metrics such as handshake times, data transfer latency, and retransmission delays (under simulated adverse network conditions) should be regularly measured and meet target benchmarks.

3.3 System Throughput and Load Handling

• High-Concurrency Support:

  • The system must support multiple simultaneous file operations across different nodes. Concurrency handling mechanisms (such as asynchronous I/O and multithreading) should be in place to avoid performance degradation.
  • Performance tests must be conducted to simulate multiple concurrent users updating files, replicating chunks, and synchronizing manifests.

• Scaling Efficiency:

  • As the number of users, files, or nodes increases, overall system throughput should scale linearly (or near-linearly) with no single performance bottleneck.
  • The system shall define performance baselines against which scaled deployments (e.g., hundreds of nodes or thousands of file operations per minute) can be measured.

3.4 Deterministic Testing and Simulation of Adverse Conditions

• Integration with Simulation Framework:

  • The performance requirement must integrate with the deterministic simulation framework to simulate adverse conditions such as network latency, jitter, and disk I/O delays.
  • Performance tests under these simulation conditions must confirm that the system maintains acceptable response times with gracefully degrading performance rather than catastrophic failure.

• Predictable Recovery:

  • The system must implement robust timeout and retry strategies for transient failures, ensuring that performance remains predictable even under intermittent network or disk disruptions.
  • Comprehensive logging and diagnostic outputs should be available to monitor and tune timeout/retry settings as needed.

3.5 User Interface Responsiveness

• CLI and Web UI Feedback:
  • The user interface should provide immediate feedback on file operation progress (e.g., encryption progress bars, replication status, synchronization updates).
  • UI response times—such as command acknowledgement and display of operation status—must be optimized to deliver a responsive user experience, even in environments under load.

4. Measurable Criteria & Test Cases

4.1 Benchmarking and Profiling

• Per-Operation Benchmarking:
  • Establish benchmarks for typical file sizes (e.g., 1 MB, 10 MB, 100 MB) to measure encryption/decryption times, chunking/reassembly times, and upload/download latency.
  • Use profiling tools to measure CPU, memory, and I/O usage during operation and ensure that system resource consumption remains within acceptable limits.

4.2 Load Testing

• Concurrency Testing:
  • Simulate multiple concurrent file operations to validate the system's scalability.
  • Stress tests should trigger peak loads and record response times, ensuring that performance remains within defined thresholds.

4.3 Simulation Testing

• Injected Network/Disk Latency:

  • Apply the deterministic simulation framework to induce network latency, jitter, and disk I/O delays, then measure the system’s responsiveness under these conditions.
  • Document recovery time for operations after simulated adverse conditions subside.

• Timeout and Retry Efficiency:

  • Test scenarios where connections drop, ensuring that retry logic recovers the operation promptly without significant additional delay.

4.4 End-to-End Operation Tests

• Complete File Transfer:
  • Execute a full cycle of file upload (including client-side encryption, partitioning, transfer) and subsequent download (including decryption and reassembly), measuring total time and per-stage performance.
  • Verify that file integrity is maintained and that individual stage durations meet target performance criteria.

5. Dependencies & Integration Points

• Cryptographic Modules:

  • The performance of encryption/decryption functions (as defined in NFR-1) is a critical dependency.
  • Integration with hardware acceleration components (e.g., AES-NI) must be verified and optimized.

• Network and Communication Modules:

  • Performance of secure communication protocols (as defined in ADR-0007 for client-server and inter-node communications) directly impacts overall responsiveness.

• Simulation Framework:

  • Integration with the deterministic simulation framework is essential to reliably test system behavior under enforced adverse conditions.

• Monitoring Tools:

  • Diagnostic tools and system monitors must be integrated to continuously profile system resource usage and ensure that performance thresholds are met.

6. Security and Responsiveness Considerations

• Balancing Security Overhead:

  • While strong cryptographic measures and secure communication protocols add inherent overhead, these must be balanced with performance optimizations to prevent latency degradation.

• Resource Management:

  • Efficient system resource management (CPU, memory, disk I/O) is crucial to maintaining high throughput. Strategies such as caching, asynchronous processing, and load balancing should be employed.

• Scalability Impact:

  • The system design must account for the impact of scaling on performance and implement mechanisms to mitigate potential bottlenecks that could affect responsiveness.

7. Conclusion

NFR-2 defines the performance and responsiveness criteria that are critical to delivering a seamless, user-friendly experience in the self-hosted encrypted file storage system. By setting measurable benchmarks, integrating robust testing under simulated adverse conditions, and ensuring efficient resource management, the system is designed to maintain low latency and high throughput in both typical and stressed operational environments. These requirements support the overall goals of scalability, efficiency, and user satisfaction while upholding stringent security and privacy standards.