Overview
========

DFAnalyzer is an open-source tool for analyzing performance data from large-scale workflows on distributed systems. It presents a hierarchical, layer-by-layer summary of an application's execution, from high-level application events down to low-level POSIX calls. For each layer, DFAnalyzer quantifies time, operation counts, and data volume, and calculates key performance metrics like bandwidth and operations per second. It also visualizes the overlap between different layers, helping to characterize and understand complex I/O and compute patterns.

What DFAnalyzer Solves
----------------------

As an HPC user or system administrator, you may encounter these common I/O challenges:

- **Unexplained performance degradation** during application runs with unclear causes
- **Complex I/O patterns** across distributed resources that are difficult to analyze manually
- **Large volumes of performance data** that are overwhelming to sift through
- **Hidden performance issues** that standard profiling tools might miss
- **Resource underutilization** due to unoptimized I/O strategies

How DFAnalyzer Works
--------------------

DFAnalyzer makes analyzing complex I/O issues simple with a straightforward workflow:

.. mermaid::

   flowchart LR
    A[Run Your Application] --> B[Collect I/O Traces]
    B --> C[Run DFAnalyzer Analysis]
    C --> D[Review Insights]
    D --> E[Apply Fixes]
    E --> F[Verify Improvements]

Simple 4-Step Process
~~~~~~~~~~~~~~~~~~~~~

1. **Collect**: Run your HPC application with DFTracer or another I/O tracer
2. **Analyze**: Feed your trace data into DFAnalyzer
3. **Review**: Examine the detailed performance reports
4. **Optimize**: Apply changes to your application or system based on the analysis

The entire process is designed to be lightweight and non-intrusive to your workflow, with minimal setup required.

Key Features
------------

Multi-Perspective Analysis
~~~~~~~~~~~~~~~~~~~~~~~~~~

DFAnalyzer doesn't just look at your I/O problems from one angle - it examines them from multiple perspectives to ensure nothing is missed. This approach finds issues that would be missed by tools that only look at a single aspect of I/O performance. For example, a performance issue might only appear when specific processes access particular files during certain time periods - DFAnalyzer can detect these complex patterns.

Smart Diagnostics Engine
~~~~~~~~~~~~~~~~~~~~~~~~

DFAnalyzer's intelligent analysis engine provides detailed performance information. The engine:

- Highlights areas of high impact on performance
- Provides detailed analysis of performance characteristics
- Presents data in clear, human-readable language
- Allows you to add custom rules for your specific environment

Designed for Scale
~~~~~~~~~~~~~~~~~~

DFAnalyzer handles your data efficiently, no matter how large your workflow:

- **Fast Analysis**: Process multi-terabyte datasets in minutes rather than hours
- **Out-of-Core Processing**: Works well even on systems with limited memory
- **Parallel Processing**: Utilizes available computing resources to speed up analysis

Who Should Use DFAnalyzer
-------------------------

DFAnalyzer is ideal for:

- **HPC Application Developers** looking to optimize I/O performance
- **System Administrators** trying to diagnose storage performance issues
- **Researchers** working with data-intensive scientific workflows

Common Scenarios
----------------

Here are some common scenarios where DFAnalyzer helps users:

1. **Application Performance Analysis**: "My simulation runs slower than expected and I don't know why."

   - *DFAnalyzer identifies unbalanced I/O patterns and provides detailed diagnostics*

2. **Storage System Analysis**: "Our file system performance isn't matching the hardware specifications."

   - *DFAnalyzer reveals specific I/O patterns that impact system performance*

3. **Workflow Investigation**: "Some stages of our pipeline are much slower than others."
   
   - *DFAnalyzer helps pinpoint where and when performance issues occur in multi-stage workflows*

Getting Started
---------------

Ready to analyze your I/O performance? See our :doc:`getting-started` for:

- Installation instructions
- Basic usage examples
- Command-line interface tutorial
- Sample analysis reports
