HDF5 Go Library

Pure Go implementation of the HDF5 file format - No CGo required

A modern, pure Go library for reading and writing HDF5 files without CGo dependencies. Read support is feature-complete, write support advancing rapidly! v0.11.6-beta: Dataset resizing, variable-length datatypes, and hyperslab selection complete!

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✨ Features

• ✅ Pure Go - No CGo, no C dependencies, cross-platform
• ✅ Modern Design - Built with Go 1.25+ best practices
• ✅ HDF5 Compatibility - Read: v0, v2, v3 superblocks | Write: v0, v2 superblocks
• ✅ Full Dataset Reading - Compact, contiguous, chunked layouts with GZIP
• ✅ Rich Datatypes - Integers, floats, strings (fixed/variable), compounds
• ✅ Memory Efficient - Buffer pooling and smart memory management
• ✅ Production Ready - Read support feature-complete
• ✍️ Comprehensive Write Support - Datasets, groups, attributes + Smart Rebalancing!

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🚀 Quick Start

Installation

go get github.com/scigolib/hdf5

Basic Usage

package main

import (
    "fmt"
    "log"
    "github.com/scigolib/hdf5"
)

func main() {
    // Open HDF5 file
    file, err := hdf5.Open("data.h5")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close()

    // Walk through file structure
    file.Walk(func(path string, obj hdf5.Object) {
        switch v := obj.(type) {
        case *hdf5.Group:
            fmt.Printf("📁 %s (%d children)\n", path, len(v.Children()))
        case *hdf5.Dataset:
            fmt.Printf("📊 %s\n", path)
        }
    })
}

Output:

📁 / (2 children)
📊 /temperature
📁 /experiments/ (3 children)

More examples →

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📚 Documentation

Getting Started

• Installation Guide - Install and verify the library
• Quick Start Guide - Get started in 5 minutes
• Reading Data - Comprehensive guide to reading datasets and attributes

Reference

• Datatypes Guide - HDF5 to Go type mapping
• Troubleshooting - Common issues and solutions
• FAQ - Frequently asked questions
• API Reference - GoDoc documentation

Advanced

• Architecture Overview - How it works internally
• Performance Tuning - B-tree rebalancing strategies for optimal performance
• Rebalancing API - Complete API reference for rebalancing options
• Examples - Working code examples (7 examples with detailed documentation)

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⚡ Performance Tuning

NEW in v0.11.6-beta: Dataset resizing, variable-length datatypes (strings, ragged arrays), and efficient hyperslab selection (data slicing)!

When deleting many attributes, B-trees can become sparse (wasted disk space, slower searches). This library offers 4 rebalancing strategies:

1. Default (No Rebalancing)

Fast deletions, but B-tree may become sparse

// No options = no rebalancing (like HDF5 C library)
fw, err := hdf5.CreateForWrite("data.h5", hdf5.CreateTruncate)

Use for: Append-only workloads, small files (<100MB)

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2. Lazy Rebalancing (10-100x faster than immediate)

Batch processing: rebalances when threshold reached

fw, err := hdf5.CreateForWrite("data.h5", hdf5.CreateTruncate,
    hdf5.WithLazyRebalancing(
        hdf5.LazyThreshold(0.05),         // Trigger at 5% underflow
        hdf5.LazyMaxDelay(5*time.Minute), // Force rebalance after 5 min
    ),
)

Use for: Batch deletion workloads, medium/large files (100-500MB)

Performance: ~2% overhead, occasional 100-500ms pauses

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3. Incremental Rebalancing (ZERO pause)

Background processing: rebalances in background goroutine

fw, err := hdf5.CreateForWrite("data.h5", hdf5.CreateTruncate,
    hdf5.WithLazyRebalancing(),  // Prerequisite!
    hdf5.WithIncrementalRebalancing(
        hdf5.IncrementalBudget(100*time.Millisecond),
        hdf5.IncrementalInterval(5*time.Second),
    ),
)
defer fw.Close()  // Stops background goroutine

Use for: Large files (>500MB), continuous operations, TB-scale data

Performance: ~4% overhead, zero user-visible pause

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4. Smart Rebalancing (Auto-Pilot)

Auto-tuning: library detects workload and selects optimal mode

fw, err := hdf5.CreateForWrite("data.h5", hdf5.CreateTruncate,
    hdf5.WithSmartRebalancing(
        hdf5.SmartAutoDetect(true),
        hdf5.SmartAutoSwitch(true),
    ),
)

Use for: Unknown workloads, mixed operations, research environments

Performance: ~6% overhead, adapts automatically

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Performance Comparison

Mode	Deletion Speed	Pause Time	Use Case
Default	100% (baseline)	None	Append-only, small files
Lazy	95% (10-100x faster than immediate!)	100-500ms batches	Batch deletions
Incremental	92%	None (background)	Large files, continuous ops
Smart	88%	Varies	Unknown workloads

Learn more:

• Performance Tuning Guide: Comprehensive guide with benchmarks, recommendations, troubleshooting
• Rebalancing API Reference: Complete API documentation
• Examples: 4 working examples demonstrating each mode

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🎯 Current Status

Version: v0.11.6-beta (RELEASED 2025-11-06 - Dataset Resize + VLen + Hyperslab) ✅

Production Readiness: Read support feature-complete! Write support advancing rapidly! 🎉

✅ Fully Implemented

• File Structure:

  • Superblock parsing (v0, v2, v3)
  • Object headers v1 (legacy HDF5 < 1.8) with continuations
  • Object headers v2 (modern HDF5 >= 1.8) with continuations
  • Groups (traditional symbol tables + modern object headers)
  • B-trees (leaf + non-leaf nodes for large files)
  • Local heaps (string storage)
  • Global Heap (variable-length data)
  • Fractal heap (direct blocks for dense attributes) ✨ NEW

• Dataset Reading:

  • Compact layout (data in object header)
  • Contiguous layout (sequential storage)
  • Chunked layout with B-tree indexing
  • GZIP/Deflate compression
  • Filter pipeline for compressed data ✨ NEW

• Datatypes (Read + Write):

  • Basic types: int8-64, uint8-64, float32/64
  • Strings: Fixed-length (null/space/null-padded), variable-length (via Global Heap)
  • Advanced types: Arrays, Enums, References (object/region), Opaque
  • Compound types: Struct-like with nested members

• Attributes:

  • Compact attributes (in object header) ✨ NEW
  • Dense attributes (fractal heap foundation) ✨ NEW
  • Attribute reading for groups and datasets ✨ NEW
  • Full attribute API (Group.Attributes(), Dataset.Attributes()) ✨ NEW

• Navigation: Full file tree traversal via Walk()

• Code Quality:

  • Test coverage: 89.7% in internal/ (target: >70%) ✅
  • Lint issues: 0 (34+ linters) ✅
  • TODO items: 0 (all resolved) ✅
  • 57 reference HDF5 test files ✅

⚠️ Partial Support

• Dense Attributes: Infrastructure ready, B-tree v2 iteration deferred to v0.12.0-rc.1 (<10% of files affected)

✍️ Write Support (v0.11.6-beta)

NEW: Advanced Write Features! ✅

Dataset Operations:

• ✅ Create datasets (all layouts: contiguous, chunked, compact)
• ✅ Write data (all standard datatypes)
• ✅ Dataset resizing with unlimited dimensions (NEW!)
• ✅ Variable-length datatypes: strings, ragged arrays (NEW!)
• ✅ Compression (GZIP, Shuffle, Fletcher32)
• ✅ Array and enum datatypes
• ✅ References and opaque types
• ✅ Attribute writing (dense & compact storage)
• ✅ Attribute modification/deletion

Read Enhancements:

• ✅ Hyperslab selection (data slicing) - 10-250x faster! (NEW!)
• ✅ Efficient partial dataset reading
• ✅ Stride and block support
• ✅ Chunk-aware reading (reads ONLY needed chunks)

Known Limitations (v0.11.6-beta):

• ⚠️ Soft/external links (hard links work, MVP APIs exist)
• ⚠️ Compound datatype writing (read works perfectly)
• ⚠️ Some advanced filters

❌ Planned Features

Next Steps - See ROADMAP.md for complete timeline and versioning strategy.

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🔧 Development

Requirements

• Go 1.25 or later
• No external dependencies for the library

Building

# Clone repository
git clone https://github.com/scigolib/hdf5.git
cd hdf5

# Run tests
go test ./...

# Build examples
go build ./examples/...

# Build tools
go build ./cmd/...

Testing

# Run all tests
go test ./...

# Run with race detector
go test -race ./...

# Run with coverage
go test -coverprofile=coverage.out ./...
go tool cover -html=coverage.out

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🤝 Contributing

Contributions are welcome! This is an early-stage project and we'd love your help.

Before contributing:

1. Read CONTRIBUTING.md - Git workflow and development guidelines
2. Check open issues
3. Review the Architecture Overview

Ways to contribute:

• 🐛 Report bugs
• 💡 Suggest features
• 📝 Improve documentation
• 🔧 Submit pull requests
• ⭐ Star the project

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🗺️ Comparison with Other Libraries

Feature	This Library	gonum/hdf5	go-hdf5/hdf5
Pure Go	✅ Yes	❌ CGo wrapper	✅ Yes
Reading	✅ Full (v0.10.0)	✅ Full	❌ Limited
Writing	✅ MVP (v0.11.0)	✅ Full	❌ No
HDF5 1.8+	✅ Yes	⚠️ Limited	❌ No
Advanced Datatypes	✅ Yes (v0.11.0)	✅ Yes	❌ No
Maintained	✅ Active	⚠️ Slow	❌ Inactive
Thread-safe	⚠️ User must sync*	⚠️ Conditional	❌ No

* Different File instances are independent. Concurrent access to same File requires user synchronization (standard Go practice). Full thread-safety with mutexes + SWMR mode planned for v0.12.0-rc.1.

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📖 HDF5 Resources

• HDF5 Format Specification
• Official HDF5 Library
• HDF Group

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📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

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🙏 Acknowledgments

• The HDF Group for the HDF5 format specification
• gonum/hdf5 for inspiration
• All contributors to this project

Special Thanks

Professor Ancha Baranova - This project would not have been possible without her invaluable help and support. Her assistance was crucial in bringing this library to life.

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📞 Support

• 📖 Documentation - Architecture and guides
• 🐛 Issue Tracker
• 💬 Discussions - Community Q&A and announcements
• 🌐 HDF Group Forum - Official HDF5 community discussion

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Status: Beta - Read complete, Write support advancing Version: v0.11.6-beta (Dataset Resize + VLen + Hyperslab + 70.4% Coverage) Last Updated: 2025-11-06

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Built with ❤️ by the HDF5 Go community Recognized by HDF Group Forum ⭐