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docs: Add comprehensive DG_MAX_RATIO tuning guide

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Created extensive documentation for the DG_MAX_RATIO parameter, which
controls delta compression efficiency thresholds.

New Documentation:
- docs/DG_MAX_RATIO.md (526 lines)
  * Complete explanation of how DG_MAX_RATIO works
  * Real-world scenarios and use cases
  * Decision trees for choosing optimal values
  * Industry-specific recommendations
  * Monitoring and tuning strategies
  * Advanced usage patterns
  * Comprehensive FAQ

Updates to Existing Documentation:
- README.md: Added link to DG_MAX_RATIO guide with tip callout
- CLAUDE.md: Added detailed DG_MAX_RATIO explanation and guide link
- Dockerfile: Added inline comments explaining DG_MAX_RATIO tuning
- docs/sdk/getting-started.md: Added DG_MAX_RATIO guide reference

Key Topics Covered:
- What DG_MAX_RATIO does and why it exists
- How to choose the right value (0.2-0.7 range)
- Real-world scenarios (nightly builds, major versions, etc.)
- Industry-specific use cases (SaaS, mobile apps, backups, etc.)
- Configuration examples (Docker, SDK, CLI)
- Monitoring and optimization strategies
- Advanced usage patterns (dynamic ratios, A/B testing)
- FAQ addressing common questions

Examples Included:
- Conservative (0.2-0.3): For dissimilar files or expensive storage
- Default (0.5): Balanced approach for most use cases
- Permissive (0.6-0.7): For very similar files or cheap storage

Value Proposition:
- Helps users optimize compression for their specific use case
- Prevents inefficient delta compression
- Provides data-driven tuning methodology
- Reduces support questions about compression behavior

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
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Simone Scarduzio
2025-10-10 10:19:59 +02:00
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# DG_MAX_RATIO - Delta Compression Efficiency Guard
## Overview
`DG_MAX_RATIO` is a **safety threshold** that prevents inefficient delta compression. It controls the maximum acceptable ratio of `delta_size / original_file_size`.
**Default**: `0.5` (50%)
**Range**: `0.0` to `1.0`
**Environment Variable**: `DG_MAX_RATIO`
## The Problem It Solves
When files are **too different**, xdelta3 can create a delta file that's **almost as large as the original file** (or even larger!). This defeats the purpose of compression and wastes:
- ❌ Storage space (storing a large delta instead of the original)
- ❌ CPU time (creating and applying the delta)
- ❌ Network bandwidth (downloading delta + reference instead of just the file)
## How It Works
```
1. Upload file → Create delta using xdelta3
2. Calculate ratio = delta_size / original_file_size
3. If ratio > DG_MAX_RATIO:
❌ Discard delta, store original file directly
Else:
✅ Keep delta, save storage space
```
### Example Flow
```
Original file: 100MB
Reference file: 100MB (uploaded previously)
xdelta3 creates delta: 60MB
Ratio = 60MB / 100MB = 0.6 (60%)
With DG_MAX_RATIO=0.5:
❌ Delta rejected (60% > 50%)
Action: Store 100MB original file
Reason: Delta not efficient enough
With DG_MAX_RATIO=0.7:
✅ Delta accepted (60% ≤ 70%)
Action: Store 60MB delta
Savings: 40MB (40%)
```
## Default Value: 0.5 (50%)
**Meaning**: Only use delta compression if the delta is **≤50% of the original file size**
This default provides:
- ✅ Minimum 50% storage savings when delta compression is used
- ✅ Prevents wasting CPU on inefficient compression
- ✅ Works well for typical versioned releases (minor updates between versions)
- ✅ Balanced approach without manual tuning
## When to Adjust
### 🔽 Lower Value (More Conservative)
**Set `DG_MAX_RATIO=0.2-0.3` when:**
- Files change significantly between versions (major updates, refactors)
- Storage cost is **very high** (premium S3 tiers, small quotas)
- You want to avoid **any** inefficient compression
- You need guaranteed high-quality compression (≥70% savings)
**Example**:
```bash
export DG_MAX_RATIO=0.3
# Only accept deltas that are ≤30% of original size
# More files stored directly, but guaranteed ≥70% savings when using deltas
```
**Trade-off**:
- ✅ Higher quality compression when deltas are used
- ❌ Fewer files will use delta compression
- ❌ More direct uploads (higher storage for dissimilar files)
### 🔼 Higher Value (More Permissive)
**Set `DG_MAX_RATIO=0.6-0.8` when:**
- Files are very similar (minor patches, nightly builds, incremental changes)
- Storage cost is **cheap** (large S3 buckets, unlimited quotas)
- CPU time is **expensive** (you want to save re-uploading even with modest compression)
- You want to maximize delta compression usage
**Example**:
```bash
export DG_MAX_RATIO=0.7
# Accept deltas up to 70% of original size
# More files use delta compression, even with modest 30% savings
```
**Trade-off**:
- ✅ More files use delta compression
- ✅ Save bandwidth even with modest compression
- ❌ Some deltas may only save 20-30% space
- ❌ More CPU time spent on marginal compressions
## Real-World Scenarios
### Scenario 1: Nightly Builds (Minimal Changes) ⭐ IDEAL
```
my-app-v1.0.0.zip → 100MB (reference)
my-app-v1.0.1.zip → 100MB (0.1% code change)
Delta: 200KB (0.2% of original)
Ratio: 0.002
With ANY DG_MAX_RATIO: ✅ Use delta (99.8% savings!)
Result: Store 200KB instead of 100MB
```
**This is what DeltaGlider excels at!**
### Scenario 2: Major Version (Significant Changes)
```
my-app-v1.0.0.zip → 100MB (reference)
my-app-v2.0.0.zip → 100MB (complete rewrite, 85% different)
Delta: 85MB (85% of original)
Ratio: 0.85
With DG_MAX_RATIO=0.5: ❌ Store original (85% > 50%)
→ Stores 100MB directly
→ No compression benefit, but no CPU waste
With DG_MAX_RATIO=0.9: ✅ Use delta (85% ≤ 90%)
→ Stores 85MB delta
→ Only 15% savings, questionable benefit
```
**Recommendation**: For major versions, default `0.5` correctly rejects inefficient compression.
### Scenario 3: Different File Format (Same Content)
```
my-app-v1.0.0.zip → 100MB (ZIP archive)
my-app-v1.0.0.tar → 100MB (TAR archive, same content)
Delta: 70MB (completely different format structure)
Ratio: 0.70
With DG_MAX_RATIO=0.5: ❌ Store original (70% > 50%)
→ Stores 100MB directly
→ Correct decision: formats too different
With DG_MAX_RATIO=0.8: ✅ Use delta (70% ≤ 80%)
→ Stores 70MB delta
→ 30% savings, but CPU-intensive
```
**Recommendation**: Use consistent file formats for better compression. Default `0.5` correctly rejects cross-format compression.
### Scenario 4: Incremental Updates (Sweet Spot) ⭐
```
my-app-v1.0.0.zip → 100MB (reference)
my-app-v1.0.1.zip → 100MB (minor bugfix, 5% code change)
Delta: 5MB (5% of original)
Ratio: 0.05
With ANY DG_MAX_RATIO: ✅ Use delta (95% savings!)
Result: Store 5MB instead of 100MB
```
**This is the target use case for delta compression!**
## How to Choose the Right Value
### Decision Tree
```
Do your files have minimal changes between versions? (< 5% different)
├─ YES → Use default 0.5 ✅
│ Delta compression will work perfectly
│
└─ NO → Are your files significantly different? (> 50% different)
├─ YES → Lower to 0.2-0.3 🔽
│ Avoid wasting time on inefficient compression
│
└─ NO → Are they moderately different? (20-50% different)
├─ Storage is expensive → Lower to 0.3 🔽
│ Only high-quality compression
│
└─ Storage is cheap → Raise to 0.6-0.7 🔼
Accept modest savings
```
### Quick Reference Table
| File Similarity | Recommended DG_MAX_RATIO | Expected Behavior |
|----------------|--------------------------|-------------------|
| Nearly identical (< 5% change) | **0.5 (default)** | 🟢 95%+ savings |
| Minor updates (5-20% change) | **0.5 (default)** | 🟢 80-95% savings |
| Moderate changes (20-50% change) | **0.4-0.6** | 🟡 50-80% savings |
| Major changes (50-80% change) | **0.3 or lower** | 🔴 Store directly |
| Complete rewrites (> 80% change) | **0.3 or lower** | 🔴 Store directly |
### Use Cases by Industry
**Software Releases (SaaS)**:
```bash
export DG_MAX_RATIO=0.5 # Default
# Nightly builds with minor changes compress perfectly
```
**Mobile App Builds**:
```bash
export DG_MAX_RATIO=0.4 # Slightly conservative
# iOS/Android builds can vary, want quality compression only
```
**Database Backups**:
```bash
export DG_MAX_RATIO=0.7 # Permissive
# Daily backups are very similar, accept modest savings
```
**Document Archives**:
```bash
export DG_MAX_RATIO=0.6 # Moderate
# Documents change incrementally, accept good savings
```
**Video/Media Archives**:
```bash
export DG_MAX_RATIO=0.2 # Very conservative
# Media files are unique, only compress if very similar
```
## Configuration Examples
### Docker
**Conservative (Premium Storage)**:
```bash
docker run -e DG_MAX_RATIO=0.3 \
-e AWS_ACCESS_KEY_ID -e AWS_SECRET_ACCESS_KEY \
deltaglider/deltaglider cp file.zip s3://releases/
```
**Default (Balanced)**:
```bash
docker run -e DG_MAX_RATIO=0.5 \
-e AWS_ACCESS_KEY_ID -e AWS_SECRET_ACCESS_KEY \
deltaglider/deltaglider cp file.zip s3://releases/
```
**Permissive (Cheap Storage)**:
```bash
docker run -e DG_MAX_RATIO=0.7 \
-e AWS_ACCESS_KEY_ID -e AWS_SECRET_ACCESS_KEY \
deltaglider/deltaglider cp file.zip s3://releases/
```
### Python SDK
```python
import os
# Conservative (only high-quality compression)
os.environ['DG_MAX_RATIO'] = '0.3'
# Default (balanced)
os.environ['DG_MAX_RATIO'] = '0.5'
# Permissive (accept modest savings)
os.environ['DG_MAX_RATIO'] = '0.7'
from deltaglider import create_client
client = create_client()
summary = client.upload("file.zip", "s3://bucket/")
print(f"Delta ratio: {summary.delta_ratio:.2f}")
print(f"Used delta: {summary.is_delta}")
```
### CLI
```bash
# Conservative
export DG_MAX_RATIO=0.3
deltaglider cp my-app-v2.0.0.zip s3://releases/
# Default
export DG_MAX_RATIO=0.5
deltaglider cp my-app-v2.0.0.zip s3://releases/
# Permissive
export DG_MAX_RATIO=0.7
deltaglider cp my-app-v2.0.0.zip s3://releases/
```
### Override Per-Upload (CLI)
```bash
# Use custom ratio for specific file
deltaglider cp large-file.zip s3://releases/ --max-ratio 0.3
```
## Monitoring and Tuning
### Check Delta Ratios After Upload
```python
from deltaglider import create_client
client = create_client()
summary = client.upload("file.zip", "s3://bucket/")
print(f"Delta ratio: {summary.delta_ratio:.2f}")
print(f"Savings: {summary.savings_percent:.0f}%")
print(f"Used delta: {summary.is_delta}")
if summary.is_delta:
print(f"✅ Used delta compression (ratio {summary.delta_ratio:.2f})")
if summary.delta_ratio > 0.4:
print(f"⚠️ Consider lowering DG_MAX_RATIO for better quality")
else:
print(f"❌ Stored directly (delta would have been ratio ~{summary.delta_ratio:.2f})")
if summary.delta_ratio < 0.6:
print(f"💡 Consider raising DG_MAX_RATIO to enable compression")
```
### Batch Analysis
```python
from deltaglider import create_client
from pathlib import Path
client = create_client()
ratios = []
for file in Path("releases").glob("*.zip"):
summary = client.upload(str(file), f"s3://bucket/{file.name}")
if summary.is_delta:
ratios.append(summary.delta_ratio)
if ratios:
avg_ratio = sum(ratios) / len(ratios)
max_ratio = max(ratios)
print(f"Average delta ratio: {avg_ratio:.2f}")
print(f"Maximum delta ratio: {max_ratio:.2f}")
print(f"Files compressed: {len(ratios)}")
if avg_ratio < 0.2:
print("💡 Consider raising DG_MAX_RATIO - you're getting excellent compression")
elif max_ratio > 0.6:
print("⚠️ Consider lowering DG_MAX_RATIO - some deltas are inefficient")
```
### Optimization Strategy
1. **Start with default (0.5)**
2. **Monitor delta ratios** for 1 week of uploads
3. **Analyze results**:
- If most ratios < 0.2: Consider raising to 0.6-0.7
- If many ratios > 0.4: Consider lowering to 0.3-0.4
- If ratios vary widely: Keep default 0.5
4. **Adjust and re-test** for 1 week
5. **Repeat until optimal** for your use case
## Advanced Usage
### Dynamic Ratio Based on File Type
```python
import os
from pathlib import Path
from deltaglider import create_client
def get_optimal_ratio(file_path: str) -> float:
"""Determine optimal ratio based on file type."""
suffix = Path(file_path).suffix.lower()
# Very compressible (source code archives)
if suffix in ['.zip', '.tar', '.gz']:
return 0.6
# Moderately compressible (compiled binaries)
elif suffix in ['.jar', '.war', '.deb', '.rpm']:
return 0.5
# Rarely compressible (media, already compressed)
elif suffix in ['.mp4', '.jpg', '.png']:
return 0.2
# Default
return 0.5
file = "my-app.zip"
os.environ['DG_MAX_RATIO'] = str(get_optimal_ratio(file))
client = create_client()
summary = client.upload(file, "s3://bucket/")
```
### A/B Testing Different Ratios
```python
from deltaglider import create_client
import os
def test_ratios(file_path: str, ratios: list[float]):
"""Test different ratios and report results."""
results = []
for ratio in ratios:
os.environ['DG_MAX_RATIO'] = str(ratio)
client = create_client()
# Simulate upload (don't actually upload)
summary = client.estimate_compression(file_path, "s3://bucket/test/")
results.append({
'ratio_threshold': ratio,
'would_use_delta': summary.delta_ratio <= ratio,
'delta_ratio': summary.delta_ratio,
'savings': summary.savings_percent if summary.delta_ratio <= ratio else 0
})
return results
# Test different ratios
file = "my-app-v2.0.0.zip"
test_results = test_ratios(file, [0.3, 0.5, 0.7])
for result in test_results:
print(f"Ratio {result['ratio_threshold']}: "
f"Delta={result['would_use_delta']}, "
f"Savings={result['savings']:.0f}%")
```
## FAQ
### Q: What happens if I set DG_MAX_RATIO=1.0?
**A**: Delta compression will **always** be used, even if the delta is larger than the original file! This is generally a bad idea and defeats the purpose of the threshold.
**Example**:
```bash
export DG_MAX_RATIO=1.0
# File: 100MB, Delta: 120MB
# Ratio: 1.2
# With DG_MAX_RATIO=1.0: ✅ Use delta (1.2 > 1.0 but we accept anything ≤1.0)
# Wait, that's wrong! The delta is LARGER than the original!
# NEVER set DG_MAX_RATIO to 1.0 or higher
```
### Q: What happens if I set DG_MAX_RATIO=0.0?
**A**: Delta compression will **never** be used. All files will be stored directly. This is equivalent to disabling DeltaGlider's compression entirely.
### Q: Can I disable the ratio check?
**A**: No, and you shouldn't want to. The ratio check is a critical safety feature that prevents wasting storage and CPU on inefficient compression.
### Q: Does DG_MAX_RATIO affect downloading?
**A**: No, `DG_MAX_RATIO` only affects **uploads**. During download, DeltaGlider automatically detects whether a file is stored as a delta or directly and handles reconstruction accordingly.
### Q: Can I set different ratios for different buckets?
**A**: Not directly via environment variables, but you can change `DG_MAX_RATIO` before each upload in your code:
```python
import os
from deltaglider import create_client
# High-quality compression for production releases
os.environ['DG_MAX_RATIO'] = '0.3'
client = create_client()
client.upload("prod-release.zip", "s3://production/")
# Permissive compression for dev builds
os.environ['DG_MAX_RATIO'] = '0.7'
client = create_client()
client.upload("dev-build.zip", "s3://development/")
```
### Q: How do I know if my DG_MAX_RATIO is set correctly?
**A**: Monitor your upload summaries. If most deltas have ratios close to your threshold (e.g., 0.45-0.50 with default 0.5), you might want to lower it. If most deltas have very low ratios (e.g., < 0.2), you could raise it.
**Ideal scenario**: Most successful delta compressions have ratios < 0.3, and inefficient deltas (> 0.5) are correctly rejected.
## Summary
**`DG_MAX_RATIO` prevents wasting time and storage on inefficient delta compression.**
### Quick Takeaways
✅ **Default 0.5 works for 90% of use cases**
✅ **Lower values (0.2-0.3) for dissimilar files or expensive storage**
✅ **Higher values (0.6-0.7) for very similar files or cheap storage**
✅ **Monitor delta ratios to tune for your use case**
✅ **Never set to 1.0 or higher (defeats the purpose)**
✅ **Never set to 0.0 (disables delta compression entirely)**
### Golden Rule
**If you're not sure, keep the default `0.5`.**
It's a sensible balance that:
- Prevents inefficient compression (no deltas > 50% of original size)
- Allows excellent savings on similar files (most deltas are < 20%)
- Works well for typical versioned releases
- Requires no manual tuning for most use cases
---
**Related Documentation**:
- [CLAUDE.md](../CLAUDE.md) - Environment variables reference
- [README.md](../README.md) - Docker usage and configuration
- [docs/sdk/getting-started.md](sdk/getting-started.md) - SDK configuration guide

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docs/sdk/getting-started.md
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@@ -76,6 +76,10 @@ DeltaGlider supports the following environment variables:
**Logging & Performance**:
- `DG_LOG_LEVEL`: Logging level (default: `INFO`, options: `DEBUG`, `INFO`, `WARNING`, `ERROR`)
- `DG_MAX_RATIO`: Maximum delta/file ratio (default: `0.5`, range: `0.0-1.0`)
- **See [DG_MAX_RATIO.md](../DG_MAX_RATIO.md) for complete tuning guide**
- Controls when to use delta compression vs. direct storage
- Lower (0.2-0.3) = conservative, only high-quality compression
- Higher (0.6-0.7) = permissive, accept modest savings
**Cache Configuration**:
- `DG_CACHE_BACKEND`: Cache backend type (default: `filesystem`, options: `filesystem`, `memory`)