One of Rustyll’s most significant advantages over Jekyll is its powerful parallel build system. Built in Rust, Rustyll can utilize all available CPU cores to dramatically speed up site generation.

Enabling Parallel Builds

Parallel builds are enabled by default in Rustyll. You can control the number of threads using the --threads flag:

# Automatically use all available CPU cores
rustyll build --threads auto

# Specify exact number of threads
rustyll build --threads 8

You can also configure this in your _config.yml file:

# Use all available CPU cores
threads: auto

# Or specify a number
threads: 8

Parallel Processing Configuration

For fine-grained control over parallel processing, you can use these additional configuration options:

parallel:
  enabled: true             # Master switch for parallel processing
  markdown: true            # Process markdown in parallel
  layouts: true             # Apply layouts in parallel
  sass: true                # Process Sass/SCSS in parallel
  collections: true         # Process collections in parallel
  
  # Advanced settings
  max_threads_per_task: 4   # Maximum threads per task type
  min_items_per_thread: 5   # Only parallelize when enough items exist

Performance Impact

Parallel processing has a dramatic effect on build times, especially for larger sites:

Site Size	Jekyll	Rustyll	Improvement
Small (50 pages)	5-8s	0.5-1s	8-10x faster
Medium (500 pages)	30-60s	2-5s	12-15x faster
Large (5000+ pages)	5-10min	15-30s	20-30x faster

Understanding Build Stages

Rustyll’s build process is divided into stages, with some stages benefiting more from parallelization than others:

1. File reading and front matter parsing - Highly parallelizable
2. Markdown conversion - Highly parallelizable
3. Template rendering - Moderately parallelizable (some dependencies)
4. Layout application - Moderately parallelizable
5. Writing to disk - I/O bound, less benefit from parallelization

Troubleshooting

If you experience any issues with parallel builds, you can disable them:

rustyll build --threads 1

Or in your configuration:

threads: 1
parallel: false

Combining with Incremental Builds

For the ultimate performance, combine parallel processing with incremental builds:

rustyll build --threads auto --incremental

This will only rebuild files that have changed, and will use all available CPU cores to process them in parallel.

When to Use Parallel Builds

Parallel builds are most beneficial for:

• Large sites with hundreds or thousands of pages
• Sites with complex templates and many includes
• Sites that use extensive Liquid processing
• Development environments that require fast feedback

Best Practices

To get the most out of Rustyll’s parallel build system:

1. Organize related content into collections that can be processed in parallel
2. Use front matter defaults to apply parallel processing settings to groups of files
3. Prioritize important pages with the render_priority front matter setting
4. Enable caching for files that change infrequently
5. Consider your CPU resources - more threads isn’t always better on every system

Comparing with Jekyll

Feature	Jekyll	Rustyll
Build architecture	Sequential	Parallel
Utilizes multiple cores	No	Yes
File reading	Sequential	Parallel
Markdown processing	Sequential	Parallel
Template rendering	Sequential	Parallel
Custom thread configuration	Not available	Available
Per-file parallelization	Not available	Available
Incremental builds	Limited support	Fully supported