Freeze a Page to Cache Outputs

A live demonstration of page-level freeze. The code cells below were executed once and cached — subsequent builds reuse the output without re-running.

This page is a live proof that page-level freeze works. The code cells below were executed once via great-docs freeze, and their outputs are persisted in the repository’s _freeze/ directory. Every subsequent great-docs build reuses these cached outputs without re-executing the code.

How to verify this works

Look at the “Executed at” timestamp below. If it shows a date in the past (not today’s date), that means the code was not re-executed during this build — the output was loaded from the freeze cache.

Cached Computation

import datetime
import hashlib
import platform
import time

# Record when this cell actually executed
executed_at = datetime.datetime.now()
print(f"⏱️  Executed at: {executed_at.strftime('%Y-%m-%d %H:%M:%S')}")
print(f"   Python {platform.python_version()} on {platform.system()} ({platform.machine()})")

⏱️  Executed at: 2026-05-06 13:26:41
   Python 3.13.12 on Darwin (arm64)

The timestamp above is frozen. On a normal build, this cell is skipped — Quarto loads the cached output from _freeze/ instead of running the code.

A “Slow” Computation

To make the demo more convincing, here’s a computation that simulates expensive work:

# Simulate an expensive operation (e.g., MCMC sampling, model training)
print("Running expensive computation...")
start = time.time()

# Compute SHA-256 hashes in a loop (simulates ~2 seconds of work)
result = b"great-docs-freeze-demo"
for i in range(500_000):
    result = hashlib.sha256(result).digest()

elapsed = time.time() - start
final_hash = hashlib.sha256(result).hexdigest()[:16]

print(f"✓ Completed in {elapsed:.2f}s")
print(f"  Result hash: {final_hash}")
print(f"  Iterations: 500,000")

Running expensive computation...
✓ Completed in 0.15s
  Result hash: 6ecf43c8b72d40b6
  Iterations: 500,000

Without freeze, this cell would add ~2 seconds to every build. With freeze enabled, the cached output is reused instantly.

How This Page Is Configured

This page uses the simplified frontmatter syntax:

---
title: "Freeze a Page to Cache Outputs"
freeze: auto
---

During the build, Great Docs normalizes this to:

---
execute:
  freeze: auto
---

The great-docs.yml for this site has freeze: auto set — Great Docs automatically handles restoring _freeze/ into the build directory before Quarto renders. No extra scripts or configuration needed.

Reproducing This

To update this page’s cached outputs (for example, after changing the code above):

Terminal

great-docs freeze recipes/24-freeze-demo.qmd
git add _freeze/
git commit -m "Refresh freeze demo outputs"

This re-executes the cells, captures the new outputs in _freeze/, and the updated timestamp proves the refresh happened.