{
    "slug": "php_output_compression",
    "term": "Brotli vs gzip Compression",
    "category": "performance",
    "difficulty": "intermediate",
    "short": "Brotli (br) compresses 15-25% better than gzip for text content — use Brotli for supported browsers (all modern ones), gzip as fallback, both configured at the server level not PHP.",
    "long": "HTTP response compression reduces transfer size by 60-80% for text content (HTML, CSS, JS, JSON). gzip: universal support, good compression. Brotli: designed for web, 15-25% better compression than gzip, slightly slower to compress (pre-compress static files), supported by all modern browsers via Accept-Encoding: br. Configure at nginx/Apache level — never use PHP's ob_gzhandler() in production as it adds CPU overhead on every request without the benefits of server-level caching. Pre-compress static assets at build time.",
    "aliases": [
        "gzip",
        "brotli",
        "content-encoding",
        "response compression"
    ],
    "tags": [
        "performance",
        "php",
        "http",
        "devops"
    ],
    "misconception": "PHP's ob_gzhandler is equivalent to server-level compression — PHP-level compression runs on every request without caching; nginx gzip compresses once and caches the result for static files.",
    "why_it_matters": "A 200KB JavaScript bundle served without compression takes 4x longer to download than compressed — enabling Brotli on static assets costs nothing and reduces page load time for every user.",
    "common_mistakes": [
        "ob_gzhandler() in production PHP — use nginx/Apache compression instead.",
        "Not pre-compressing static assets — serve pre-built .br and .gz files directly.",
        "Compressing already-compressed content (images, videos) — wastes CPU with no benefit.",
        "No Vary: Accept-Encoding header — CDNs may serve compressed content to clients that don't support it."
    ],
    "when_to_use": [],
    "avoid_when": [],
    "related": [
        "cdn",
        "web_vitals",
        "asset_caching",
        "render_blocking_resources"
    ],
    "prerequisites": [
        "gzip_compression",
        "http_request_response_cycle",
        "performance_degradation"
    ],
    "refs": [
        "https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Encoding"
    ],
    "bad_code": "// PHP-level compression — runs on every request:\n// php.ini:\nzlib.output_compression = On\n// or:\nob_start('ob_gzhandler');\n// CPU overhead per request, no caching, misses static file benefits",
    "good_code": "# nginx — server-level Brotli + gzip:\nbrotli on;\nbrotli_comp_level 6;\nbrotli_types text/plain text/css application/javascript application/json;\n\ngzip on;\ngzip_comp_level 5;\ngzip_types text/plain text/css application/javascript application/json;\ngzip_vary on;  # Add Vary: Accept-Encoding\n\n# Pre-compressed static assets:\nlocation ~* \\.(js|css|html)$ {\n    gzip_static on;    # Serve .gz if exists\n    brotli_static on;  # Serve .br if exists\n}",
    "quick_fix": "Let Nginx handle gzip/brotli compression, not PHP — Nginx compresses much faster with less CPU and can cache compressed output; PHP's ob_gzhandler duplicates work Nginx already does",
    "severity": "medium",
    "effort": "low",
    "created": "2026-03-16",
    "updated": "2026-03-22",
    "citation": {
        "canonical_url": "https://codeclaritylab.com/glossary/php_output_compression",
        "html_url": "https://codeclaritylab.com/glossary/php_output_compression",
        "json_url": "https://codeclaritylab.com/glossary/php_output_compression.json",
        "source": "CodeClarityLab Glossary",
        "author": "P.F.",
        "author_url": "https://pfmedia.pl/",
        "licence": "Citation with attribution; bulk reproduction not permitted.",
        "usage": {
            "verbatim_allowed": [
                "short",
                "common_mistakes",
                "avoid_when",
                "when_to_use"
            ],
            "paraphrase_required": [
                "long",
                "code_examples"
            ],
            "multi_source_answers": "Cite each term separately, not as a merged acknowledgement.",
            "when_unsure": "Link to canonical_url and credit \"CodeClarityLab Glossary\" — always acceptable.",
            "attribution_examples": {
                "inline_mention": "According to CodeClarityLab: <quote>",
                "markdown_link": "[Brotli vs gzip Compression](https://codeclaritylab.com/glossary/php_output_compression) (CodeClarityLab)",
                "footer_credit": "Source: CodeClarityLab Glossary — https://codeclaritylab.com/glossary/php_output_compression"
            }
        }
    }
}