diff --git a/docs/topics/performance.txt b/docs/topics/performance.txt index 2265e52462..d015558b32 100644 --- a/docs/topics/performance.txt +++ b/docs/topics/performance.txt @@ -150,8 +150,8 @@ so there can be huge benefit in saving the value to a quickly accessible cache, ready for the next time it's required. It's a sufficiently significant and powerful technique that Django includes a -comprehensive caching framework, as well as numerous other opportunities to -make use of caching. +comprehensive caching framework, as well as other smaller pieces of caching +functionality. :doc:`The caching framework ` -------------------------------------------- @@ -168,14 +168,8 @@ Implementing caching should not be regarded as an alternative to improving code that's performing poorly because it has been written badly. It's one of the final steps towards producing well-performing code, not a shortcut. -Other opportunities for caching -------------------------------- - -Beyond the caching framework, Django offers other smaller pieces of caching -functionality. - :class:`~django.utils.functional.cached_property` -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +------------------------------------------------- It's common to have to call a class instances's method more than once. If that function is expensive, then doing so can be wasteful. @@ -186,14 +180,8 @@ the saved value rather than re-computing it. Note that this only works on methods that take ``self`` as their only argument and that it changes the method to a property. -:class:`~django.contrib.staticfiles.storage.CachedStaticFilesStorage` -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -:class:`~django.contrib.staticfiles.storage.CachedStaticFilesStorage` appends a -content-dependent tag to the filenames of :doc:`static files -` to make it safe for browsers to cache them -long-term without missing future changes - when a file changes, so will the -tag, so browsers will reload the asset automatically. +Certain Django components also have their own caching functionality; these are +discussed below in the sections related to those components. Understanding laziness ====================== @@ -284,11 +272,31 @@ time. Note that GZipMiddleware is currently considered a security risk, and is vulnerable to attacks that nullify the protection provided by TLS/SSL. See the warning in :class:`~django.middleware.gzip.GZipMiddleware` for more information. -Third-party HTTP tools ----------------------- +Static files +------------ -There are numerous third-party Django tools and packages available, notably -ones that are able to "minify" and compress HTML, CSS and JavaScript. +Static files, which by defintion are not dynamic, make an excellent target for +optimization gains. + +:class:`~django.contrib.staticfiles.storage.CachedStaticFilesStorage` +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +By taking advantage of web browsers' caching abilities, you can +eliminate network hits entirely for a given file after the initial download. + +:class:`~django.contrib.staticfiles.storage.CachedStaticFilesStorage` appends a +content-dependent tag to the filenames of :doc:`static files +` to make it safe for browsers to cache them +long-term without missing future changes - when a file changes, so will the +tag, so browsers will reload the asset automatically. + +"Minification" +^^^^^^^^^^^^^^ + +Several third-party Django tools and packages provide the ability to "minify" +HTML, CSS, and JavaScript. They remove uneccessary whitespace, newlines, and +comments, and shorten variable names, and thus reduce the size of the documents +that your site publishes. Template performance ==================== @@ -313,13 +321,19 @@ Using different versions of available software It can sometimes be worth checking whether different and better-performing versions of the software that you're using are available. -This may be helpful, but is unlikely to solve a serious performance problem. -You won't usually gain performance advantages that are better than marginal. +These techniques are targeted at more advanced users who want to push the +boundaries of performance of an already well-optimized Django site. + +However, they are not magic solutions to performance problems, and they're +unlikely to bring better than marginal gains to sites that don't already do the +more basic things the right way. .. note:: It's worth repeating: **reaching for alternatives to software you're - already using is very rarely the answer to performance problems**. + already using is never the first answer to performance problems**. When + you reach this level of optimization, you need a formal benchmarking + solution. Newer is often - but not always - better ---------------------------------------- @@ -369,16 +383,36 @@ templating language. Alternative software implementations ------------------------------------ -It *may* be worth checking whether Python software you're using has been +It may be worth checking whether Python software you're using has been provided in a different implementation that can execute the same code faster. -However, most Django performance problems in well-written code are typically -not to be found at the Python execution level, but rather in inefficient -database querying, caching, and templates (and if you're relying on -poorly-written Python code, your performance problems are very unlikely to be -solved by having it execute faster). +However: most performance problems in well-written Django sites aren't at the +Python execution level, but rather in inefficient database querying, caching, +and templates. If you're relying on poorly-written Python code, your +performance problems are unlikely to be solved by having it execute faster. -Avoid using C implementations of Python libraries or non-standard Python -implementations like `PyPy `_ in search of performance gains, -unless you are sure they are appropriate for your application. Any gains are -likely to be small, and compatibility issues are common. +Using an alternative implementation may introduce compatibility, deployment, +portability, or maintenance issues. It goes without saying that before adopting +a non-standard implementation you should ensure it provides sufficient +performance gains for your application to outweigh the potential risks. + +With these caveats in mind, you should be aware of: + +`PyPy `_ +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +`PyPy `_ is an implementation of Python in Python itself (the +'standard' Python implementation is in C). PyPy can offer substantial +performance gains, typically for heavyweight applications. + +A key aim of the PyPy project is `compatibility +`_ with existing Python APIs and libraries. +Django is compatible, but you will need to check the compatibility of other +libraries you rely on. + +C implementations of Python libraries +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Some Python libraries are also implemented in C, and can be much faster. They +aim to offer the same APIs. Note that compatibility issues and behaviour +differences are not unknown (and not always immediately evident).