48 lines
2.1 KiB
Plaintext
48 lines
2.1 KiB
Plaintext
Behind the scenes
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=================
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This document assumes you already have an up and running instance of
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Django Compressor, and that you understand how to use it in your templates.
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The goal is to explain what the main template tag, {% compress %}, does
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behind the scenes, to help you debug performance problems for instance.
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First step: Offline cache
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-------------------------
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The first thing {% compress %} tries to do is get the offline cache for its
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nodelist if offline cache is activated. It doesn't parse, doesn't check the
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modified times of the files, doesn't even know which files are concerned
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actually, since it doesn't look inside the nodelist of the template block
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enclosed by the ``compress`` template tag. The cache should return the HTML
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containing the element code for the combined file or piece of code (which,
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if the cache key exists, is supposed to already exist on disk/custom storage).
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Everything stops here if the cache entry exists.
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Second step: parsing and file list
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----------------------------------
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A compressor instance is created, which in turns instantiates the HTML parser.
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The parser is used to determine a file or code hunk list. Each file mtime is
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checked, first in cache and then on disk/storage, and this is used to
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determine an unique cache key.
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Third step: Checking the "main" cache
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-------------------------------------
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Compressor checks if it can get some info about the combined file/hunks
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corresponding to its instance, using the cache key obtained in the previous
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step. The cache content here will actually be the HTML containing the final
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element code, just like in the offline step before.
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Everything stops here if the cache entry exists.
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Fourth step: Generating the combined file if needed
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---------------------------------------------------
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The file is generated if necessary. All precompilers are called and all
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filters are executed, and a hash is determined from the contents. This in
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turns helps determine the file name, which is only saved if it didn't exist
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already. Then the HTML output is returned (and also saved in the cache).
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And that's it!
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