Style sheet processing optimization
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Key: ADFFACES-394
URL: https://issues.apache.org/jira/browse/ADFFACES-394
Project: MyFaces ADF-Faces
Issue Type: Improvement
Components: Skinning
Affects Versions: 2.0.0-incubating-core-SNAPSHOT,
1.0.0-incubating-core-SNAPSHOT
Environment: Windows XP
Reporter: Andy Schwartz
Priority: Minor
While investigating performance of initial page delivery I noticed that on the
very first page delivery a large percentage of the time is spent in style sheet
processing code. In particular, a bit of profiling reveals that
StyleSheetDocument.getStyles() - specifically the calls to _resolveStyle() -
can be expensive. On a slower machine with a large custom stylesheet this can
add up to several seconds. Interestingly, this particular performance problem
is self-documenting... The following comment taken from
StyleSheetDocument.java:
// Now, loop through all StyleNodes in all StyleSheetNodes
// Note: The algorithm used here is actually much more inefficient
// than it needs to be. We're using a n-squared algorithm here -
// for every style we find, we need to loop through all other styles.
// The reason for this is because this allows us to share code
// (namely _resolveStyle()) with getStyleBySelector/Name(). However,
// we could probably double the performance of CSS generation by
// optimizing this routine to make a single pass through all styles,
// and then resolve everything in one step.
Leaving aside questions about whether "doubling" the performance would be the
actual result :-) , the idea is that this would work as follows:
- First pass built up a mappings from selector/name to a list of matching
StyleNodes.
- The second pass then resolves the styles based on the mappings created in the
first pass.
This should avoid the current n-squared behavior and presumably reduce the
amount of time spent in this code, thus speeding up initial page delivery.
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