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Subject [WIKI-UPDATE] Main WritingPipelineComponents WritingForCacheEfficiency Wed May 14 12:00:05 2003
Date Wed, 14 May 2003 10:00:05 GMT
Page: , version: 185 on Wed May 14 09:33:30 2003
by SylvainWallez

- * May 13, 2003
?        ^

+ * May 14, 2003
?        ^

Page: , version: 3 on Wed
May 14 09:18:24 2003 by SylvainWallez

+ * __[Writing components for maximum cache efficiency|WritingForCacheEfficiency]__

Page: , version: 1 on Wed
May 14 09:27:57 2003 by SylvainWallez

New page created:
+ Pipeline components can be made cacheable by implementing {{CacheableProcessingComponent}}.
This allows the component to give a cache key and validity used to avoid useless reprocessing
if the pipeline result would be unchanged.
+ However, achieving maximum performance to deliver cached content needs some careful coding.
+ Looking at {{TraxTransformer.setup()}} (as of 13 may 2003), we can see that it gets the
validity _and_ and a TransformerHandler at the same time. And if the validity is still valid,
the TransformerHandler is simply not used since the content is retrieved from the cache. So
I hacked a bit to separate these, and obtained again a speed increase ranging from 5% to 30%.
+ This leads to some importants recommendations in order to achieve the maximum cache efficiency
: __the {{setup()}} method must avoid performing operations that are necessary only if the
content is not cached__. Otherwise, its just a waste of speed to deliver cached content.
+ Here's a reminder of the various steps that occur when handling a request :\\
+ __1__ - the sitemap is executed, meaning we create a pipeline object, and pipeline components
: generator, transformers, and serializer.\\
+ __2__ - the {{setup()}} method of all pipeline components is called (except serializer which
doesn't have one)\\
+ __3__ - the {{getKey()}} method of all pipeline components is called
+ Knowing the key, the pipeline can get the associated cache entry and its validity. If the
cache validity either is invalid or needs a fresh validity object to be compared with, then
+ __4__ - the {{getValidity()}} method of all pipeline components is called
+ The pipeline can then know if the cache entry is valid. If it's valid, it delivers the cached
content. If it's invalid, then :\\
+ __5__ - the pipeline is connected. This means {{setXMLConsumer()}} is called on transformers
and {{setOutputStream()}} is called on the serializer\\
+ __6__ - the generator's {{generate()}} method is called, and starts the SAX stream processing,
resulting first in {{startDocument()}} being called on transformers and serializer.
+ What we can see above, is that we must defer as much as possible to points 5 or 6 the creation
or lookup of resources that are used to process the content. Doing it before is only waste
of resources. And that's what TraxTransformer is doing : it creates a TransformerHandler at
point 2.
+ Be aware of that and inspect cacheable components for possible enhancements. This is key
for an increased performance !
+ -- [SylvainWallez]

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