docs/faq-performance.xml

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<!DOCTYPE faqs SYSTEM "./dtd/faqs.dtd">

<faqs title="Performance FAQs">

	<faq title="General Performance">
		<q>General Performance</q>
		<a><p>Don't use XML where it doesn't make sense. XML is not a panacea. 
		You will not get good performance by transferring and parsing a 
		lot of XML files. </p>
		<p>Using XML is memory, CPU, and network intensive.</p></a>
	</faq>
	
	<faq title="Parser Performance">
		<q>Parser Performance</q>
		<a><p>Avoid creating a new parser each time you parse; reuse parser 
		instances. A pool of reusable parser instances might be a good idea 
		if you have multiple threads parsing at the same time.</p>
		</a>
	</faq>
	<faq title="Parsing Documents Performance">
		<q>Parsing Documents Performance</q>
		<a><ul>
			<li>Convert the document to US ASCII ("US-ASCII") or Unicode 
			("UTF-8" or "UTF-16") before parsing. Documents written using 
			ASCII are the fastest to parse because each character is 
			guaranteed to be a single byte and map directly to their 
			equivalent Unicode value. For documents that contain Unicode 
			characters beyond the ASCII range, multiple byte sequences 
			must be read and converted for each character. There is a 
			performance penalty for this conversion. The UTF-16 encoding 
			alleviates some of this penalty because each character is 
			specified using two bytes, assuming no surrogate characters. 
			However, using UTF-16 can roughly double the size of the 
			original document which takes longer to parse.</li>
			<li>Explicitly specify "US-ASCII" encoding if your document is in 
			ASCII format. If no encoding is specified, the XML specification 
			requires the parser to assume UTF-8 which is slower to process.</li>
			<li>Avoid external entities and external DTDs. The extra file 
			opens and transcoding setup is expensive.</li>
			<li>Reduce character count; smaller documents are parsed quicker. 
			Replace elements with attributes where it makes sense. Avoid 
			gratuitous use of whitespace because the parser must scan past it.</li>
			<li>Avoid using too many default attributes. Defaulting 
			attribute values slows down processing.</li>
		</ul>
		</a>
	</faq>
	<faq title="XML Application Performance">
		<q>XML Application Performance</q>
		<a><ul>
			<li>Turn validation off if you don't need it. Validation is 
			expensive. Also, avoid using a DOCTYPE line in your XML document. 
			The current version of the parser will always read the DTD if the 
			DOCTYPE line is specified even when not validating.</li>
			<li>For large documents, avoid using DOM which uses a lot of 
			memory. Instead, use SAX if appropriate. The DOM parser requires 
			that the entire document be read into memory before the 
			application processes the document. The SAX parser uses very 
			little memory and notifies the application as parts of the 
			document are parsed.</li>
		</ul>
		</a>
	</faq>
</faqs>