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Re: Re: [jdom-interest] Re: Reading XML with JDOM

David Wall

2008-10-03

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Michael has it right -- penny-wise and pound foolish won't result in a good performing system.

If your XML is really that simple, maybe XML parsing it is not even the right solution, though SAX would surely do well.  Much depends on how much data transformation is needed.  Your firstname, lastname and SSN fields likely don't have to be encoded elements, so a simple string parsing may do much better, such as searching for "<lastname>" and the pulling the data until you find "</".

XML parsers are very general, so they are very useful.  But if your data is simple, you may find simple string parsing yourself to be the fastest.

David



Michael Kay wrote:
The point of my message is that if it's taking 1 second to get the file over the network and 1msec to process the file, then improving the processing speed to 0.9 msec is a waste of effort. It's like tuning your car's engine and leaving the handbrake on. You need to understand the overall system performance (and the extent to which it falls short of the performance requirements) before you decide which parts of it to tune.
 
Michael Kay
http://www.saxonica.com/


From: Praveen Gattu [mailto:pgattu@gmail.com]
Sent: 03 October 2008 01:32
To: Michael Kay
Cc: Paul Libbrecht; jdom-interest@jdom.org
Subject: Re: [jdom-interest] Re: Reading XML with JDOM

Michael

The XML is to be obtained over a www URL. Our networks are T1 speed and performing their best. There isn't a problem with the network latency, but I acknowledge that retrieving the XML file over a www URL is probably the most time consuming procedure for my application. Www Network latency aside, I want to assure that whatever APIs/frameworks I use for parsing the XML are the fastest. For the purposes of measuring the performance of the parser, I am using a XML file located in the file system and removing the network latency aspect. Is this a valid method to measure the parser's performance?

-- Praveen

On Thu, Oct 2, 2008 at 3:49 PM, Michael Kay <mike@saxonica.com> wrote:
You're asking about how to read the data efficiently with JDOM, but I suspect that if you are looking for performance then you might be looking in the wrong part of your system.
 
XML parser start-up costs can be very high; initializing the parser for each document could easily turn out to be the dominant cost in this application. You can get a lot of saving by reusing parser instances. I don't know what JDOM's initialization costs for building a document are, but you need to check them too.
 
At any rate, building a JDOM tree almost certainly takes longer than extracting the data from the tree once built.
 
I find this statement a bit worrying:
 
>Anyway, since there is probably not much I can do with the network latency, I am trying to keep the Java code as skinny and efficient as possible.
That seems to be an inversion of the way performance engineering should be done. If network latency is the dominant cost, then effort spent on tuning your Java code is a total waste of time.
 
I would focus your attention on measuring performance, end to end, before you start tuning anything.
 
Michael Kay


From: jdom-interest-bounces@jdom.org [mailto:jdom-interest-bounces@jdom.org] On Behalf Of Praveen Gattu
Sent: 02 October 2008 23:04
To: Paul Libbrecht
Cc: jdom-interest@jdom.org
Subject: Re: [jdom-interest] Re: Reading XML with JDOM

Paul,

Thanks for the response. My XML is really as simple as the one I posted. The 8,500 documents are retrieved over a HTTP URL. So add network latency, which makes it longer than a minute, unless my XML parser is extremely fast. Anyway, since there is probably not much I can do with the network latency, I am trying to keep the Java code as skinny and efficient as possible.

Would you be able to provide sample code for the solution you suggested?

On Thu, Oct 2, 2008 at 2:27 PM, Paul Libbrecht <paul@activemath.org> wrote:
Praveen,

in jdom you would just parse then take the root, then the employee, the extract last-name and ssn.
It is ignoring from the point of view of your programme but not from the point of view of parsing.

Where you can save is by changing the xml technology... if your document is as simple as below then using sax has greater performance guarantees (you really cannot go faster) but is harder to programme with.
Another part where jdom can take too much of your CPU is if this document has loads of other stuffs.

Where JDOM would make a positive difference is at walking more elaborate xml documents, which is the norm, and at manipulating them. The expressivity of the library there is unbeatable to my taste.

However, your requirements sound easy: 8500 such documents per minutes?
JDOM does this probably ten times, multithreadedness not being really necessary.

paul


On 02-oct.-08, at 20:29, Praveen Gattu wrote:

I have a XML as below. There is always "only one" employee node in the XML. So rather than iterating through the nodes, I want to read the lastname and ssn directly, while ignoring the firstname. What is the best way to do this in JDOM? My most important criteria is speed. We will be processing about a 8,500 of such XML documents per minute  (multi-threaded of course) and need something efficient and fast. I appreciate any help you can offer in this regard.

<response>
 <employee>
   <firstname>John</firstname>
   <lastname>Smith</lastname>
   <ssn>111-11-1111</ssn>
 </employee>
</response>

--
Thanks,
Praveen




--
Thanks,
Praveen
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David A. E. Wall
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