POI uses XMLBeans,
This is a problem to help make POI faster:
There has been on going discussion in the dev.at.poi.apache.org list,
However I will include back ground here.
This issue is significant.
Took your suggestion and pulled XMLBeans 2.4 into POI,
it worked but contained the O(n^2) issue.
I have spent some time further investigating this, and it is
fairly simple to analyse and understand why it is O(n^2).
The real question is what can we do.
NOTE: My line numbers won't match with SVN because I have modified the code to
put
some timers and system outs in place.
Just a Quick overview
it seems like XmlComplexContentImpl.arraySetterHelper iterates over all
elements in the spread sheet.
then in side of that iteration, the Xobj.find_element_user(Qname,int) is an
Order n operation.
Just making Xobj.find_element_user a O(log n) would completely solve the
problem.
ANALYSIS: O(n^2) in XML Beans: (Around Line 1153 or so....)
-----------------------------------------------------------
// Order N (this is invoked 1 time for each element in sources (~120,000
records in my case)
for ( i++, j++; i < sources.length; i++, j++)
{
long t1 = System.currentTimeMillis();
XmlCursor c = sources[i].isImmutable() ? null : sources[i].newCursor();
getCursorTime += (System.currentTimeMillis()-t1);
long t2=System.currentTimeMillis();
if (c != null && c.toParent() && c.getObject() == this)
{
ifCheckTime += (System.currentTimeMillis()-t2);
long t3 = System.currentTimeMillis();
c.dispose();
long t4 = System.currentTimeMillis();
// THIS CAUSES O(n^2) SEE CODE BELOW, but this on O(n) for each record.
// THIS IS THE INEFFICIENCY in XMLBeans...
current = store.find_element_user( elemName, j );
findUserElement += (System.currentTimeMillis() - t4);
if (current == sources[i])
; // advance
else
{
// Fall back to the general case
break;
}
insideIfTime += (System.currentTimeMillis()-t3);
}
else
{
ifCheckTime += (System.currentTimeMillis()-t2);
c.dispose();
// Insert before the current element
TypeStoreUser user = store.insert_element_user( elemName, j );
((XmlObjectBase) user).set( sources[i] );
}
}
---------------- Method from store.find_element_user(QName,int i)---------
// THIS METHOD IS 0(n)
// but this is called n times by XmlComplexContentImpl.java around line
1153....
public TypeStoreUser find_element_user ( QName name, int i )
{
for ( Xobj x = _firstChild ; x != null ; x = x._nextSibling )
if (x.isElem() && x._name.equals( name ) && --i < 0)
return x.getUser();
return null;
}
Best regards
Bryce
------------------------------------------------------------------------------------------
Bryce Alcock * Performance Architect * SunGard *
Asset Arena * 377 E. Butterfield Road Suite 800, Lombard, IL 60148 *
Tel 630-986-3006 *
www.sungard.com/assetarena
..........................................................................................
http://www.brycealcock.com/
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