O(n^2) operation in xmlbeans would like to make O(n log n) or better
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Key: XMLBEANS-438
URL: https://issues.apache.org/jira/browse/XMLBEANS-438
Project: XMLBeans
Issue Type: Improvement
Affects Versions: Version 2.4
Environment: Using XMLbeans inside of POI when saving spreadsheets in
the XLSX file format.
Reporter: Bryce Alcock
Using POI to save a spread sheet in XLSX format causes an O(n^2) operation to
occur.
Specifically:
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 pf
XmlComplexContentImpl.java method arraySetterHelper)
-----------------------------------------------------------
// 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;
}
I will add a sample code showing exactly how to reproduce this issue.
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