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https://issues.apache.org/jira/browse/XMLBEANS-389?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12664059#action_12664059
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Philip Aston commented on XMLBEANS-389:
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Of course. I guess I was really expecting the list accessors to take a snapshot
like the array accessor.
Here's a jump start for the doc:
When a schema is compiled with -javasource=1.5, java.util.List based
accessors are generated as well as the array accessors. Unlike the
array accessors, the returned lists are live. Changes to a List are
reflected in the underlying XMLBean, and changes to the XMLBean are
reflected in the List.
This live behavior makes iteration over large lists inefficient. Each
time an Iterator.hasNext() or Iterator.next() is called, the iterator
walks over the underlying XMLBean structure. This scales poorly with
as the size of the list grows, so the list accessors should only be
used for small sequences.
To create a non-live list efficiently, avoid the list accessors.
Instead construct a new java.util.ArrayList around an array returned
from an array accessor.
> List accessors generated with -javasource=1.5 produce lists that scale poorly
> with the size of the list
> -------------------------------------------------------------------------------------------------------
>
> Key: XMLBEANS-389
> URL: https://issues.apache.org/jira/browse/XMLBEANS-389
> Project: XMLBeans
> Issue Type: Bug
> Components: Compiler
> Affects Versions: Version 2, Version 2.1, Version 2.2, Version 2.2.1,
> Version 2.3, Version 2.3.1, Version 2.4 , Version 2.4.1
> Reporter: Philip Aston
> Attachments: testcase.tgz
>
>
> When a schema is compiled with -javasource=1.5, convenient list based
> accessors are generated as well as the array accessors. E.g.
> java.util.List<java.lang.String> getParamList()
> The implementation of the List is built upon java.lang.AbstractList. The
> AbstractList iterator's hasNext() method calls size(). For an XMLBean
> generated list, size() walks the store and so iteration scales quadratically.
> Here are some numbers showing the problem:
> XMLBeans backed list of 1 strings: 0.013766 ms
> XMLBeans backed list of 16 strings: 0.255458 ms
> XMLBeans backed list of 256 strings: 1.612057 ms
> XMLBeans backed list of 1024 strings: 25.458934 ms
> XMLBeans backed list of 2048 strings: 123.393447 ms
> XMLBeans backed list of 4096 strings: 505.594661 ms
> plain list of 1 strings: 0.002304 ms
> plain list of 16 strings: 0.007788 ms
> plain list of 256 strings: 0.013384 ms
> plain list of 1024 strings: 0.052215 ms
> plain list of 2048 strings: 0.103550 ms
> plain list of 4096 strings: 0.206648 ms
> I think the generated list should override iterator(), and return an Iterator
> that calculates the list size once per iteration.
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