Don't call IDataProvider.size method when IDataProvider.iterator(first, count)
returned the number of elements less than "count"
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Key: WICKET-2618
URL: https://issues.apache.org/jira/browse/WICKET-2618
Project: Wicket
Issue Type: Improvement
Components: wicket
Affects Versions: 1.4.4
Reporter: Michael Mikhulya
IDataProvider has two mehtods:
Iterator<? extends T> iterator(int first, int count);
int size()
which in many implementations do access to database.
Normally iterator do SQL query with LIMIT and OFFSET, and size do SQL COUNT
query.
SQL COUNT is O(N) for most transactional databases (e.g. for postgresql) and so
it is rather heavy.
In some cases it is possible to avoid call to IDataProvider.size method.
For example when "iterator" returned the number of elements less than acquired
"count".
This case appears in 90% in my application (whenever search is used normally
number of found elements is less than number of elements on page).
Also pgFouine shows me these queries as the most slow one. So I suggest to
implement this optimization.
First I though that appropriate place to implement it is AbstractPageableView
class, but unfortunatelly not all IPageable classes extends this abstract class
(for example DataTable doesn't do so).
So I suggest to implement Decorator of IDataProvider and reuse it in
DataViewBase, DataTable, ...
If nobody see any problems with this suggestion I would like to implement it on
my own.
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