Max fetch size in DataScrollerComponent

Question

Hi
If i cap a max fetch size of 2000 on a query that i know will return 8000 rows the DataScroller still reports 1-rageSize of 8000 ?
If i try and navigate past row 2000 the component correctly sees the max fetch size and displays 1-rangeSize of 2000 ??
Whats going on ?
Thanks
Matt

Answer 1

Got to the bottom of this by replacing a the code in the DataScroller component so we could view (and change) the source code. The component files are :
ScrollBarTag.java - used in <jbo:DataScroller> tag
DataScrollerComponent.jsp - the page that renders the dropdown list and next / previous values
DataScroller.java - the bean used in the jsp that contains state information about the current datasource.
When the DataScroller bean is initialised it sets up range values to enable calculation of entries in the scroller (e.g 1-100 0f 1000000). It derives the datasource from PageContext and looks at the RowSet directly.
The problem is that it uses the getEstimatedRowCount() API on the RowSet driectly (i.e. not via the ViewObject).
This figure returned doesnt consistently obey a cap on the max fetch size and will be a nasty bottleneck if you are querying on very large result sets. Mysteriously, if you try to navigate past the end of your maxFetchSize in the scroller the second pass through the code will get the estimated row count correct and obey the cap on maxFetchSize ?
If you change the call to use the getRowCount() API instead, this figure seems to consistently obey the maxFetchSize cap.
We had to look into this code as this component will perform very badly against 6 and 7 figure ResultSets as its not taking into account any caps set.
As a matter of interest, changing the code in the bean to ask the view object directly for its getEstimatedRowCount() seems to consistently obey any caps !?! :
ds = Utils.getDataSourceFromContext(pageContext, dsName);
RowSet rs = ds.getRowSet();
ApplicationModule am = rs.getApplicationModule();
ViewObject dvo = am.findViewObject(Constants.SOME_DVO);
if (dvo != null)
System.out.println("dvo "+dvo.getName());
System.out.println("est rows "+dvo.getEstimatedRowCount());
System.out.println("rows "+dvo.getRowCount());
This code will get the figure right and if run before the
rs.getEstimatedRowCount seems to force the correct value in the RowSet.
Matt