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Update the FormulaEvaluator performance section to match current behaviour 

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1348657 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Nick Burch 2012-06-10 20:40:32 +00:00
parent a69bdc08ba
commit e06949f47d
1 changed files with 37 additions and 24 deletions
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61
src/documentation/content/xdocs/spreadsheet/eval.xml
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@ -272,28 +272,41 @@ for(int sheetNum = 0; sheetNum < wb.getNumberOfSheets(); sheetNum++) {
</source> </source>
</section> </section>
<anchor id="Performance"/> <anchor id="Performance"/>
<section><title>Performance Notes</title> <section><title>Performance Notes</title>
<ul> <ul>
<li>Generally you should have to create only one FormulaEvaluator <li>Generally you should have to create only one FormulaEvaluator
instance per sheet, but there really is no overhead in creating instance per Workbook. The FormulaEvaluator will cache
multiple FormulaEvaluators per sheet other than that of the evaluations of dependent cells, so if you have multiple
FormulaEvaluator object creation. formulas all depending on a cell then subsequent evaluations
</li> will be faster.
<li>Also note that FormulaEvaluator maintains a reference to </li>
the sheet and workbook, so ensure that the evaluator instance <li>You should normally perform all of your updates to cells,
is available for garbage collection when you are done with it before triggering the evaluation, rather than doing one
(in other words don't maintain long lived reference to cell at a time. By waiting until all the updates/sets are
FormulaEvaluator if you don't really need to - unless performed, you'll be able to take best advantage of the caching
all references to the sheet and workbook are removed, these for complex formulas.
don't get garbage collected and continue to occupy potentially </li>
large amounts of memory). <li>If you do end up making changes to cells part way through
</li> evaluation, you should call <em>notifySetFormula</em> or
<li>CellValue instances however do not maintain reference to the <em>notifyUpdateCell</em> to trigger suitable cache clearance.
Cell or the sheet or workbook, so these can be long-lived Alternately, you could instantiate a new FormulaEvaluator,
objects without any adverse effect on performance. which will start with empty caches.
</li> </li>
</ul> <li>Also note that FormulaEvaluator maintains a reference to
</section> the sheet and workbook, so ensure that the evaluator instance
</body> is available for garbage collection when you are done with it
(in other words don't maintain long lived reference to
FormulaEvaluator if you don't really need to - unless
all references to the sheet and workbook are removed, these
don't get garbage collected and continue to occupy potentially
large amounts of memory).
</li>
<li>CellValue instances however do not maintain reference to the
Cell or the sheet or workbook, so these can be long-lived
objects without any adverse effect on performance.
</li>
</ul>
</section>
</body>
</document> </document>